In physics, angular momentum is a quantity that can be used to characterize the balance of rotational motion. When looking at an object rotating about its axis, there are two types of angular momentum involved:
- the rotation along (or perpendicular to) the axis and
- rotation around or parallel to the axis as well.
The first term in this equation is know as ‘momentum’, while the second term is called ‘torque’. This property of objects in circular motion was described by Issac Newton in his book “Principia Mathematica” when he stated “The vis insita, or innate force of matter…on revolving with an uniform velocity (as trochoids), tended perpetually to continue that motion in the same direction in which it was begun”. For this purpose, he introduced into mechanics three important laws, that can be remembered by the letters “I.A.”, representing respectively:
- The law of Inertia – It states that “…every body perseveres for ever in its state either of rest or uniform motion unless acted upon by some external force”
- The law of acceleration – “The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the straight line in which that force tends”. This means that “If a body A were struck by two forces F1 and F2, where F1 > F2, then, impressed on this body were a force 2F1 – F2”.
- The law of action and reaction – This states that “To every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal and directed to contrary parts”.
Every force acts through a distance. This means that a force applied for a certain time will produce an acceleration. According to classical formulations of mechanics, i.e., Newton’s theories of motion , the magnitude of this acceleration is proportional to the force and inversely proportional to the mass of the object. In addition, angular momentum has been shown as a product of both rotation rate and radius (See equation (1)). “The angular momentum L is defined by the product of the moment of momentum, p×L = m×r ×v”.
m – Mass of object
r – Radius of rotation/distance between two objects in orbit.
v – Velocity