Physics Tutorial 6.6 - Collision and Impulse. Types of Collision Revision Notes

In these revision notes for Collision and Impulse. Types of Collision, we cover the following key points:

• What is impulse?
• How impulse is related to momentum?
• When does the phenomenon of impulse take place?
• How can we represent the impulse graphically?
• What is the definition of collision?
• How many types of collision arte there?
• What occurs during each type of collision?

Collision and Impulse. Types of Collision Revision Notes

In physics, Collision, also called impact, represents the sudden, forceful coming together in direct contact of two bodies, such as, for example, two balls, a hammer and a nail head, or a falling object and a floor.

There are two main types of collision. They are:

1. Elastic collision in which objects move apart after the contact, and
2. 2- Inelastic collision in which objects move together after the collision.

The highest stage of elastic collision is when an object moves at the same speed (not velocity) after the impact. This means it conserves the kinetic energy and therefore, no energy turns into other forms such as heat, sound, light (in sparks), etc. Such collision is called "absolutely (completely) elastic collision" and obviously, this is an idealization because it is clear that it is impossible not hearing any noise or not producing any heat during an impact.

"Impulse" represents the relationship between the change in momentum, collision force and time interval during which the collision occurs. Impulse is a vector quantity. It is denoted by J⃗ and it is measured by the same unit as momentum [kg × m / s], as it is obtained by subtracting the initial and final momentum of an object.

Mathematically, we have:

We can speak for impulse only during the collision; neither before, nor after it.

Newton's Second Law of Motion is often expressed in terms of impulse and time interval, i.e. as

Since in impulse the impact interval usually is very short, we take the impact force as uniform. Therefore, in the simplified version, impulse is represented by the area under the Force vs Time graph involved.

If the collision time interval is prolonged, we cannot speak anymore for impulse, as impulse takes place only when a force is exerted in a very short time interval on an object. Therefore, we cannot discuss about impulse in inelastic collision because in such collisions, the objects stick together after the impact and as a result, the impact time practically extends at infinity if no other force in the opposite direction is exerted to detach them.