Gravity and Angular Momentum: What, How and Detailed Explanations

This article discusses about gravity and angular momentum. Both of these terms have very deep concepts and cannot be discussed in detail in this article.

Although, we shall see the meaning of these terms and study about them in brief. In later sections we shall see the relationship between these two. These terms are very simple and we must be knowing their meanings but we shall study them from scratch. Let us start with the meaning of gravity.

What is gravity?

Gravity is a weak attractive force that acts between two objects by virtue of their masses. That means greater the mass between them greater will be the attractive force.

Gravity may seem very insignificant to us as we don’t get attracted towards each other due to our masses. But the effect of gravity always surrounds. It can be proved simply by jumping off a table or chair, we never go up. We always get attracted to the surface. This is due to the Earth’s gravitational pull on us.

What is angular momentum?

Angular momentum is simply a product of two quantities that is moment of inertia and angular momentum of the body.

It can be said that it is a measure of rotation of a body. The momentum can also give rise to force due to the inertial effect. This is the spin of an object, the velocity of an object spinning around its axis. The application of angular momentum is exploited by gyroscopes to stabilize the vehicles in which they are used.

gravity and angular momentum
Image: Gyroscope

Image credits: anonymous, GyroskopCC BY-SA 3.0

Does gravity affect angular momentum?

No, gravity and angular momentum are not related to each other. This is because the causes of both of them are different.

Angular momentum is caused due to the rotation of masses. Greater the mass and its rotational speed, greater will be the angular momentum. Incase of gravity, the velocity factor does not come in. The effect of gravity is independent of mass. Only the gravitational force depends on the masses of both the objects.

Why gravity has no effect on angular momentum?

As discussed in above sections, angular momentum depends on three things only that is mass, radius and velocity of the object.

Gravity only pulls other objects towards it. The main purpose of gravity is to pull or attract. Now we can see that pulling an object towards itself has no impact on rotation of a body. Rotation needs a torque and gravity does not provide any torque to the object.

Gravity and angular momentum relationship

As discussed in the earlier sections. There is no direct relationship of angular momentum and gravity. Gravity is simply an attractive force which pulls an object towards itself.

Angular momentum is a result of torque being applied to an object. Torque is a couple force acting on the object which produces twisting moment and helps to rotate the object. In case of gravity, mass does not pla any role in the total effect, irrespective of mass, the effect of gravity remains the same. In case of angular momentum, if mass is greater then the angular momentum is also greater considering other two factors constant.

Does momentum increase gravity?

In this article we have already laid emphasis on the relationship between gravity and momentum. And we came to a conclusion that both of them are independent of each other.

Gravity does not affect momentum in any manner. It does not increase or decrease the momentum of the object. Both linear and angular momentums are independent of gravity. Gravity, irrespective of mass has the same effect on the objects. There is a famous experiment performed by Apollo astronauts on Moon where the astronauts drop feathers and a hammer simultaneously and both of them hit the ground at the same time.

Examples of angular momentum

We can see rotating objects around us everyday. Any rotating object having mass has angular momentum.

Let us see about the different examples of angular momentum. They are given in the section given below-

  1. Rotation of Earth – The rotation of Earth is a perfect example of an object having angular acceleration. The rotational period of Earth around its axis is 24 hours. One complete rotation of Earth makes one full day.
  2. Rotating top – Tops are spinning objects on a pointed tip. These tops are given rotational motion with the help of a thread. These threads are rotated/ winded around the top, due to the unwinding, the top attains rotary motion.
  3. Toys– Some toys have elements that inside them that rotate. These rotating elements have angular momentum. The formula of angular momentum is mvr where m is the mass of rotating element, v is the velocity of rotating element and r is the radius of rotation.
  4. Revolution of Earth – Revolution of Earth around Sun is also an example of rotational motion. Hence it must also have angular momentum.
  5. Stone attached to a string– When we attach a stone around a thread and start rotating it, the stone attains angular momentum as it starts moving in rotational motion. The stone experiences centripetal force from thread and the radius of rotation will be equal to the length of the thread.
  6. Wheels of a car – While driving, the wheels follow a rotary motion. Thus it can be said that wheels have angular momentum associated with it. The radius of the wheels is the radius of rotation.
  7. Garba – While doing garba, a garba dancer rotates around a centre of rotation. Due to this the dancer attains certain amount of angular momentum as he/ she starts rotating.
  8. Ballerina– A ballerina rotates her/his body on her toes. The speed of rotation depends on the position of hands. If the hands are wide apart then the speed of rotation will be less and if the hands are placed closer to the body then the speed of rotation will be more. This explains the law of conservation of angular momentum.
  9. Ice skaters -Ice skaters rotate keeping their legs as the centre of rotation. While performing this stunt, the ice skater moves his hands closer to this body and far from his body, due to this the speed of rotation also changes. This is due to the law of conservation of angular momentum.
  10. Fan blades – When the fan is turned ON, the blades of the fan attain angular momentum. When the fan is small then it can be observed that the rotational speed is more and similarly when the blades of fans are longer then the rotational speed is less. This is due to the law of conservation of momentum.
  11. Basketball– When a basketball player spins his ball on his fingers, it can be said that the ball has attained angular momentum. The radius of rotation is same as the radius of ball. The ball rotates after the basket ball player applies torque on the ball.
  12. Frisbee– When we throw a frisbee, it attains angular momentum. The stability of frisbee depends on the rotational speed of the frisbee. As the frisbee moves forward the horizontal position of frisbee is maintained by the rotational motion.
  13. Satellite orbiting Earth– When a satellite orbits Earth, it attains angular momentum. The angular motion is governed by the same equations that we have discussed in the above sections. Even in this situation the law of conservation of angular momentum is obeyed.
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