TROLLEYS ON RAILS
mechanics
Description of the device
On the rails there are two trolleys opposite each other. When they collide, a transfer of energy occurs between them – this demonstrates the principles of conservation of energy and conservation of angular momentum.
Phenomenon
Despite the fact that only one person pulls on the rope, both trolleys come closer to each other. That’s the manifestation of the Newton’s third law of dynamics: when you act on the other trolley-person system with a force of given value, a force of the same value but opposite direction acts also on you. When the non-moving trolley is hit by the moving one, it takes over the moving trolley’s momentum and drives away, while the hitting trolley stops. It’s an example of elastic collision. If the trolleys got stuck with each other, a nonelastic collision would occur.
How to use it
Each of you should sit in a trolley when the trolleys are placed on opposite sides of the rails. One of you should grab the free end of the rope and try to pull the other trolley. Which of the trolleys is moving? Then get off the trolleys. Let an empty trolley stand in the middle of the rails. Push the other trolley (also empty!) in its direction, so that it hits the trolley in the middle of the rails. What can you observe?
CAUTION!
DON’T STAND BETWEEN THE TROLLEYS – IT’S DANGEROUS! DON’T PUT YOUR LEGS BETWEEN THE TROLLEYS – IT’S DANGEROUS! PROCEED WITH EXTRA CAUTION.