Introduction |
Mechanics |
Steam engine | To the top |
We are Bogdan and Ionel .We are 13 years old. We are studying at “Nicolae Titulescu ” High school.
We needed the next materials:
• a sardine can
• a piece of wood
• a thin pipe
• 20 centimeters of wire
• a propeller
• sanitary alcohol
Way of work
In the sardine can we made a hole to get out the inside. We couldn’t so we cut the fish with a screw. After that we put the thin pipe in the hole .
On the wood piece we make a support for the can . Under the can I put a little plate with alcohol . We put the propeller in front of the pipe from the can .
We put on fire the plate with alcohol , and under the can .
After 5 or 10 minutes the steam will come out the propeller will spin.
THAT’S THE STEAM ENGINE!
With this experimental device we won a first price to the first edition of Science Fair contest organized by Comenius 3 "Hands on Science" network in Bucharest.
How it works?
When water is heated, it reaches 100 degrees Celsius and then stays at that temperature as the water changes into steam. As the temperature rises, the molecules move faster and faster and beat against the propeller until they force it to move. The heat energy of the steam is converted in kinetic energy of the propeller.
Automatic signal | To the top |
Our Physics teacher, Mrs. Elena Vladescu, told us about steps of a scientific experiment. I thought to try an application to the lesson “Expansion”.
1. Initial remarks and our questions about the phenomenon
We observed that if we heat two different metals, they have different extensions. Why?
This fact happened because some metals warm quickly than others.
2. The aim of the experiment
We put in evidence the behavior of a bimetallic lamella in a practical application.
3. The choice of the project’s title
I choose this name because that is very suggestive.
4. Materials used: a 4,5 V battery, electrical conductors, a bulb, a wood piece, two lamellas (one of copper and other of sheet iron) and a support.
5. The hypothesis.
I think that, if I heat the metallic lamellas, the copper lamella will bend and touch the console and the bulb light.
6. How I built my experiment?
My father helped me to make this device and then I verified the hypothesis for several times to see if I obtain the same results. This is true. I warmed lamellas with a briquette, lamellas expand different, because were made from different materials and will have a curve form. In this way, the circuit is closed and the bulb light.
7. Conclusions
I verified the hypothesis and I think that it have many practical applications. I like Physics.
8. How it works?
When objects get hotter they grow bigger. We say that expand.
When objects cool down they get smaller. We say they contract.
A bi-metallic strip is made of two different metal strips fixed together (copper and iron) which are placed side by side and them holded together very tightly (riveted or welded).
When heated, copper expands more than iron and so the strip bends with copper on the outside because it is longer.
Applications: a fire-alarm, an electric thermostat, gas thermostat for a gas oven.
Liquids expand more than solids and gases expand more than liquids.
Substances expand because the molecules are moving more and take up more space.
Vehicle with rubber engine | To the top |
Hi! I am Victor from „Nicolae Titulescu” High school, Slatina, Olt, Romania.
My idea is a vehicle with rubber engine.
For bilding this car I needed: a plastic bottle (0,5 l), 4 plastic jar lids (two big and two little), a piece of elastic, screws and a thin sheet iron.
I cut out the plastic bottle 4 cm so that the diameter remain constant. The thin sheet iron must have a rectangular shape, 8 cm in length and 1 cm width.
I made 3 holes in sheet iron, one in the middle and two at 0,5 cm from each extremity. Then I bent both ends.
I fixed in the middle of sheet iron a screw with the other end in the plastic bottle.
The axis of fore wheels I made it from a nail introduced in the end holes of rectangular sheet iron.
For the axis of back wheels I made two holes in the plastic bottle.
One end of elastic piece is bound to the axis of back wheels and the other is fixed in the bottle cork.How works:
On put the vehicle on the table and on pull back so that the elastic strip wrap up to the axis of back wheels. When on let vehicle go, stand out of the way!
For this vehicle come true, I asked jar lids of my mother (for wheels). Besides I drew in front of my vehicle the sign from Mercedes.
How it works?
When I am releasing it, it starts to move forward because the elastic force of stretched elastic band, which turn the car’s axle and car’s wheels.
The elastic potential energy, which is stored in the stretched band, is converted to kinethic energy of wheels.
Electrical rotating lamp | To the top |
Materials we needed: support from plastic, cylindrical tube from plastic, electric conductor, socket, electric switch, bulb, lid from a jar, phial glass, copper wire, paper sheets of various colors, adhesive tape.
What we did:
We used the square support from plastic, for a good stability on which we grasped with little screws the cylindrical tube. On the cylindrical tube we fixed with adhesive the electric socket. Through tube we introduced the electric conductor with plug and switch. In the lid of the jar we made radial narrow slits which we bent easy, like a fan. In the lid’s center we introduced the phial from glass and fixed it with adhesive. From many paper sheets of different colors we realized a lamp shade which we glued to the lid with radial narrow slits. On the cylindrical support we fixed a sharp copper wire to the superior end, which wire constitutes the support on which stands the lamp-shade. When the bulb is lighted then the lamp-shade whirls.
Explanation:
When the bulb is lighted, the close by air is warmed because of the heating effect of current and tends to climb. In its way he meets the lid in the shape of fan. This be fixed with the bottom of the sharp copper wire (this way the friction is minimum), he rotate together with the lamp-shade from paper. In order for this device to operate is necessary to be seated on a plane surface so that the lid is suspended in its center and a supplementary friction force doesn’t appear. The greater the electrical power of the lamp, the greater the flow of air it becomes and the stronger the movement for the lamp-shade. The lighted bulb heats the surrounding air. The hot air expands and then rises while the cooler air falls. We say the heat is convected upwards. The lamp shade will rotate like a fan as convection currents move past the lid’s radial holes.
Salt light up the bulb | To the top |
My name is Cosmin and I am 13 years old.
My idea is an electrical circuit to prove that the common salt lead the electric current.
We pour a glass of water and we introduce it in a electrical circuit which have like source the plug from the electric network of the house. In this circuit we insert too a bulb according to the network’s voltage. The ends of the conductor wires inserted in the distilled water will be cleared of insulation.
Like safety measure, only after the electric circuit is ready, we plug in. We will see that the bulb not light on. If we scatter some salt in the water, the bulb light on immediately.
Explanation find by me in the Physics book :
Electric current means transport of electric charges. When electric charges are ions from electrolytes or rarely gases, electric current is called of conduction.
I understand that ions of common salt moves in the water and produces electric current who light on the bulb.
Winter landscape | To the top |
Hello!
I am Marius from Slatina, Olt, Romania.
I am 13 years old.
My project name is "Winter landscape". I decided to make this project for Physics class because I noticed that I could build it easily.
For succeed in this project, mainly it was need a remote control, an electric motor from a toy car and a lot of time.
First I dismantled the little electric motor and the remote control from a toy car. Then I fixed the motor inside of a transparent glass jar lid and I stuck a cardboard propeller on motor axis.
Inside the transparent jar I set an arrangement with a house, two trees, a little man and a lot of polistiren balls. It's a winter landscape.
The remote control have two 1,5 V batteries in serial connection.
The propeller's motion will involve polistiren balls like a snowstorm.
Hydraulic Pump | To the top |
1) Materials
- Two syringes (5 and 10 ml) unuseed in medicine, because can be transmitted some serious diseases.
- Transparent pipe (L = 25 cm). Thhe best choice is a pipe equal in diameter with syringes outgoing orifices.
- Two cardboards (23 x 16 cm)
- Two pieces of wood (15 x 2 x 2 ccm)
- One PVC pipe (l = 12 mm, L = 23 cm)
- White paper
- Selfstick paper
- Coloured water (with ink)
- Two little iron-sheets with hobss at the booth heads; four screws with nuts; two nails; some little naids.
2) Execution Way
Setting the transparent pipe to the syrings (the first you must make an easy warn the both heads). Fill the syringes with coloured water.
Attention: must be not air between the piston and liquid!
