Question

Is angular momentum a scalar or vector? If it is a vector, what rule is used to determine its direction?

Answer 1

Scalar and vector quantity

1. A scalar quantity is one that has no direction but only has magnitude. The numerical value of some physical quantities can be used to describe them.
2. Mass, speed, distance, volume, and other concepts are examples.
3. A vector quantity is a physical quantity that has both direction and magnitude.
4. Force, acceleration, momentum, angular velocity, and so on are examples.

Angular momentum

1. In rotatory motion, angular momentum is a substitute for linear momentum.
2. In Newtonian mechanics, linear momentum, translational momentum, or simply momentum is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction
3. Angular momentum is the property of any rotating object given by moment of inertia times angular velocity.
4. Angular momentum is a vector quantity because it is equivalent to linear momentum (i.e. dependent upon both direction and magnitude). Because of this quality, it is vital to understand not only the magnitude but also the direction of angular momentum.
5. The Right-hand thumb rule is used to calculate the direction of angular momentum of a spinning or rotating body.

Right-hand thumb rule

1. To determine the direction of angular momentum, use the right-hand thumb rule.
2. According to the rule, if we open our palm and point all of our fingers towards the axis of rotation or the radius of rotation, then fold our fingers in the direction of rotation of the object, the direction in which the thumb points in the direction of angular momentum of that object.

Hence, angular momentum is a vector quantity. Its direction is determined by the right-hand thumb rule.