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

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