Why does reducing volume increase pressure?
Practical Activity for 14-16
Apparatus and Materials
For each pair of students
- Kinetic model kit, two-dimensional
- Marbles, coloured, 20 - 24, about 1 cm diameter
- Metal tray lined with cork mat
Health & Safety and Technical Notes
Watch out for marbles which may roll accidentally onto the floor.
- Agitate the tray, listening to the sound of the marbles hitting the sides of the tray.
- Put a ruler across the tray to reduce the area occupied by the marbles. As it will not be easy to hold the ruler still, it helps to put a book in the tray and to hold the ruler firmly up against it.
- Now agitate the tray in the same way as earlier. You should hear an increase in noise as the marbles strike the tray walls at a greater rate than before.
- This model shows the increase in pressure caused by a decrease in volume.
- If students add a lot more marbles, they can listen to what happens to the pressure (it rises).
This experiment was safety-tested in March 2005