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

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

OIL POMP

Materials:
1 One small container and one larger glass
2 Oil
3 Water
4 Glue and one coin
5 Spoon
6 Alcohol

Assembly:
1. If the container is of plastic we put on the base one coin to give it stability and to avoid that it floats.
2. You take the small container, and you fill the container until the middle with oil and you see that the oil sets on the bottom of the glass.
3 Inside the glass you fill with precaution, the amount of alcohol that you need to cover the small container. Then with a spoon, you add, little by little, water.The surface of the oil from the small container will be more and more convex, when the water that you have added is the necessary, the oil will give off the container and will forma sphere that will be floating inside the mixture of water and alcohol.

Explanation:
The densities of the three liquids : water (1g/ml), oil (0,92g/ml) and alcohol (0,79g/ml).
The oil floats on the water because it is less dense than the water, but the oil doesn’t float on the alcohol because it is denser. So you can prepare one mixture of water an alcohol, where this oil won’t float and won’t sink until the bottom.

by Macarena, Irene and Sofía

A whirlpool in a bottle

Materials:


Two bottles made of plastic 1,5 l.
Insulating tape

Execution:

First, we make a 1 cm hole at the tops of the bottles. Then, we fill one of the bottles with 75% of water and join the bottles by means of the tops. To join the two bottles we use the insulating tape. This joint is very important, so do not be stingy with the insulating tape.


When the bottles with water is on top of the other, the water does not fall easily to the empty bottle, but if we make a circular movement with the upper bottles, it generates a whirlpool, and the water falls easily.

Explanation:

When we place the bottles full of water on the top, the water does not fall because of the low compressibility of the air, which takes up the lower bottle and does not let any space for the water to fall.
By the time, the whirlpool is generated by the air of the two bottles that passes from one to the other and the water of the upper bottle falls easily.

By Mercedes and Fátima

An eddy in a bottle

In order to make our experiment we needed two plastic bottles of 1´5 liters.

In the first place, we perforated a hole of 1 cm in the corks of the two bottles. Soon we filled one of the bottles with water until approximately three fourth parts and if united the two bottles by the corks. In order to unite the two bottles insulating tape can be used. Is very important a good union between the bottle.

When the bottle with water is on the empty bottle it is observed that the water does not fall easily to the inferior bottle, but if we give a circular movement to the superior bottle is generated an eddy and the water falls easily.

When placing the bottle in the superior part, water does not fall by the little compressibility of the air locked up in the inferior bottle that does not leave space to the water that falls. When the eddy is generated when moving the superior bottle, it is put in communication the air that is in both bottles and the water of the superior bottle falls easily in to the inferior bottle.

Colegio Sagrado Corazón (Esclavas)
Sevilla (Spain)