Can anyone tell me something about Angular Momentum?

Answer 1

Angular momentum is a vector quantity. It is analogous to linear momentum but it is a rotational motion. Both are subject to the same Newtonian laws.

Think of it as a spinning object. Angular momentum of an object around a reference point will continue to rotate about that point unless acted upon by an external torque. It is a conserved quantity, meaning that it stays constant unless acted upon by an external torque.

It may be defined as the inertia of an object or system of objects in motion about an axis that may or may not pass through the object. It is affected by the mass, velocity, and distance from the axis point.

It is used in such calculations as to conclude that a planet must have a moon because it is rotating slower than expected, or the increase spin of stars that have compacted from a larger star (black hole, neutron star, white dwarf), or to measure precession.

In Theoretical Physics, angular momentum may be described using Noether's theorem. It is quantized in Quantum Mechanics in that it is said not to vary continuously but only in quantum leaps. Since most subatomic particles have a permanent built-in angular momentum which is not due to their motion through space.

Answer 2

All of the above answers are essentially correct. But one aspect of angular momentum that hasn't been mentioned is the effect of the conservation of angular momentum.

Because angular momentum is a vector quantity (it has not only scale, but direction), attempts to change the angular momentum of a system (by applying a torque to a rotating body) result in a torque in a different direction to maintain constant angular momentum. This is the principle behind a gyroscope (and a bicycle wheel). As the gyroscope spins about its vertical (yaw) axis, an attempt to torque the gyro around its roll axis (i.e. side to side) will result in a net torque about the pitch about the pitch axis (i.e. fore/aft). Since ships with long keels are much more stable in the fore/aft direction (they are supported by much more water in those directions), the gyro can stabilize the ship against roll motion imposed by cross waves.

Answer 3

If you spin a top, or a dreidel, it continues to spin because of the angular momentum that you have imparted to it. Friction takes over, and eventually the device will stop. The earth's rotation represents a huge quantity of angular momentum, and the only source of friction is the ocean tides, so the earth doesn't slow its rotation very much.

Answer 4

The total angular momentum of the entire universe is zero. This means the universe is isotropic (has no preferred direction).