Saturday, 20 June 2009

Good bye friends

Une monnaie capricieuse

Le matérial dont nous avons besoin pour réaliser l'expérience est:

Un verre
Une monnaie
Une carte d'un jeu de cartes

Préparation

Mets la carte sur le verre et la monnaie au centre de la carte.
Fixe le verre avec une main et tire la carte avec l'autre main avec énergie.
Le monnaie tombe dans le verre.

Qu'est-ce qui s´est passé?

La résistance d´un corps à changer son état de repos ou de mouvement s´appelle inertie.
Après avoir tiré la carte, la force de frottement entre la carte et la monnaie tend à deplacer la monnaie sur la carte. Si nous le faisons avec énergie, la force de frottement ne réussit pas à surpasser l´inertie de la monnaie qui tombe dans le verre. Mais si nous tirons lentement de la carte, la monnaie se déplace sur la carte.

Vous avez compris?





Begoña et Julia

La chaleur de nos mains

Le matériel dont nous avons besoin c´est:

Un pot de verre avec un couvercle
Une paille de rafraîchissement
Colle
Alcool

Nous pouvous faire un trou sur le couvercle avec un marteau et un clou.

Nous mettons la paille dans le trou et nous remplissons d´alcool le pot (plus ou moins deux centimètres). Et nous plaçons le couvercle.

Nous couvrons le pot avec nos mains et nous voyons que l´alcool monte par la paille.

Explication

La température de notre corps est supérieure à la température de l´air dans le pot
Pour entourer le pot avec nos mains fournissons de l´énergie au pot et comme ça augmente la température de l´air dans le pot. Cela produit l´augmentation de la pression aussi qui pousse le liquide que monte par la paille.

Si nous levons le convercle du pot, la pression dans l´interieur récupére sa valeur originale et le liquide qui monte par la paille tombe dans le pot.




Alicia, Marta et Jiamei

Thursday, 18 June 2009

Skydiver



A nice work done by 12th year physics' students Nuno Oliveira and Filipa Martins about skydiving and terminal speed.

Sunday, 14 June 2009

Rainbow Milk

Group 5 - Elena B, Cynthia C, Karina L, Laura P - Colegiul Naţional "Mihai Eminescu" Satu Mare, România


Red, blue and yellow are called the primary colors. Just by mixing these colors, you can get all the colors of the rainbow:
RED + YELLOW = ORANGE; RED + BLUE = PURPLE; BLUE + YELLOW = GREEN

What you need: red, blue and yellow food color; 1 cup milk; dish soap; shallow bowl

Directions:

  • Pour 1 cup of milk into the bowl
  • Add 3 drops of red food color to one edge of the bowl
- 1/3 of the way away, add 3 drops of blue food color
- 1/3 of the way away add 3 drops of yellow
- don't mix or jiggle the bowl
  • Squeeze a drop of dish soap in the center of the bowl
  • Record what you see.
  • What do you think happened?

Saturday, 13 June 2009

"Shaving foam"

Decomposition of H2O2 :

To carry that experiment you need:

  • high buret
  • 30% hydrogen peroxide (perhydrol)
  • solid potassium or sodium iodide ( KI or NaI)
  • soap powder
BE CAREFUL! 30% HYDROGEN PEROXIDE IS VERY CORROSIVE!

Pour perhydrol into the buret (about 1/5 of its height), then pour the soap powder -
about 1 teaspoonful. Mix the soap with the liquid.

After that add 1/2 of teaspoonful of solid potassium iodide. Be carefull because foam appears very quickly and it could make some brown stain - it contains iodine I2 .

3H2O2 + KI = 3H2O + KIO + O2

2KIO + H2O2 = I2 + 2KOH + O
2


Oxygen causes a lot of foam if soap is mixed with perhydrol before adding KI.


http://www.youtube.com/watch?v=OKUgIKPPwhE

Friday, 12 June 2009

Concave Mirrors



A movie of experiments using one and two concave mirrors.

Bernoulli principle with balloons



A movie about Bernoulli's principle applied to a stream of air passing between two balloons.

The balloon that doesn't explode



A balloon full of water can be burned for a long while by a burner without exploding.

Barbeque balloon



This is an experiment where we can see that vegetable oil may create a membrane that prevents a balloon from exploding.

Potassium and water


This video is about the reaction of potassium and water.