Glue one face of a cardboard with selfstick paper; the other face glue white paper. At the down side of this cardboard you must assembled the PVC pipe: assembled the syringes on the cardboard (on the face with white paper) with littles iron-sheets and screws. Between the syringes you may write : the project, who make the project and other things. Glue the second cardboard with selfstick paper on both sides. On this cardboard you must settings the woods, helping by the littles nails. Make a casual hole in each of wood and setting the cardboard hole in each of wood and setting the cardboard with the syringes helping by two nails.
3) How it Works
If you press a piston, you will see the piston from the other going up because the presure force. Looking at the gradation you will see if you push a volume of liquid from a first syringe, the some volume go in the second syringe. The A syringe piston is moving slower than the second syringe piston, because bigger diameter of A syringe.
The Hydraulic Pump function prove the not-compressed of liquids.
The electric circuit | To the top |
My name is Robert. I made an electric circuit made with these components :
-A battery of 4,5 V(volts)
-Two bulbs, B1 and B2 of 3,6 volts and 0,75 amperes
-Two buttons, K1 and K2
-Electric cable
-Support
The electric circuit can be realized very easy by connecting the two consumers (the two bulbs) at the landmarks of the source of energy (the 4, 5 volts battery). In this way, when we shut the first button K1 the effect is the first bulb is lighted, and when we shut the second button K2, the both bulbs are lighted (B1 and B2).
The project is a very easy idea inspired from many electric circuits used first of all at many electric machines and others more complicated.
When the lamp lights, we say an electric current is flowing round the circuit.
In fact, negative electrons are being pushed out of the negative pole of the cell and are drifting slowly round the circuit, from atom to atom in the wire, to the positive pole of the cell. We know now that an electric current is flow of electrons from negative to positive. However scientists marked arrows the opposite way (from positive to negative) like conventional current on circuit diagram.
For an electric current to flow, there must be a complete circuit, with no gaps.
In a series circuit:
a) the same current flows through each component
b) total p.d. = sum of p.d.’s across the separate resistors.
In a parallel circuit:
a) there is the same p.d.’s across each component in parallel
b) total current = sum of currents in the separate resistors.
The moving-coil loudspeaker
The loudspeaker in a radio is using to convert electrical energy to sound energy.
It contains a movable coil attached to a large cone. The coil fits loosely over the centre of a cylindrical permanent magnet so that the coil is in a strong magnetic field.
If a current flows in a direction shown, the coil will move to the right. If the current reverses, the coil moves the opposite way.
As the current (from an amplifier) varies rapidly, the coil and the cone vibrate rapidly.
As the cone vibrates out and in, it produces the compressions and rarefactions of a sound wave.
If the current varies at a frequency of 1000 hertz, then you will hear a note of frequency 1000 hertz.
The same apparatus can be used in reverse as a moving-coil microphone.
The water mill(1) | To the top |
We are Alina and Nicoleta from“Nicolae Titulescu” High school, Slatina, Olt.
We made an experimental device, named “The water mill”. The water mill was built by people, for simplify the hand’s work.
Materials:
cardboard, matches, a plastic bottle, a tray of plastic material, a syringe pin, a propeller, sheet iron, glue, lath, cork, a nail.
How we proceeded?
We cut four equals cardboards and we glue to the back of cardboard laths. We made a hole in the middle of cardboard, where we introduced a screw. We must to turn about the syringe pin to the screw, where we put the propeller. We glue the four cardboards to obtain the little house’s walls and we glue a little bit of sheet iron, like a little table. We made a circular roof, for the house with glued matches.
We holed the cork of the bottle and we made an orifice for the air. We imagined, in this way, the fall of water. We made the support of the bottle so that the place where is the bottle to be inclined in front.
It was a very meticulous experiment, but the result merit the effort.
Explanation:
The water has a potential energy, because it falls from a big height. This energy is transformed in kinetic energy, of the propeller. In nature, the energy don’t disappear, but is transformed from a form, to another.
How it Works?
When an object is lifted to a high place, it has stored energy,called gravitational potential energy.This energy it can give aut if it falls down.
All moving objects have movement energy, called kinetic energy. Energy can be changed from one kind to another. When this happens, the amount of energy stays the same, because energy cannot be created or destroyed. This fact is called the Principle of Conservation of Energy. In the case of water mill, the gravitational potential energy of the water is converted to the kinetic energy of the falling water and the propeller.
The water mill(2) | To the top |
The water mill was one of the first machinery built by man to replace the force of arms and animals.
To build the water mill we need 4 (four) pieces of wood. Two of them have the diameter of 15 cm long and 16 cm shortness and the other two have the diameter of 15,5 cm long and 15 cm shortness. Then we fix the pieces of wood in the box of wood like a square. The roof of the mill is made of two pieces of wood with the diameter of 14 cm high and 16 cm long. Next I took a cork and I made a hole in it. Then I made 4 cuts to fix the pallets from 2 telephone- cards, after that I took a borer and made a hole in the water.
The mill fixing the wheel with a nail of 20,5 cm. To realize the turbine of the mill I’ve taken a plank with the diameter of 8 cm wide and 25 cm long. Then I cut an iron sheet like a rectangle and I put the sheet to the plate. After I fixed the plate, I take 2 small planks with the diameter of 6 and 5,5 cm high and 2 cm wide which I fixed into the same board.
For the support to have stability I made two pieces of wood almost square with 9,5 cm diameter, 8,5 cm high and 5,5 cm wide. Next I took a water bottle from plastic of 1,5 l and I filled it with water. Then I made a hole in the rear of the bottle. I made a hole in the bottle cork.
To work I filled the bottle and I put it on the support with the hole up for the air to enter freeing this hole the water could flow from the bottle. I put in motion the water mill.
This project is made and tested by Enache Ionela, that’s me , and by Enache Florea, my father.
Copper-plating an object | To the top |
Hi! I’m Madalina and I want to present you a device for copping that I created with my father and Ancuta.
Materials:
- a jar with plastic lid;
- a 4,5 V battery;
- two connecting wires;
- a thick insulated copper wiree, 10-15 cm long, or a copper electrode;
- copper sulphate solution;
>
- some coins.
First I scraped the insulation of the copper wire and the ends of the connecting wires. Because the copper wire was too big I put it around a pencil like a resort I made 2 holes in the lid. In one of the holes I get out one end of the copper wire and I connect it on the positive pole of the battery. The cathode is a coin connected to the negative pole of the battery. I closed the circuit and the coin becomes plated with cooper.
Liquids which conduct electricity are called electrolytes.
When electricity is passed through a liquid, it may change the liquid – this is called electrolysis.
The electricity has a chemical effect on the electrolyte splited into positive and negative ions, by drift them to electrodes (anode and cathode).
The copper wire is connected to the positive pole of the battery and is called anode (+). The coin is connected to the negative pole of the battery and is called cathode (-).
A molecule of copper sulphate is formed from 1 atom of copper Cu, 1 atom of sulphur S and 4 atoms of oxygen O.
When copper sulphate is dissolved in water, we believe that it splits into two charged parts called ions: a positive ion of copper and a negative ion of sulphate.
When electricity is passed through the copper sulphate solution, as unlike charges attract, this Cu ions drifts toward the negative cathode where it gains 2 electrons to become an atom of copper plating on the cathode (the coin or any clean metal object). The sulphate negative ion drifts to the positive anode.
Uses of electrolysis
1. Electroplating
In a similar way to copper plating, objects like spoons can be silver- plated if they are used as the cathode of an apparatus containing silver.
Chromium plating for cars and bicycles is achieved by a similar method.
2. Refining copper
In this experiment, the copper transferred to the cathode was very pure even though the anode may have been made of impure copper.
This process is used to produce pure copper for electric cables.
3. Manufacture of sodium and aluminum
These metals are obtained by electrolysis of common salt for sodium and of aluminum oxide for aluminum.
The telephone network | To the top |
Materials we needed:
a cardboard box;
a loudspeaker;
2 blades;
a black lead from a pencil;
a battery.
What we did:
On one side of the cardboard box we cut two narrow slits with a knife. We introduced the blades in each slit. One blade is connected to a pole of battery and the other to the loudspeaker. Another pole of battery is also connected to the loudspeaker. So we have a circuit with a battery, a loudspeaker and two blades.
