A handful of small ball bearings or polystyrene balls represent particles in this demonstration. The vibration provided by the vibrating plate represents changes in temperature while the polystyrene ‘plug’ and masses represent applied pressure.
When the ‘temperature’ is low (the vibration is low) the particles are not seen to move much, this reflects the energy level of the particles. As the 'temperature' (vibration) increases, the particles move more and more erratically, eventually bouncing up to the top of the tube. This represents how gas molecules act when high temperatures are applied.
Add the bung and some small masses and the level of bouncing will drop and the ‘particles’ appear more concentrated. This shows that when you pressurise the gas at a specific temperature, the particles become tighter packed and therefore have less kinetic energy.
Many science departments have old units from the 60s or 70s which will still perform well, though routinely oiling the motor parts will keep things running smoothly.
Here’s the technical bit…
The temperature of a gas is the measure of its mean kinetic energy – the molecules are in constant motion and energy is associated with that motion. The higher the temperature, the greater the motion. The density of a gas is the sum of the mass of the molecules divided by the volume or space which the gas occupies Pressure of a gas is a measure of the momentum of the molecules – The molecules impart momentum to the walls of the container producing a force that can be measured accurately.