Ball in the air

The air stream doesn't allow the ping-pong ball to fall.


http://www.youtube.com/watch?v=mExwPCvNRJ0

Explosion in the box

We prepared:

• a stand
• 2 empty plastic boxes; smaller and bigger so that one could be a kind of lid to the other
• a small piece ( ball) of calcium carbid ( not wet or old)
• water in the wash bottle
• matches

We made a little hole in the bottom of the bigger box. Then a piece of carbide was put in the box in such way so that the hole was higher ang water could be added on the carbide ball.
Carbide reacts with water and in the reaction we obtain a gas - acetylene C2H2:

CaC2 + 2 H2O = C2H2 + Ca(OH)2

Acetylene is flammable and it burns silently if it's pure. When it is mixed with air , explodes and throws away the upper box.



http://www.youtube.com/watch?v=A9QvpGiNgQw

Fire without matches

We carried out the experiment wich shows how to make a fire without matches.

We used potassium permanganate KMnO4 and glycerine C3H5(OH)3.

Be careful and wait while doing it, fire appears after several seconds.

http://www.youtube.com/watch?v=kpae8Xh90mI

Another balance with two forks a toothpick and fire

To make our experiment we need a pair of forks, a toothpick, a glass and a match.

First, we have to intertwine the forks with the toothpick and leave them in balance at the edge of the glass. The balance is obtained because the centre of the gravity is under the support point.

What would happen if we burnt the edge of the toothpick that is inside the glass?

A part of the toothpick is burnt, but the flame is put out when it’s at the edge of the glass and the balance of the forks is kept.

The loss of volume of the toothpick that is burnt, doesn’t affect to the centre of the gravity

by Teresa and Ángela

An eddy in a bottle

To make our experiment we need two plastic bottles of one and a half litres.

First, drill a hole in the two bottles corks.
Then, fill one of the bottles with water to about three quarters and join the two plugs per cylinder.
To unite the two bottles it can be used a tape.

It is very important the union between the bottles.

When the water on the bottles is empty is upper, it seems that the water does not fall easily to the bottle bottom, but if we give a circular motion to the bottle top and creates a swirling, water falls easily.

By placing the bottles on top, water doesn’t fall to the bottom because of the compressed air trapped in the bottle which is down. It can pass through it, as there is no room for it.

When the eddy is generated by moving the top bottle, it is communicated the air in both bottles and the water in the top bottle falls easily into the bottom bottle.

by Yulia

Drawing with sand

To make our experiment we needs a plastic bottle, sand beach and a rope.

First we have to construct a pendulum with the bottle.
Them we cut the base and make a couple of holes in one of the sides in order to pass the rope and another hole in the stopper to exit the sand filled.

If the bottle is away from the position of equilibrium it begins to oscillate, describing a trajectory that will be recorded in the soil by the stroke that left the sand that falls from the bottle.

Depending of the length of the rope and on the relationship between distances, we can get different figures.

The figures obtained are known as Lissajous figures, names after French scientist Jules Antoine Lissajous, who first observed this in 1857.

by Anabel and Teresa

The underwater drop

Materials:

1. A small container and a big glass.
2. Oil
3. Water
4. Alcohol
5. Glue and coin.
6. A spoon.

If the container is made of plastic, we stick a coin at its base in order to get more stability and avoid floating.

We fill the half a container with oil.
We put it at the bottom of the glass.
We pour the alcohol necessary to cover the container very carefully.

Then, we add water little by little with a spoon (it must slip from the wall of the glass).
Small container's surface filled with oil will adopt a convex shape until the water you add is enough. Then, the oil will separate from this container and it will have a spherical form that will remain just in the middle inside the oil and water mixture.

EXPLANATION:
First, we must know the densities of the liquids we use in the experiment.
- water (1g/ml)
- oil (0'92 g/ml)
- Alcohol (0'75 g/ml)

The oil floats in the water because it's less dense than water, but it sinks into alcohol because it's denser than it. In conclusion, you can prepare a mixture with alcohol and water because inside it, oil won’t float or sink.

by Ana, Marta and Belén

Union doesn’t make strength

The materials we need to do the experiments are a balloon and drawing pins.

First you have to push the balloon against twenty drawing pins and make sure they don't explode. The strength exerted has distributed on all the drawing pins so there isn’t sufficient pressure to explode the balloon.

The effect of strength doesn't depend only on its intensity, but also on the surface on which exerts. If the surface is very large, the effect of the strength will be spread over it all.

Next, push the balloon against one drawing pin and notice if it explodes. In this case, all the strength mass and pressure at a very specific point makes the drawing pins go through the balloon and explode.If on the contrary, the surface is small, the intensity of the strength mass over it is stronger and its distorted effect increases.

by Lourdes and Blanca

Does smoke rise or goes down?

To realize our experiment we need a bottle of plastic, a sheet of paper and a few matches.

First we do a couple of holes in the bottle of plastic, one in the top part and another one near the base of the bottle.
Then we take the sheet paper and cut away a rectangle of 10x15 cm.
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 there 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 does not 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 are 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 (currents of convection).

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 do not take place (there are not produced rising currents of convection) and the smoke (denser than the air) it rushes to the bottom of the bottle.

by Francisco and Fernando