Tuesday, 9 June 2009

Air versus Water 2



An experiment that shows that at small depths atmospheric pressure is bigger than water pressure.

Effusive Volcano


An experiment with balsamic vinegar and baking powder to produce an effusive volcano.

Plasma Ball



This is an experiment about plasma. In physics and chemistry, plasma is a partially ionized gas, in which a certain proportion of electrons are free rather than being bound to an atom or molecule. The ability of the positive and negative charges to move somewhat independently makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Plasma therefore has properties quite unlike those of solids, liquids or gases and is considered to be a distinct state of matter.

Layered Liquids

Group 5 - Elena B, Cynthia C, Karina L, Laura P - Colegiul Naţional "Mihai Eminescu" Satu Mare, RomâniaLP_Layered_liquids2.gif
Have you ever heard the phrase "oil and water don’t mix"? First we will test that expression, then look at interesting combination of several other liquids.

Oil and WaterLP_layered_liquids.jpg

You will need the following materials:

• ¼ cup (60 ml) water
• ¼ cup (60 ml) vegetable oil
• a small glass
• food coloring

First pour the water into the glass. Add a couple of drops of food coloring and mix. Next add the oil. What do you see? Which layer is on top?

Tightly cover the glass with plastic wrap or your hand (if it's big enough). While holding the glass over a sink (in case you spill), shake the glass so that the two liquids are thoroughly mixed. Set the glass down and watch what happens. Do oil and water mix?

The word “miscibility” describes how well two substances mix. Oil and water are said to be “immiscible,” because they do not mix. The oil layer is on top of the water because of the difference in density of the two liquids. The density of a substance is the ratio of its mass (weight) to its volume. The oil is less dense than the water and so is on top.

The next experiment examines the miscibility and density of several liquids.

You will need the following materials:

• ¼ cup (60 ml) dark corn syrup or honey
• ¼ cup (60 ml) dishwashing liquid
• ¼ cup (60 ml) water
• ¼ cup (60 ml) vegetable oil
• ¼ cup (60 ml) rubbing alcohol
• a tall 12 ounce (350 ml) glass or clear plastic cup
• two other cups for mixing
• food coloring

Take the 12 ounce glass. Being careful not get syrup on the side of the glass; pour the syrup into the middle of the glass. Pour enough syrup in to fill the glass 1/6 of the way.

After you have added the syrup or honey, tip the glass slightly and pour an equal amount of the dishwashing liquid slowly down the side of the glass. Does the dishwasher liquid float on top of the syrup or sink to the bottom?

Next mix a few drops of food coloring with water in one of the mixing cups. Color the rubbing alcohol a different color in another mixing cup.

Be careful to add the next liquids VERY SLOWLY. They are less viscous (i.e., not as thick) and mix more easily than the previous liquids. We don't want them to mix. Tip the glass slightly, and pouring slowly down the side of the glass, add first the colored water, then the vegetable oil, and finally the colored rubbing alcohol.

On a piece of paper, make a sketch of the glass and its liquids, labeling the position of each liquid in your glass.

Why do the liquids stay separated? Can you think of several ways that the liquids in the glass are different? Try to describe some properties that differ in each of the liquids in the glass.

One property that is different in all of the liquids is color. Another property unique to each liquid is thickness (viscosity).

The property of the liquids that is responsible for the layering effect is density. Can you guess what the relationship is between the density of a liquid and its position in the glass?

Another property that keeps the liquids separate is that some of them are immiscible liquids, in other words they do not mix with each other. As you proved in the first experiment, oil and water are immiscible liquids. On the other hand, water and rubbing alcohol are miscible and will mix with each other. Water and the dishwasher liquid will also mix.

Stir up the liquids in the glass and watch what happens to the layers. Have any of the layers mixed (are they miscible in each other)? Wait a few minutes and look again. Have any of the other liquids separated?

Alternate procedure: Rainbow in a glass.

You will need the following materials:

• four different colors of food coloring (e.g. red, yellow, green, blue)
• five tall glasses or clear plastic cups
• ¾ cup (180 g) of granulated sugar
• a tablespoon for measuring
• 1 cup (240 ml) water

In the first glass, add one tablespoon (15 g) of sugar. In the second glass, add two tablespoons of sugar, three in the third glass, and four in the last glass. Then add three tablespoons (45 ml) of water to each glass, and stir until the sugar is dissolved. If the sugar in any of the glasses will not dissolve, add one more tablespoon (15 ml) of water to all of the glasses, and stir again. When the sugar is completely dissolved, add two or three drops of red food coloring to the first glass, yellow to the second, green to the third, and blue to the last glass.

