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Newton's Cradle

Infinity candle

Newton's cradle is a classic physics gadget that demonstrates the law of conservation of energy and momentum...

Newton's cradle is probably one of the most famous physics gadgets, that demonstrates the law of conservation of mechanical energy and momentum. It usually consists of seven steel balls that almost touch each other and are suspended from a frame by thin cables. The base of Newton's cradle in the picture is made of marble, which adds stability, and gives it a beautiful appearance.

By lifting the sphere up, we do some work and as a result, the sphere gains more potential energy because it is now higher than the other spheres. By releasing the sphere, it starts to move and its potential energy begins to convert into kinetic energy. The moment before it collides with the next ball, its potential energy has been converted into kinetic energy and it has reached a certain speed. On impact, it transfers its momentum (which is equal to the product of the sphere's mass and velocity) to the next sphere, which in turn to the next sphere in the row, and so on until the last sphere in the row swings up and the whole cycle repeats. Of course, you can release two or more spheres at the same time and explore how the law of conservation of momentum works in different cases.

Inevitably, at some point the oscillation stops because energy is constantly being lost, for example, to overcome frictional forces and to release heat and generate sound waves during collisions. But a good quality Newton's Cradle can swing for quite a long time before it stops, the cradle in the picture, for example, has a swinging time of up to 50 seconds.


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