Reverse Pendulum
The law of momentum conservation in practice
Swing a pendulum that will set in motion the truck on wheels with low friction. Move the truck on the track and watch how its movement changes when you stop the pendulum using a magnet. In a sense we may consider this set of bodies to be isolated and each such set respects the principle of conservation of momentum. By application of this principle, each change of speed during the oscillating motion of the pendulum leads to a change in the speed of the truck. It also applies that a change in the speed of the truck will produce a change in the speed of the oscillating motion of the pendulum. The resulting motion of our set is always irregular.
