Question

Take a hard boiled egg or tippee top and put it lying down on a table and start to spin it, if you spin it fast enough it will start to spin in an upright position. How do the egg, and tippee top remain stable in their rotating positions? What other toys can you think of are based on interesting quirks of physics? (Try to explain the physics behind them!)

Answer 1

The every spinning toy, be it a top, an egg or something else, is based on the single law of physics. Which is The conservation of angular momentum.

This law is based on the fact that an spinning object will keep spinning until a torques is applied on it to change its momentum.

here L is the angular momentum and is the torque applied.

For example, consider a bicycle. When a bicycle is going in straight line, it will keep going without any disturbance untill the speed of wheels is maintained against the internal frictions. Now if you tilt the bicycle a bit( means if you apply a torque on the wheels), the direction of the cycle( that is the angular momentum of the wheels which is a vector quantity) changes. Which results in turning the bicycle. If you try to rotate the handle of cycle without tilting it, that is going to be a disaster, just because of the angular momentum conservation.

You can name many other toys, for example a swing is based on the principle of forced harmonic motion and resonance.