Astronomy Practice Exam

What describes angular momentum?

1. The force acting on an object in motion

2. Mass and speed of a stationary object

3. Rotational momentum of a spinning or orbiting object

4. The energy from a moving object

The correct answer is: Rotational momentum of a spinning or orbiting object

Angular momentum is defined as the rotational momentum of a spinning or orbiting object. It is a vector quantity that depends on both the object's velocity and its distance from the axis of rotation. For a spinning object, angular momentum can be calculated using the product of its moment of inertia and its angular velocity. In the context of celestial bodies, such as planets or stars, angular momentum plays a crucial role in governing their motion in orbits and how they behave as they rotate. This principle is fundamental in explaining various phenomena in astronomy, such as the stability of orbits and the dynamics of galaxies. The other choices do not accurately describe angular momentum. The force acting on an object in motion relates more to linear momentum and Newton's laws of motion. Describing mass and speed of a stationary object lacks relevance, as angular momentum specifically pertains to motion about an axis. The energy from a moving object typically describes kinetic energy rather than angular momentum, which is specifically about rotational motion. Thus, identifying angular momentum as the rotational momentum of a spinning or orbiting object highlights its role in both physics and astronomy.