In the remaining glass we will create our rainbow. Fill the glass about a fourth of the way with the blue sugar solution. Next, carefully add the green solution to the glass. Do this by putting a spoon in the glass, just above the level of the blue solution. Slowly pour the green solution into the spoon, raising the spoon to keep it just above the level of the liquid, until the glass is half full. Add the yellow solution, and then the red one in the same manner. What do you notice about the colored solutions?

The amount of sugar dissolved in a liquid affects its density. The blue solution has the most sugar dissolved in it and is therefore the densest. The other solutions are less dense than the blue solution, so they float on top of it. The densities of the solutions should be very close however, and the solutions are miscible, so you will see that the layers do not form well defined boundaries as in the first experiment. If done carefully enough, the colors should stay relatively separate from each other. What do you think will happen if you stir up the liquids in the glass?

The Fire Extinguisher

By David Arez
Escola Secundária de Loulé Portugal




This is movie about the functioning of carbon dioxide fire extinguishers.
If oxygen is removed by a gas that isn't combustive then the combustion reaction comes to an end.

Diffusion

Group 3 - Alexandru S, Darius O, Raluca B, Vlad M - Colegiul Naţional "Mihai Eminescu" Satu Mare, România


Air versus Water



A movie that gives a good idea of atmospheric pressure. Our atmosphere is capable of keeping a papel up even against a glass full of water. In fact, one would need a column of water with a height of about 10 meters in order to have equal water and air pressures.

Does smoke rise or goes down?

To make our experiment we need a bottle of plastic of 1´5 litres, a sheet of paper and a few matches.

First we make a couple of holes in the bottle of plastic, one in the top part and another one near the base of the bottle.

Them we take the sheet paper and cut away a rectangle of 10x15 cm (10 times fifteen). We coil the paper to obtain a small cylinder of approximately 15 cm of length. Finally the small tube of paper interferes for the top hole of the bottle.

On having ignited the small tube of paper with a match a small flame is formed and is observed that for another end of the bead goes out a column of very dense smoke that falls down inside the bottle. In the exterior scarcely there is smoke.

If we cover the low hole with a finger, the small tube of paper goes out and smoke doesn’t go out.

Explanation:

On having burned the small tube it departs from the paper it is clear in the shape of particles that, together with the gases that formed in the combustion and the air they form the smoke.

In normal circumstances, the smoke ascends dragged by the warm air of the combustion.

In our experiment, the smoke that takes place is produced in the interior part of the small tube travels along it. Inside the bottle, there is no warm air, so that, when the smoke goes out for the low end of the small tube there aren’t produced rising currents of convection and the smoke, denser that the air, it rushes to the bottom of the bottle.



by Clara, Beatriz and Inés

Sunday, 7 June 2009

Spaghetti tightrope walker

Material: one spaghetti


1 Stand the spaghetti placed about your two hands.
2 It moves slowly one of the hands towards the other one without inclining the spaghetti.
3 Regardless of the hand that moves the two end up together in the center of the spaghetti that will remain in balance without falling.

Explanation:

By moving the hands, spaghetti slides without falling, keeping the gravity center between the fingers.





by Antonio and Antonio

Saturday, 6 June 2009

A bottle with a hole

In order to make our experiment, we only need a bottle of water with it’s cap.

We make a small hole in a plastic bottle, about a half of its height, and we fill it full of water, while we are covering the hole.

If we remove our finger from the hole, no water comes out, but if we remove the cap of the bottle, the water starts to come out. But why?

If the cap is put, the internal pressure on the hole is equal to the external pressure and that’s why the water doesn’t come out of the hole.

But, if we remove the cap, we allow that the air comes into the top of the bottles, breaking the previous balance. The internal pressure on the hole is greater than the external pressure, so the water comes out of the bottle.






by Irene and Rafael

Thursday, 4 June 2009

Fakir baloon



This is an experiment where we can see that if the same force is distributed over a bigger surface then pressure is smaller. Since what makes the balloon explode is pressure, the more "punaises" lesser will be the pressure exerted on the balloon. With only one "punaise" the balloon will explode.