When we place the lead on the two blades, the telephone network is complete.
When the lead is off we have a gap in the circuit.
If we move the lead on the two blades we must hear a sound from the loudspeaker
.
With this experimental device we won a mention to the first edition of Science Fair contest organized by Comenius 3 "Hands on Science" network in Bucharest.
Explanation:
Sound is produced by vibrating objects. The air in the box vibrates as the lead vibrates, and so does the box.
This fact produces varying electric currents. As the current varies, the loudspeaker vibrates and produces a sound.
The volcano | To the top |
The latest news we have heard from the local radio/TV informed us about a volcano in the Hawaii Islands which is erupting periodically. What is surprising is the fact that its incandescent lava is thrown at a very high distance (height). At the beginning of the February, this year, the lava began again to quit from the bottom of the Earth and it drains in the Pacific Ocean. This phenomenon represents an extraordinary show for tourists in the islands.
We made a model of this volcano for the next experiment: we put cubes of sugar (that contain carbon, hydrogen and oxygen) in aluminum thin above a spirit. While the sugar is warming it changes its color, from white to brown and from brown to black. After that it is changed in an ashy material, “the lava”. It drains in an inclined, cylindrical tube. We put a bowl of water, “the Pacific Ocean” at the end of the tube.
In a similar way we have explained the way the volcano stones are build-up, because from the lava which comes out on the surface and cools are formed basalt, granite and ponce stone.
Batiscaf | To the top |
- I realised the Batiscaf in one hour. It may be used like application to
The Pascal Law.
- I used the materials like can pllastic and transparent, test- tube with cork.
- Achievement: In the cork to testt- tube make one orifice very small with two millimeters size. Now I fill the con with water and insert the test- tube and close the con.
- The function- principle is: whenn press frame con, test-tube go up.
- I worked lonely to the project.
Yet I worked to it with pleasure and I hope to make another, because they are very interesting and when you make many applications you can learn much about physics.
Pressure is transmitted throughout a fluid (liquid or gas) and acts in all directions (Pascal’s law). When the bottle is pressed, thewater is forced in the test tube through the cork’s little hole and the air from the test tube is squeezed to a smaller volume. On the test tube act two forces: the weight of the object and the upthrust (Archimede’s force). For a floating object, the upthrust equals the weight of the object.
In our case, the volume of the water from the test tube increase and so it’s weight until is bigger than the Archimede’s force. Thank to this fact, the test tube is sinking.
If the bottle is released, the water goes out, its (liquid or gas) diminishes and the test tube returns to the initial position.
When an object is into some fluid (liquid or gas), (there are three cases), there are two forces who acts on it: weight and Archimede’s force (upthrust).
There are three cases:
1) The weight is bigger than Archimede’s force and the object will sink;
2) The weight is equal with the Archimede’s force and the object stay will;
3) The weight is smaller than Archimede’s force and the object will float up to the surface.
The drive force | To the top |
Hello! My name is Andrei Alexandru, I am 13 and I` m a schoolboy at the ” Nicolae Titulescu ” High school, in the Vll D class.
I` ve manufacted a car.
1. Components:
-a car;
-a motor;
-a bulb;
-a remote control;
-some wires;
-a plastic bottle;
-a meernchaum;
-adhesive;
-batries;
2. How I proceeded:
- first time I` ve got the wheels from a old car and I put them a bottle;
-I`ve bought a car with remate coontrol,this car had a bulb;
-I took the bulb and I put him at the bottle lid
-at the bottle I put a piece of meeernchaum fore the appearance.
This toy help you to understand the drive force. I hope this is working.
The car by sea and the boat by land | To the top |
My name is George Marius and I am 14 years old.
This project I made it by myself and I needed these materials:
-a plastic bottle
-a motor car
-a 1,5 V battery
-4 wheels
-pieces of wood
I made with a nail 4 holes, 2 on the side and 2 on the other side of the bottle.Then I glued the little pieces of wood on the wheels and I introduced the wheels in the holes.On cut the up side of the bottle when we can fix the motor car to the back wheels and the battery.
The motor car, the wheels and the battery must be connected. The electric current goes from the 1,5 V battery to the motor car who spin itself and who spin the wheels to his turn, so my car will travel over land and sea.
At the back of the car is a boat that can travel over sea and land.For building it I needed a boat from plastic or wood to wich I put 4 wheels, so I invented the car by sea and the boat by land.
The oil drop | To the top |
Hello! My name is Mariana Cristina, I am 12 years old , I` m a schoolgirl at the Vocational National College” Nicolae Titulescu ”. To make this project, the following materials have been necessary:
-a few oil drops;
-alcohol;
-very concentrated water solution with kitchen salt.
The fulfilment of this project has been :
• Fill the glass with water to a half, add the oil drops.
• They will float at the surface.
• Pouring alcohol, they come down inside this.
To bring the water drops at the surface, pour water solution with kitchen salt and you’ll notice how the oil drops return to the surface.
For this project I needed two hours and it was very difficult for me.
A hovercraft | To the top |
My name is Mihai, I'm 12 years old.
Materials for my project: a large tin lid, a cork, a balloon
Way of realisation:
Punch a hole in the middle of a large tin lid.
Drill or burn a hole through a small cork and glue the cork over the hole in the lid.
Blow up a balloon, slide the neck onto the cork and place it on a smooth table. With one little push the hovercraft will go on the table.
Friction is a very common force. Whenever one object slides over another object, friction tries to stop the movement. Friction always opposes the movement of an object. A way of reduction friction is to separate the two surfaces by air. This is how a hovercraft works.
Other ways of reduction friction:
-to polish the surfaces in contactt
-to lubricate them with oil
-to have the object rolling insteaad sliding
-cars, planes and rockets are streeamlined to reduce friction with the air; even so, rockets can get very hot when they enter the Earth’s atmosphere.
Although it is often a nuisance, because it converts kinetic energy into heat and wastes it, friction is also very useful. Our lives depend on the friction at the brakes and tyres of cars and bicycles. Air friction slows down the parachute of a falling man, so that he can land safely. You are able to walk only because of friction with the floor (try walking on wet ice!). Knots in string and the threads in your clothes are held together by friction. Nails and screws are held in wood by friction. If all friction suddenly disappeared, our life might turn into a nightmare.
Self-propelled boat | To the top |
I am Adina. I am 13 years old.
What I needed:
a piece of expanded polystyrene, a big yoghurt carton, a straw about 7 mm in diameter, a little piece of wood, matches, glue, colored paper, a toothpick.
What I did with these materials:
I cut from the piece of expanded polystyrene a pentagon like in the picture. I calculate the dimensions of the boat depending on the diameter of the yoghurt carton. You can see in the picture the place and the diameter of the yoghurt carton.
I made to the base of the lateral wall of the carton and I introduced the straw which I glued horizontally.
The carton must be fixed with glue on the piece of polystyrene, and in front of the carton I glue the piece of wood for balance.
I made the colors from the paper and the toothpick and I glued to the wood piece. When the yoghurt carton is filled with water and the boat is on the surface of a basin, the water from the carton runs down by the lateral straw and the boat goes forward.
Ages 15 -16
Hydrostatic pressure | To the top |
Hello! We are Ana-Maria Neghina and Catalin Medeleanu(16 years old) and we present you "Hydrostatic pressure".
Work’s theory:
Because of its weight, a liquid exerts pressing forces to the walls of the vessel. A liquid at rest exerts pressing forces to the surface of any object which is in contact with. These forces are perpendicular to the surfaces that the forces are exerted. The pressure, which is exerted to a certain level inside a liquid and which depends on the weight of the liquid column over this level, is called hydrostatic pressure.
Inside a liquid, the hydrostatic pressure increases with depth.
To a certain point of the liquid, the hydrostatic pressure has the same value in all directions (it doesn’t depends on the surface orientation, where the pressure is exerted).
Pressure is the same in all the points on an horizontal surface.
In the points which are situated to the same depth, in different liquids, hydrostatic pressure depends on the nature of the liquid and they are proportional with the density of the liquid.
