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.
The domino tumble is a great example of the conversion of potential energy into kinetic energy (energy of movement) and the internet is filled with videos of elaborate domino tumbles involving thousands of dominoes such as the one below.
Less well known variants of the domino tumble are the double domino and domino amplification effects.
The double domino effect occurs when the regular forward wave of toppling dominoes is followed by a second wave in the opposite direction. This occurs because the first wave leaves the dominoes lying partly on top of each other with some of their potential energy still intact. When the terminal domino falls to the ground, it fails to provide the support needed for the domino immediately before it which falls to the ground too followed by the next one and so on. The process and the math involved are explained in the video below by Matt Parker from standupmaths.
The domino amplification effect is a far more interesting for me because with a tiny input energy you can release a huge amount of energy in a process that is somewhat similar to a chain reaction. This is possible because a domino can topple over another domino that is 1.5 times larger. Thus by placing dominoes of increasing size one after the other you can topple a gigantic domino using a much smaller one achieving amplifications factors in the billions. The process and the physics involved are explained in the video below.
The domino amplification effect was featured in an episode of Mythbusters shown in the video below.