The law of conservation of energy states that energy cannot be lost or gained but just converted from one form to another. For example, when a pendulum is elevated to a certain height it acquires a potential energy. When the pendulum is released that potential energy is converted to kinetic energy in the downswing and back into potential energy in the upswing. However, unless a source of energy is introduced into the system such as, for example, giving the pendulum a push, the pendulum will not reach a higher elevation than the one from which it was originally released. In the video below, uploaded into You Tube by Johnny Rico, Professor Walter Lewin from the Massachusetts Institute of Technology (MIT) puts his life on the line to illustrate this principle.
Newton’s Cradle is a device that is used in teaching to demonstrate the physical laws of conservation of energy and momentum. The device consists on a series of spheres suspended from wires. The spheres are pulled and released, and then collide with each other. But there must be something charming about Newton’s Cradle which has made it transcend the classroom, as it is used is also used for entertainment, or as a decorative toy, and has even been featured in movies. When the moving ball collides with the stationary balls, the force is transmitted through the stationary balls to the ball on the far side. Depending on the number of moving balls and stationary balls as well as their location and the timing of release of the balls, several recurring collision patterns can be generated as shown in the video below.
If you have the time, there is even a computer simulation of Newton’s Cradle that you can operate without having to deal with the effects of friction which eventually dampen the performance of the real device.