Objective:
In this experiment we investigated the factors on which depends hydrostatic pressure.
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling, 250 ml plastic beaker, 340 mm rubber tube,
water manometer, 25 ml measuring cylinder, plastic clip, water colorant, funnel.
Way of work:
Set up the experiment as shown. For that you may follow all the steps shown in the movie by Ana-Maria and Catalin. The total length of column of colored water from manometer must be 5 cm. Fill 4/5 of 250 ml beaker with water. Place one end of the rubber tube in manometer and the other end into the funnel. The open end of the funnel is gently lowered into the beaker.
The levels of the colored water in the manometer are changed. The pressure can be found (in “centimeters of water”) by measuring the height marked “∆h”.
Pressure increases with depth.
Then move the funnel horizontally in the water and observe the effect on the manometer.
Optionally, you can change water with another liquid and see what is happened.
Here are our results:
| h(cm) | p1(Pa) | ∆h(cm) | p2(Pa) |
| 0,5 | 49 | 0,5 | 49 |
| 1 | 98 | 1 | 98 |
| 1,5 | 147 | 1,3 | 127,4 |
| 2 | 196 | 1,8 | 176,4 |
| 3 | 294 | 2,7 | 264,6 |
Conclusion:
Inside a liquid, the hydrostatic pressure increases with depth.
To a certain point of the liquid, the hydrostatic pressure has the same value in all directions (it doesn’t depends on the surface orientation, where the pressure is exerted).
Pressure is the same in all the points on an horizontal surface.
In the points which are situated to the same depth, in different liquids, hydrostatic pressure depends on the nature of the liquid and they are proportional with the density of the liquid.
Adhesion forces | To the top |
Hi, we are Florin Titoveanu and Mihai Iliuta (16 years old), we are both Romanian and we are studying at “Nicolae Titulescu” High school, Slatina. We present you "Adhesion forces".
Work’s theory:
A distinction is usually made between an adhesive force, which acts to hold two separate bodies together (or to stick one body to another) and a cohesive force, which acts to hold together the like or unlike atoms, ions, or molecules of a single body. The adhesion of water to glass is stronger than the cohesion of water. Hence, when water is spilled on a clean glass surface it wets the glass and spreads out in thin film. On the other hand, the cohesion of mercury is greater than its adhesion to glass. Therefore, when mercury is spilled on glass it forms small spherical droplets or larger flattened drops.
The difference between the adhesive and cohesive properties of water and mercury explains why the meniscus of water curves upwards and that of mercury curves downwards when these liquids are poured into clean glass vessels.
Objective:
In this experiment we investigated the adhesion forces between molecules of two different substances.
Needed materials:
clamps, a plastic disk, a spring balance, aluminum stand with rail, plastic stands, a string three cm long, sliding clamps with three holes, 330 mm aluminum rod, double coupling, large beaker.
Way of work:
On assemble the experimental device like in the picture. Fill the large beaker with water. Lower the red plastic disk slowly into the water so that it touches water’s surface in a perpendicular way. Then raise gradually the red disk so that be able to measure with a spring balance the necessary force to take it out from water.
Repeat ten times and put the results in a table.
| F(N) | ∆F(N)=|F-F medium| |
| 0,65 | 0,001 |
| 0,63 | 0,021 |
| 0,68 | 0,029 |
| 0,64 | 0,011 |
| 0,67 | 0,019 |
| 0,66 | 0,009 |
| 0,65 | 0,001 |
| 0,69 | 0,039 |
| 0,64 | 0,011 |
| 0,60 | 0,051 |
∆F is the absolute error.
We may calculate the medium force:
F medium= (0,65+0,63+0,68+0,64+0,67+0,66+0,65+0,69+0,64+0,60)/10=0,651N
(∆F) medium=(0,001+0,021+0,029+0,011+0,019+0,009+0,001+0,039+0,011+0,051)/10=0,0192N
F=F medium +/- (∆F) medium
F=0,651 +/- 0,0192 N
Conclusion:
Between the water surface and the disk surface is an attractive force called adhesion force. This force depends on the nature of materials into contact.
Surface tension | To the top |
Hello! We are Ilinca Mihaela and Pietrisi Ilona(16 years old) and we present you "Surface tension".
Work’s theory:
In a liquid, the molecules are moving more slowly and are held together more closely than in a gas, by forces between the molecules. These forces make the liquid have a definite size, although it can still change its shape and flow.
All phenomena in connection with the surface of a liquid are called surface phenomena. Inside the liquid, each molecule is equally attracted in all direction by molecules from its action sphere, to give no resultant force at all. But on the surface of liquids, things are different because each surface molecule from the liquid interacts with its similar neighboring molecules and with air molecules. Forces liquid-gas is weaker than forces liquid-liquid. So, in this case we have a vertical downwards resultant force.
This forces cause an internal pressure who explains why the liquids are incompressible.
In liquids, molecular attractive forces between surface molecules have a resultant force named “force of surface tension”. This causes a “skin” or surface tension. The tension tries to reduce the surface area. This is why bubbles are spherical (as this shape has the smallest area for a given volume).
Objective:
In this experiment we observed the surface tension in liquids.
Needed materials:
large beaker, two small aluminum pieces.
Way of work:
Fill a large beaker with clean water. Drop the two light aluminum pieces in water. Then dry them and carefully float them on water. Watch them. Press on the pieces with your finger (first lightly, then strongly) and notice the result.
Conclusion:
When we drop the two light aluminum pieces in water from a small height, will sink. But when we dry and carefully float them on water, will float without getting wet.
This experiment shows that there is a surface tension on the surface of liquids. This is due to the forces attracting each surface molecule to its neighboring molecules.
There is tension because the molecules on the surface are slightly farther apart (like the molecules in a stretched elastic band). This force of attraction between molecules of the same substance is called cohesion. This explains why a light metallic object with a density bigger than water’s density will float. If we press our finger on the object first lightly, then strongly, it will sink.
Transmission of the pressure throughout the liquid | To the top |
Hello! We are Gusatu Bogdan and Iacobescu Daniela (16 years old) and our experiment's name is "Transmission of the pressure throughout the liquid".
Work’s theory:
Pascal's Law (also called Pascal's Principle) says that "changes in pressure at any point in an enclosed fluid at rest are transmitted undiminished to all points in the fluid and act in all directions." This sounds rather overwhelming at first, so let's break it down a bit.When it says "enclosed fluid," that means that in order for Pascal's Law to be true, you have to be looking at a liquid in a closed container.Pressure is basically a fancy word for how much something pushes on its container and on things in it. For example, air pressure is how hard air pushes on things. When you pump more and more air into your bike tire, you're increasing its pressure. If you increase its pressure too much, then it will be pushing out more than the plastic is capable of pushing in, and your tire will explode. Water pressure works the same way. Pascal’s principle put more simply, basically means that an incompressible fluid transmits pressure. This is the basis to hydraulic lever. In a hydraulic lever, for example, you apply a force to the left-hand piston over a given area, this force is then transformed in to a pressure which is transmitted through the hydraulic fluid or oil. This pressure then transforms back in to an output force over another given area for the right-hand piston.
Objective:
In this experiment we investigated transmission of the pressure throughout liquids.
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling, 15 mm plastic clip, two 10 ml plastic syringes, a 200 mm rubber tube, 250 ml plastic beaker.
Way of work:
Assemble all materials like in the picture.
First plastic syringe is full with water and the second is empty, with the piston is down.
The two of them are connected by a rubber tube.
Push the piston of full syringe and then push the piston of empty syringe.
Conclusion:
Pressure is transmitted throughout the liquid.
This is the Pascal’s Law.
Capillary tube | To the top |
We are Marcu Florina and Ispas Adriana(16 years old) and we present you "Capillary tube".
