Session 4: Pressure and Height

Session 4: Pressure and Height – Experiment 2

Objectives 1: With this experiments students will observe that the pressure varies with the height of liquid, making the experiments from inside the liquid.

Explanation

Material

Transparent container
Glass of water
Small floating object
Soda plastic bottles with three different diameter
Or Plexiglas tubes with 3 different diameters
Take a piece of rigid material, that resist to water, light plastic for example

Maximum duration

45 minutes

Main question to be asked

Introduction/Starters

Do a simple experiment in front of the children:
Choose a transparent container full of water.
Put the small floating object on the water surface.
Then put a glass of water upside down and push it very horizontally, very straight, slowly into the water.
Before starting to push, ask your students what they are expecting to see.
After the experiment, discuss with them why the glass is not full of water?

You can also propose them to do the experiments themselves.

Main activities

If you want to make a qualitative experiment, you can choose 3 rigid Plexiglas tubes with diameter of 2,5 and 10 cm

If your students are younger and the experiments is more qualitative, used aplastic bottles with volume 0,33l, 1,5 and 2,0 litres, from several sizes and cut the top and bottom to obtain cylinders of different sizes.

A. Test the parameter height of liquid

Close the bottom of the middle size tube with a piece of light rigid plastic.
Push the piece of plastic firmly and then dip the tube within your container of water at the half of the height. If you did well the pressure should ensure the seal and the water does not enter the Plexiglas tube
Question to ask your students: how much water will you need to add before the piece of plastic will be released?
Do the same experiments, and stop filling with the water just before releasing the piece of plastic. Then push your tube lower within the water. What do you have to do to release the plastic?
Conclude with the students, as the height of water increases, the pressure…

B.Test the parameter of diameter of the tube

Perform exactly the same experiments as in 1) changing the diameter of the tube.

Refer to the experiments of session 1, if the pressure is the same both sides of the plastic, but the area has increased the force applied on the plastic should increase more water.