Session 2: Pressure /solid-liquid-gas

Objective 1 : Demonstrate that the pressure in the phase solid or fluid (liquid or gas) is different

Explanation

Pressure is the result of a force applied on a given surface; because of their nature the surface of contact of the fluid (liquid or gas) will be different from that of the solid.

The results will be that the force that has to be considered in a fluid will not be the same for fluid than for liquid. Indeed if you put all the see in a reservoir and then you put your hand under the reservoir, the pressure on your hand is due to all the weight of the sea water. While if you put your hand in the sea water at a depth of 2m the pressure is that of the column of water above your hand. Let’s experiments this.

Material

• Plastic bags in light plastic without holes!
• Small and bigger plastic containers as light as possible (ice cream box)
• Towels
• Floor Cloth

Maximum duration

30 Minutes

Main question to be asked

What is the difference between the pressure between a solid and a liquid or a gas?

Main activities

1. Put plastic containers in front of the group of students and ask them to put a plastic bag around one hand
2. Ask them to dip their hands in the water container
3. Ask them to express their feeling about this experiment. How does the water act on their hand?
4. Then suggest that they plunge their hand (without plastic bags) into the bottom of the container. Repeat this experiment taking first the small container with just a little bit of water and then with as much water as possible. Do they feel a difference?
5. Repeat this experiment, with the same two levels of water you dip one hand at the bottom of the container. Is there a difference between small and big containers?
6. Now take the small and the big containers with the highest level of water and put them carefully on the top of your hand which is out of the water on the table!

Note that the container should be light so that its weight is negligible compared to the weight of the water.

This experiment is a step between experiments of the pressure of solid and fluid. At this stage ask your students to express themselves and to react to these experiments.This can be done by drawing, writing or speaking.

Conclusion/Plenary

During these experiments students should have felt pressure within a liquid and they have experimented that there is a difference between a pressure within a fluid and with the contact of a solid.

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