How to Calculate Angular Momentum
- 1). Determine the radius of the object's orbit around a fixed point. Measure this distance in meters in order to eliminate any frustrating conversions later.
- 2). Measure the angular velocity of the object in motion. Measure the number of rotations it makes in one second. If it is spinning too quickly, you can measure the number of rotations it makes in 10 seconds and divide it by 10 to get the angular velocity.
- 3). Determine the object's moment of inertia. This will depend on the shape of the object. A hollow spinning sphere, such as a basketball, has a moment of inertia defined as 2/3 MR^2 where M is the sphere's mass and R is the sphere's radius. A solid sphere has a moment of inertia equal to 2/5 MR^2.
- 4). Multiply the object's angular velocity by its moment of inertia. This will yield the object's angular momentum, measured in kilogram meters^2 seconds^-1, or Newton meter seconds. For example, a basketball with a radius of 0.12 m and a weight of 1 kg spinning at an angular velocity of 5 revolutions per second has an angular momentum equal to (5)(2/3)(1)(0.12)^2 = 0.048 kg*m^2*s^-1.
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