Elastic Collision

Introduction:

A collision occurs when two objects come in direct contact with each other. It is the event in which two or more bodies exert forces on each other in about a relatively short time. There are two types of collisions namely :

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Elastic Collision

An elastic collision is one where there is no net loss in kinetic energy in the system due to the collision.

Inelastic Collision

An inelastic collision is a type of collision where this is a loss of kinetic energy. The lost kinetic energy is transformed into thermal energy, sound energy, and material deformation.

What is an Elastic Collision?

When two bodies collide but there is no loss in the overall kinetic energy, it is called a perfectly elastic collision. 

Elastic Collision Definition:

An elastic collision is a collision in which there is no net loss in kinetic energy in the system as a result of the collision. Both momentum and kinetic energy are conserved in an elastic collision.

Basically, in the case of collision, the kinetic energy before the collision and after the collision remains the same and is not converted to any other form of energy.

In an elastic collision, the kinetic energy before the collision and after the collision remains the same. It is not converted to other forms of energy.

It can be either one-dimensional or two-dimensional. In the real world, perfectly elastic collision is not possible because there is bound to be some conversion of energy, however small.

However, though there is no change in the linear momentum of the whole system, there is a change in the individual momenta of the involved components, which are equal and opposite in magnitude and cancel each other out and the initial energy is conserved.

Elastic Collision Examples

• When a ball at a billiard table hits another ball, it is an example of elastic collision.
• When you throw a ball on the ground and it bounces back to your hand, there is no net change in the kinetic energy and hence, it is an elastic collision.

Elastic Collision Formula

The Elastic Collision formula of momentum is given by:

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

Where,

• m₁ = Mass of 1st body
• m₂ = Mass of 2nd body
• u₁ =Initial velocity of 1st body
• u₂ = Initial velocity of the second body
• v₁ = Final velocity of the first body
• v₂ = Final velocity of the second body

The Elastic Collision formula of kinetic energy is given by:

1/2 m₁u₁² + 1/2 m₂u₂² = 1/2 m₁v₁² + 1/2 m₂v₂²

Elastic Collision Example Problem

Two billiard balls collide. Ball 1 moves with a velocity of 6 m/s, and ball 2 is at rest. After the collision, ball 1 comes to a complete stop. What is the velocity of ball 2 after the collision? Is this collision elastic or inelastic? The mass of each ball is 0.20 kg.

Solution:
To find the velocity of ball 2, use a momentum table as follows.

1.2 kg × m/s = 0.20 kg × v2

v2 =1.2 / 0.20 = 6 m/s

To determine whether the collision is elastic or inelastic, calculate the total kinetic energy of the system both before and after the collision.

Since the kinetic energy before the collision is equal to the kinetic energy after the collision (kinetic energy is conserved), this is an elastic collision.

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Difference between Elastic and Inelastic Collision

Some key differences between inelastic and elastic collisions are given below in tabular format.

Applications of Elastic Collision

• The collision time affects the amount of force that an object experiences during a collision. The greater the time over which the collision occurs, the smaller the force acting upon the object. Thus, to maximize the force experienced by an object during a collision, the collision time must be decreased.
• Likewise, to minimize the force, the collision time must be increased. There are several real-world applications of these phenomena. The airbags in automobiles increase the collapse time and minimize the effect of force on objects during a collision. Airbag accomplishes this by extending the time required to stop the momentum of the passenger and the driver.

Watch the video to learn about Coefficient-of-Restitution.

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