Work’s theory:
A glass tube of a very fine bore (some millimeters) is called a capillary tube. Capillarity results from a combination of adhesion and cohesion. On dipping the tube in the water, alcohol or any other liquid which wets glass it is noticed that the liquid rises in the tube to a height of several centimeters. Mercury, however, gives a capillary depression. The adhesion of water to glass is stronger than the cohesion of water. On the other hand, the cohesion of mercury is greater than its adhesion to glass. This also explains why the meniscus shape at the top of water is curved upwards. With mercury there is a capillary fall. This is because the adhesion (between mercury and glass molecules) is less than the cohesion (between mercury molecules).
The rise is h=2σ/ρg r (Jurin’s Law)
Objective:
In this experiment we investigate the capillary tube.
Needed materials:
aluminum stands with rails, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling, beaker, capillary tube
Way of work:
You need one narrow capillary tube. Place the clean glass tube so that it dips into the beaker of colored water. Watch the water rise up the tube. This is called capillary rise:
h=2σ/ρg r (Jurin’s Law)
We measured h=1 cm and we calculated r=2σ/ρg h, where
σ=72,8•10-3N/m
ρwater=1000kg/m3
g=9,8m/s2
Then r=1,48 mm.
The effect of a gas force | To the top |
We are Calta Andra and Pruna Lucian(15 years old) and we present you "The effect of a gas force".
Work’s theory:
Newton noticed that forces were always in pairs and that the two were always equal in size, but opposite in direction. He called the two forces action and reaction.
Newton’s third Law of motion is: action and reaction are equal and opposite.
Forces are vectors. Vectors have size and direction.
The momentum of an object depends on its mass and its velocity.
In fact,
Momentum = m•v
Momentum is a vector quantity. It is measured in units of kg•m/s.
The Principle of Conservation of Momentum is:
When two more bodies act on each other, their total momentum remains constant, providing there is no external force acting.
Total momentum before=Total momentum after
0 =m1•v1 – m2•v2
m1•v1 = m2•v2
In this experiment we investigated Newton’s third Law and the Principle of Conservation of Momentum.
Needed materials:
aluminum stands with rails, plastic stands, double coupling, plastic clip, balloon, trolley, valve
 |  |
Set up the experiment as shown. Blow up the balloon and fix it on the trolley, then release it.
The balloon and the trolley move forward, because the escaping air is rushing backwards.
In the same way, jet engines and rockets move forward, because on the hot gases rushing out of back
Examinations of the results:
These are all examples of Newton’s third Law and of the Principle of Conservation of Momentum.
When neck is tied, forces in the balloon cancel, but when neck untied, force forward. The pairs of forces are:
The force of the air on the balloon (downwards)= The force of the balloon on the air (upwards)
The force of the air on the balloon to the left)= The force of the balloon on the air (to the right)
Total momentum before =Total momentum after
0 =m1•v1 – m2•v2
m1•v1 = m2•v2
 neck tied (forces cancel) |  escaping air (force forward) |
The Inclined Plane | To the top |
Hello! We are George Grosu and Corina Lungu(16 years old) and our experiment's name is "The Inclined Plane".
Work’s theory:
A ramp, a slope and a hill are examples of inclined planes.
When we weigh a small trolley with a spring balance, we measure the load of the trolley.
We pull it up an inclined plane, we measure the effort.
The effort is smaller than the load. The smaller force always moves the longer distance -in this case, the effort has to move the full length of the slope while the load moves a shorter distance vertically.
This means that:
Velocity Ratio (V. R.) = distance moved by the effort along the slope / distance moved by the load vertically (it does not depend on friction)
The inclined plane helps us to magnify the effort force. To see how much is magnifies the effort force, we calculate the mechanical advantage:
Mechanical advantage (M. A.) =load/effort
(it depends on friction)
We represent an inclined plane by a right angled triangle:
The elements of an inclined plane are:
- height h
- length l
- angle α
-V. R. = l/h
- M. A. =G/F
The necessary force for the trolley, to run up at constant velocity (no acceleration), without friction, on an inclined plane is:
F = Gh/l
% Efficiency = ( M. A./ V.R.) x 100%
= work got out / work put in x 100% (it depends on friction and is always less than 100%)
Objective:
In this experiment we investigate the inclined plane.
Needed materials:
aluminum stands with rails, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling, S-forms hook, a spring balance, two standard masses of 50g each, plastic clip, a 43 mm pulley, a metallic axle of 80 mm long, clamps, trolley, string
 |  |  |  |
Set up the experiment like in the picture. We fixed the rod on the stand using a sliding clamp with three holes. We putted the spring balance on the rod using a double coupling. Then we connected the spring balance and the trolley using a pulley and a piece of string. The initially height of the inclined plane was 8 cm. We measured the effort for three situations: empty trolley and trolley with a 50 g standard mass. Then we repeated for 10 cm, 12 cm, 14 cm, 16 cm vertical height. We also measured the weight of the empty trolley (0,97 N) and the slope’s length(36 cm).These results were obtained:
| h(cm) | m(g) | Gc(N) | Gt(N) | sina=h/l | Gt(h/l)=Gsina | F(N) |
| 8 | 0 | 0,97 | 0,97 | 2/9 | 0,21 | 0,22 |
| 8 | 50 | 0,97 | 1,46 | 2/9 | 0,3 | 0,30 |
| 10 | 0 | 0,97 | 0,97 | 5/18 | 0,26 | 0,31 |
| 10 | 50 | 0,97 | 1,46 | 5/18 | 0,40 | 0,32 |
| 12 | 0 | 0,97 | 0,97 | 1/3 | 0,31 | 0,32 |
| 12 | 50 | 0,97 | 1,46 | 1/3 | 0,48 | 0,36 |
| 14 | 0 | 0,97 | 0,97 | 7/18 | 0,37 | 0,39 |
| 14 | 50 | 0,97 | 1,46 | 7/18 | 0,56 | 0,48 |
| 16 | 0 | 0,97 | 0,97 | 4/9 | 0,42 | 0,41 |
| 16 | 50 | 0,97 | 1,46 | 4/9 | 0,64 | 0,55 |
We observe that, for all vertical heights of the inclined plane, F=Gh/l if m=0 and Gh/l>F if m=50g. The difference is the friction.
Measuring the volume of an irregular object | To the top |
We are Lungu Cristina and Dosinescu Ion(15 years old) and we present you " Measuring the volume of an irregular object".
Work’s theory:
The volume of an object is its occupied place in space.
The volume of a regular object is:
V=length x breadth x height
The volume of a substance of regular shape, e.g., a rectangular bar or sphere may be calculated from measurements. The volume of an irregular solid, e.g., a piece of coal may be found using a measuring cylinder.
The SI unit of volume is the cubic meter, but when volume is being measured in the laboratory it is generally most convenient to work in cubic centimeters.
Objective:
measuring the volume of an irregular object
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling, 25g and 50g mass with double hook, measuring cylinder, a metallic axle of 80 mm long, clamps, string
Way of work:
Fill the measuring cylinder with 15 ml water. Gently lower the 25g mass with double hook into the water and note the new reading. The difference gives the volume of the mass. Repeat the experiment with a 50g mass and note the reading.
Our results are in the next table:
| No. | Mass(g) | V1(ml) | V2(ml) | V(ml)=V2-V1 |
| 1 | 25 | 15 | 19 | 4 |
| 2 | 50 | 15 | 21,5 | 6,5 |
Examination of the results:
When an object is lower into the water, the water level rises. The object volume is equal with the volume of displaced water.
The manometer | To the top |
We are Andreana Oana and Sandulescu Elena(16 years old) and we present you " The manometer ".
Work’s theory:
The manometer is an instrument for measuring the pressure of gas.
The manometer consists of a U-tube containing some liquid, usually water. When both arms are open to the atmosphere, the same atmospheric pressure is exerted on the water surfaces A and B, and these are at the same horizontal level. In order to measure the pressure of the gas supply in the laboratory, the side A is connected to a gas-tap by a length of rubber tubing. When the tap is turned on, the gas exerts pressure on the surface A, with the results that the level B raises until the pressure at C on the same horizontal level as A becomes equal to the gas pressure.
Thus,
pressure of gas = atmospheric pressure + pressure due to water column BC, marked “h”
It follows that the excess pressure, in Pa, of the gas above that of the atmosphere is given by the pressure of the water column and is therefore equal to ρgh.
Objective:
the study of a manometer
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling, measuring cylinder, clamps, an absorption bottle, lid, manometer, rubber tube, blue colorant.
Way of work:
Put plastic stands to the aluminum stand with rail. Fix sliding clamps with three holes above the aluminum rail, then aluminum rods. Using double couplings and plastic clips arrange the manometer and the absorption bottle. Insert one end of the rubber tube 5 mm in upper side of the absorption bottle and the other end in the horizontal side of the U-tube. Fill the manometer with colored water so that the horizontal level is the same in both arms. You must avoid formation of air bubbles, otherwise repeat the procedure. Now, close the side tube of the absorption bottle with a little lid. Seize the absorption bottle with hand so that your big finger exerts a pressure to the cork of a bottle. See the effect of the pressure on the both water levels.
Examination of the results:
The water columns close the air from the absorption bottle. If pressure is exerted on the cork by hand, the inside air is compressed and pushes up the water in the U-tube. The water difference in level is a measure of the difference in pressure of the two sides of the manometer.
Higher pressure/ lower pressure | To the top |
We are Voinic Simona and Biruta Andra(16 years old) and we present you " Higher pressure/ lower pressure ".
Work’s theory:
The manometer is an instrument for measuring the pressure of gas. When both arms are open to the atmosphere, the same atmospheric pressure is exerted on the water surfaces and these are at the same horizontal level. When pressure on the surface A is different from the surface from the pressure on the surface B, the water level is not the same in manometers arms.
Objective:
study of the effect of a higher and a lower pressure on the columns level of water in a manometer
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling, measuring cylinder, clamps, an absorption bottle, lid, manometer, rubber tube, blue colorant.
Way of work:
Assemble all materials like in the picture. Pool the syringe piston. See the effect. Push the syringe piston. See the effect. Repeat these movements of many times and notice what happens.
Conclusion:
When the pressure is higher than the atmospheric pressure, then the column of water goes down. When the pressure is lower than the atmospheric pressure, then the column of water goes up.
Communicating tubes | To the top |
We are Dragnea Oana and Mogos Mariana(16 years old) and we present you " Communicating tubes ".
Work’s theory:
When water or any other liquid is poured into the communicating tubes shown in fig.1 it stands at the same level in each tube. This illustrates the popular saying that, “water finds its own level”.
When the liquid is at rest in the vessel the pressure must be the same at all points along the same horizontal level, otherwise the liquid would move until the pressures were equalized. The fact that the liquid stands at the same vertical height in all the tubes whatever there shape confirms that, for a given liquid, the pressure at a point within it varies only with the vertical depth of the point below the surface of the liquid.
Objective:
the study of the communicating tubes
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, clamps, rubber tube, two communicating tubes, plastic beaker, support rings.
Way of work:
Put plastic stands to the aluminum stand with rail. Fix sliding clamps with three holes above the aluminum rail, then aluminum rods. First, on arrange the two communicating tubes with support rings at the same horizontal level. A rubber tube connects them. Fill one tube a half with water. Surfaces are all at same level. We measured this level with a rule. Then, lift up a tube by sliding its support ring along the rod. See the effect on water level in each tube.
Conclusion:
The liquid stands permanently at the same height in all communicating tubes whatever their shape and position. We can consider one vessel instead of many communicating vessels with one free surface.
Measurements of density | To the top |
We are Ditu Mihaela and Bucica Mihaela Simona(16 years old) and we present you " Measurements of density".
Work’s theory:
One often hears the expressions “as light as a feather” and “as heavy as lead”. Equal volumes of different substances vary considerably in mass. In Physics we refer to the lightness or heaviness of different materials by the use of the word density.
The density of a substance is defined as its mass per unit volume.
The symbol used for density is the Greek letter ρ (rho).
Thus,
Density=mass/volume
or in symbols ρ=m/V.
The SI unit of density is the kg/m3.
Importance of density measurements is essential for calculating the strength required in foundations and supporting pillars of bridges, flyovers and other structures. Chemists often make a density determination as a test of the purity of a substance.
One way of finding the density of a substance is to take an object and measure its mass and volume. The density may then be calculated by dividing the mass by the volume.
Objective:
measuring the density of an object
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, clamps, balance spring, clips, measuring cylinder, a metallic axle of 80 mm long, metal cylinders, string
Way of work:
On assemble the experimental device like in the picture.
On measure the volume of metal cylinders (Al, Fe, Cu, Pb, Zn, brass) by sinking in a measuring cylinder. The mass of cylinders is found by weighing in air (objects must be dry!).
These results were obtained:
| Material | Al | Fe | Cu | CuZn(brass) | Pb | Zn |
| V(cm3) | 2,5 | 2,5 | 2,5 | 2,5 | 2,5 | 2,5 |
| m(g) | 6,12 | 18,36 | 21,43 | 19,39 | 26,53 | 16,32 |
| m/V(g/cm3) | 2,44 | 7,34 | 8,57 | 7,75 | 10,61 | 6,52 |
Conclusion:
Density is mass per unit volume.
All metal cylinders have the same volume. Different substances have different densities. For an homogeneous object, its density is the same at any point.
Stretching a spring | To the top |
We are Calina Alexandra and Dumitru Relu(16 years old) and we present you "Stretching a spring ".
Work’s theory:
Whenever we are pushing or pulling, lifting or bending, twisting or tearing, stretching or squeezing, we are exerting a force.
Force can :
a) change the speed of an object
b) change the direction of movement of an object
c) change the size or shape of an object.
Objective:
In this experiment we will find out how forces change the length of a spring.
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, clamps, spring, clips, masses with double hook, a metallic axle of 80 mm long, double coupling
Way of work:
On assemble the experimental device like in the picture.
We will need several masses with double hook of 25g, 50g, 75g, 100g, 125g and 150g. First measure the original length of the spring. Hang one weight on the spring and measure the extension ∆l(cm) of the spring. Then hang another weight and measure the extension each time (from the original position).
We putted the results in the next table:
| Mass(g) | 25 | 50 | 75 | 100 | 125 | 150 |
| F(N) | 0,25 | 0,49 | 0,74 | 0,98 | 1,23 | 1,47 |
| l(cm) | 14,9 | 16,4 | 18,3 | 20,3 | 22,2 | 23,1 |
| ∆l(cm) | 1,8 | 3,3 | 5,2 | 7,2 | 9,1 | 10,8 |
| F/∆l(N/cm) | 0,14 | 0,14 | 0,14 | 0,14 | 0,14 | 0,14 |
We considered that G=mg, where g=9,8m/s2 and the original length of the spring is 13,1 cm.
Conclusion:
Whenever we are exerting a force to a spring, results an extension of it. F/∆l is a constant(0,14N/cm) which depends on the substance of the spring.
Hooke’s Law | To the top |
My name is Alin Troceanu, I am 16 years old and I present you " Hooke’s Law".
Work’s theory:
Forces or weights are often measured by means of a spring balance. The principle underlying the spring balance was first investigated in the seventeenth century by Robert Hooke. He showed that when a spring is fixed at one end and a force is applied to the other, the extension of the spring is proportional to the applied force, provided the force is not large enough to stretch the spring permanently.
This is called Hooke’s Law.
The value of the force for which the extension is such that, on the removal of the force, the spring fails to return to its original length and begins to stretch permanently is called the elastic limit.
Objective:
Verify Hooke’s Law
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, spring balance, clamps, masses with double hook, a metallic axle of 50 mm long, double coupling
Way of work:
Put plastic stands to the aluminum stand with rail. Fix a sliding clamp with three holes above the aluminum rail, then the aluminum rod. Using a double coupling a metallic axle and two clamps, held vertically the spring balance. Hang 25g weight on the spring balance and note the extension ∆l(cm) and the force F[N].
A second set of readings is taken for 50g standard mass, then for 75g, 100g and 125g. The readings should be entered in a table as shown:
| m(g) | 25 | 50 | 75 | 100 |
| F(N) | 0,25 | 0,5 | 0,75 | 1 |
| l0(cm) | 4 | 4 | 4 | 4 |
| l(cm) | 6,5 | 9,3 | 11,5 | 14,4 |
| ∆l(cm) | 2,5 | 5,3 | 7,5 | 10,4 |
From our results, we plotted a graph of extension ∆l(cm) against load F(N).
Examination of the results:
A straight line through the origin of the graph confirms that the extension is directly proportional to the stretching force . This is Hooke’s Law. It only applies to the straight part of the graph. Such a graph is called a calibration curve for a spring.
Archimedes’ Principle | To the top |
Hi, we are Balan Ionela Daniela and Albisoru Ioan Fabian (16 years old), we are both Romanian and we are studying at “Nicolae Titulescu” High school, Slatina. We present you "Archimedes’ Principle".
Work’s theory:
When a body is wholly or partially immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced.
FA = ρVg
“Fluid” means either a liquid or a gas. When anything is placed in a liquid, it receives an upward force or upthrust, and so it appears to weigh less in liquid than in air. All liquids exert an upthrust like this, because the pressure inside the liquid increases as you goes deeper. This means that the pressure on the bottom on an object is greater than on the top, and so there is a resultant force upwards.
We have three cases:
1) If the object has exactly the same density as the liquid, then it will stay still, neither sinking nor floating upwards, just as the liquid nearby stay still.
FA = G
2) If the object is denser than the liquid, then the same volume will weigh more and it will sink, because the upthrust will not be enough to support it. The resultant force is called apparent weight.
G>FA
Ga = G – FA
3) If the object is less dense than the liquid, the upthrust will make it float up to the surface. The resultant force is called ascension force.
FA>G
Fa = FA – G
Objective:
The experimental study of Archimedes’ Principle
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, clamps, double coupling, string, spring balance, measuring cylinder, metal cylinders
Way of work:
Set up the experiment as shown. Hang the cylinder of iron on the spring balance and measure its weight in air F1 (N). Fill the measuring cylinder 15 ml with water. Then lower the object slowly into the water. How much does it appear to weigh now? Note is new weight in water F2 (N) and the difference in volume ∆V (ml).
Repeat the experiment with cylinders of Cu, Pb, Al and note results in the next table:
| Material | F1(N) | ∆V (ml) | F2(N) | FA(N)=F1-F2 |
| Fe | 0,175 | 2 | 0,15 | 0,025 |
| Cu | 0,2 | 3 | 0,18 | 0,020 |
| Pb | 0,255 | 2 | 0,23 | 0,025 |
| Al | 0,06 | 3 | 0,035 | 0,025 |
Examination of the results:
Archimedes’ Principle is found to be true for all objects immersed in a liquid. The difference between the two readings F1 and F2 is equal to the upthrust FA. The upthrust depends on the density of the liquid and on the volume of liquid displaced. The liquid is the same, water and all metal cylinders have the same volume, so the upthrust FA is also the same.
Friction | To the top |
Hi, we are Gotoi Cristina and Stanila Diana (16 years old). Our experiment is called "Friction".
Work’s theory:
Friction is the name given to the force which opposes the relative sliding motion of two surfaces in contact with one another. It plays a notable part in our daily lives. For example, we are reminded of the importance of friction every time we slip up, on an icy pavement or a polished floor. Walking would be impossible if there were no friction between the ground and the soles of our shoes. Quite often our lives depend on the force of friction in the brakes of an automobile or a railway train. Knots in string and the threads in our clothes are held together by frictions. Nails and screws are held in wood by friction. Air friction slows down the parachute of a falling man so that he can land safely.
A rectangular block of wood placed on a flat surface has a string and spring balance attached to it so that a horizontal force can be applied.
If a gradually increasing force is applied to the block it will, at first, continue to remain at rest since an equally increasing but oppositely directed force of friction F, comes into action at the under surface of the block. At any particular moment, we say that the pull P and the opposing frictional force F are in equilibrium. If we continue to increase the pull P, a stage will be reached when the block just begins to slip. At this point, the friction brought into play has reached its maximum value for the two surfaces concerned, and this is called the static friction.
If the block is pulled along so that it slips at a steady speed we notice that the spring balance gives a reading rather less than the static friction. Sliding friction is, therefore, less than static.
If the simple experiments we have described are repeated with various weight on the block it is found that both the static and the sliding friction are increased roughly in simple proportion to the force, perpendicular to the surfaces , which is pressing them together.
However even highly polished objects look rough trough a microscope, so there is always some friction (as the lumps on one object catch and stick to the lumps on the other object).
Frictional forces only act when two object are in contact.
A way of reducing friction is to have the object rolling instead of sliding. This is what happens with ball bearings.
Objective:
Observe static, sliding and rolling friction.
Needed materials:
S-hook, spring balance, standard masses of 10 g and 50 g each, trolley
Way of work:
S-hook makes the link between the trolley and the spring balance.
The trolley is placed on a flat surface so that it slips on the rougouse surface.
If a gradually increasing force is applied to the trolley it will, at first, continue to remain at rest.
If we continue to increase the pull, a stage will be reached when the trolley just begins to slip. At this point, we notice and note the spring balance reading. This is the static friction FH. If the loaded trolley is pulled along so that it slips at a steady speed we notice the sliding friction FG1.
Then we place a 50 g mass on top of the trolley and we measure the spring balance reading when the loaded trolley just begins to slip, FH1.
Then we put the trolley on its wheels and repeat the experiments with two 50 g masses and with all 50 g and 10 g masses.
Examination of the results:
We putted all results in a table.
| Sliding | m(g) | Static friction FH(N) | Sliding friction FG(N) |
| 0 | 0,1 | 0,1 | |
| 50 | 0,21 | 0,19 | |
| 100 | 0,25 | 0,24 | |
| 150 | 0,35 | 0,32 | |
| Rolling | 0 | 0,07 | 0,03 |
| 50 | 0,15 | 0,05 | |
| 100 | 0,23 | 0,1 | |
| 150 | 0,37 | 0,2 |
On observe that whenever we want an object starts moving we must apply it a force greater than the static friction FH.
If we want that the object keeps moving, the pulling force must be greater than the sliding force FG , FG < FH. If the object is rolling instead of sliding, than Ff < FG.
Lever of type 1 | To the top |
Hello! We are Militaru Alexandra and Tudor Georgiana(16 years old). Our experiment is called "Lever of type 1".
Work’s theory:
Machines help us to apply forces more easily. Essentially, a machine is any device by means of which a force applied at one point can be used to overcome a force at some other point.
A lever is a very common simple machine. The simplest form of lever in common use is a steel rod known as a crowbar, being used to lever up a stone.
The man is exerting an effort force, against a load force (the weight of the stone).
Two factors are involved here , first, the magnitude of force applied, and secondly, the distance of its fulcrum about which turning takes place.
The combined effect of the force and distance which determines the magnitude of the turning force is called the moment of the force.
The moment of a force about a point is the product of the force and the perpendicular distance of its line of action from the point.
Levers are based on the principle of moments:
When a body is in equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments.
A type I lever have the pivot or fulcrum between the effort force and the load.
Objective:
Measure the effort F for a given load G to a type I lever.
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling,S-hook,
spring balance, double-hook wheights, plastic clip, lever, 50 mm metallic axle, clamps.
Way of work:
Set up the experiment as shown. We hanged a 25g and a 50g masses on one end of the lever. To the other end we applied a force F until the lever becomes horizontal. We modified the load arm (a) and notted all results in the next table:
| G(N) | 0,74 | 0,74 | 0,74 | 0,74 | F(N) | 0,74 | 0,49 | 0,36 | 0,24 |
| a(m) | 0,12 | 0,08 | 0,06 | 0,04 | b(m) | 0,12 | 0,12 | 0,12 | 0,12 |
| Ga(Nm) | 0,088 | 0,059 | 0,044 | 0,029 | Fb(Nm) | 0,088 | 0,059 | 0,044 | 0,029 |
Examination of the results:
Whenever we are hanging a load on the lever, we are exerting a turning force.
The moment of load about the fulcrum is G*a.
The moment of effort about the fulcrum is F*b.
The lever is in equilibrium if G*a=F*b.
Lever of type 2 | To the top |
We are Anton Gheorghe and Ilie Silviu (16 years old). Our experiment is called "Lever of type 2".
Work’s theory:
The simplest form of lever of type 2 in common use is wheelbarrow.
This lever have the load between the effort and the fulcrum.
A small effort moves a large load(the force is magnified).
Levers are based on the principle of moments:
When a body is in equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments.
Objective:
Measure the effort F for a given load G to a type 2 lever.
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling,S-hook,
spring balance, double-hook wheights, plastic clip, lever, 50 mm metallic axle, clamps.
Way of work:
Set up the experiment as shown. We hanged a 25g and a 50g masses between the effort and the fulcrum. To one end we applied a force F until the lever becomes horizontal. We modified the load arm (a) like in the table and notted all results in the next table:
| G(N) | a(m) | Ga(Nm) | F(N) | b(m) | Fb(Nm) |
| 0,49 | 0,18 | 0,088 | 0,44 | 0,2 | 0,088 |
| 0,49 | 0,16 | 0,078 | 0,39 | 0,2 | 0,078 |
| 0,49 | 0,14 | 0,068 | 0,34 | 0,2 | 0,068 |
| 0,49 | 0,12 | 0,058 | 0,285 | 0,2 | 0,057 |
| 0,49 | 0,10 | 0,049 | 0,24 | 0,2 | 0,048 |
Examination of the results:
F
Balance | To the top |
My name is Mihai Preda, I am 16 years old and my experiment is called "Balance".
Work’s theory:
A beam balance is used for the measurement of mass.
Most balances are based on the principle of moments:
When a body is in equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments.
The body, whose mass m1 is to be determined is placed in the left-hand pan and standard masses (usually called weights) m2, are added to the right-hand pan to obtain equilibrium. The balance has been constructed so that the distances, d, of the pans from the centre beam bearing are equal.
Thus equating moments
m1gd = m2gd
or
m1 = m2
From this we see that the balance measures mass, not weight, and it is quite independent of the value of g. Furthermore, it will correctly measure mass anywhere so long as the masses concerned possess weight.
Should we want to know the weight of the body we could calculate it by multiplying the mass by the local value of g.
Objective:
measuring the mass of metallic cylinders using a balance
Needed materials:
aluminum stand with rail, plastic stands, sliding clamps with three holes, 330 mm aluminum rod, double coupling, 10 g standard masses, lever arm, pans, cylinder, a metallic axle of 50 mm long, clamps, metallic cylinders
Way of work:
On assemble the experimental device like in the picture.
The method of balance should be used to find the masses of metallic cylinders. We repeated this operation 10 times with each cylinder. The results were recorded in the next table:
| No. | m1 Al (g) | m2(g) | No. | m1 Cu (g) | m2(g) | No. | m1 Zn (g) | m2(g) | No. | m1 CuZn (g) | m2(g) | No. | m1 Pb (g) | m2(g) | No. | m1 Fe (g) | m2(g) |
| 1 | 6,12 | 6,2 | 1 | 21,43 | 20,5 | 1 | 16,32 | 16,3 | 1 | 19,39 | 19,4 | 1 | 26,53 | 26,1 | 1 | 18,36 | 18,3 |
| 2 | 6,12 | 6,2 | 2 | 21,43 | 20,4 | 2 | 16,32 | 16,2 | 2 | 19,39 | 19,3 | 2 | 26,53 | 26,3 | 2 | 18,36 | 18,1 |
| 3 | 6,12 | 6,1 | 3 | 21,43 | 20,5 | 3 | 16,32 | 16,4 | 3 | 19,39 | 19,5 | 3 | 26,53 | 26,1 | 3 | 18,36 | 18,3 |
| 4 | 6,12 | 6,3 | 4 | 21,43 | 20,4 | 4 | 16,32 | 16,2 | 4 | 19,39 | 19,5 | 4 | 26,53 | 26,1 | 4 | 18,36 | 18,4 |
| 5 | 6,12 | 6,2 | 5 | 21,43 | 20,5 | 5 | 16,32 | 16,3 | 5 | 19,39 | 19,4 | 5 | 26,53 | 26 | 5 | 18,36 | 18,3 |
| 6 | 6,12 | 6,1 | 6 | 21,43 | 20,4 | 6 | 16,32 | 16,4 | 6 | 19,39 | 19,3 | 6 | 26,53 | 26,6 | 6 | 18,36 | 18,4 |
| 7 | 6,12 | 6,2 | 7 | 21,43 | 20,5 | 7 | 16,32 | 16,3 | 7 | 19,39 | 19,3 | 7 | 26,53 | 26,5 | 7 | 18,36 | 18,4 |
| 8 | 6,12 | 6,2 | 8 | 21,43 | 20,5 | 8 | 16,32 | 16,3 | 8 | 19,39 | 19,4 | 8 | 26,53 | 26 | 8 | 18,36 | 18,3 |
| 9 | 6,12 | 6,3 | 9 | 21,43 | 20,4 | 9 | 16,32 | 16,2 | 9 | 19,39 | 19,4 | 9 | 26,53 | 26,6 | 9 | 18,36 | 18,4 |
| 10 | 6,12 | 6,1 | 10 | 21,43 | 20,4 | 10 | 16,32 | 16,4 | 10 | 19,39 | 19,3 | 10 | 26,53 | 26,4 | 10 | 18,36 | 18,4 |
Examination of the results:
The balance measures mass.
The body, whose mass m1 is to be determined is placed in the left-hand pan and standard masses (usually called weights) m2, are added to the right-hand pan to obtain equilibrium.
Graph Matching | To the top |
We are Andreea Ivan and Mihaela Ciucescu (15 years old). Our experiment is called "Graph Matching".
Objectives:
Analyze the motion of a student walking across the room, predict, sketch, and test position and velocity vs. time kinematics graphs.
Materials:
Vernier Motion Detector, computer, meter stick, masking tape
Procedure:
We placed the Motion Detector so that it points toward an open space at least 4 m long. We used short strips of masking tape on the floor to mark the 1 m, 2 m, 3 m positions from the Motion Detector. Using LoggerLite program, a student walk away from the detector with constant velocity and another click on “Collect” button.
The program sketch in the same time graphs d=f(t), v=f(t) si a=f(t). You can open the experiment file “01 Graph Matching.” Some position and velocity vs. time graphs will appear.
You can describe how you would walk to produce this target graph, and then test your prediction.
Simple Harmonic Motion | To the top |
Objectives:
measure the position and velocity as a function of time for an oscillating mass and spring system, determine the amplitude, period, and the frequency of the observed simple harmonic motion using the Vernier Motion Detector
Materials:
spring, computer, Vernier Motion Detector, rods, ring stand, clamps
Procedure:
I set up this experiment with my students from 9th R2 and 11th R2 grades.
First we established A=2cm and we collected data for a mass of m=150g, 200g si 250g hanged from a spring. After 10 s, data collection will stop. The position graph should show a clean sinusoidal curve. If it has flat regions or spikes, reposition the Motion Detector and try again. Using the position graph, we measured the period, T, of the motion and we calculated the frequency, f ( f = 1/T).
Camera Robot | To the top |
Hello, my name is Grosu George, I am 18 years old.
I would like to show you my first attempt at animatronics.
My robot is called Spyke 001 and it can rotate a camera placed on-top via remote control.
It’s made from old R/C car parts and a camera. Its basic function is to rotate the camera placed on-top using o remote control, just like the adaptive headlights you see in top of the end cars. But that’s not all that it can do, it has great mobility and control.
It’s very easy to make yourself, all the parts can be bought from any toy store and hardware store. The basic components are:
- one R/C car
- one digital camera or a spy cam (if you want it to look more like a spy gadget)
- a cowling to protect the electrics
- one extra motor to spin the camera
With this robot I won the first prize in the third edition of Grigore Moisil High School Science Fair, Bucharest, 13th October 2007.
So this is, in general, my robot I hope you liked it and are inspired to build your own.
