Soft Collison Is Inelastic Collison

Introduction

One of the interesting topic in physics is the mechanism of collision between different moving objects. In real life, we experience this principle on daily basis. Some of the reasons for being an interesting topics are:

1. Two main fundamental laws of nature (Principle of conservation of Momentum and Energy are involved)
2. Its wide application in engineering, especially those areas that are subject to motion and impact such as car bumpers.
3. The concept is extended to even collision between elementary particles such as proton-proton collision.
4. To get a better understanding how nature behaves.
5. And many more.

Here, in this article Collison and Interaction may be used interchangeably and both are the same.

Principle of Conservation of Momentum

Firstly, momentum of an object is defined by mass times velocity (mv). Momentum is a vector quantity.

This principle states that in any Collison regardless of how many objects and particles are involved

The total momentum of all objects before collision = The total momentum of all objects after collision

Note these points:

• This principle applies to both Linear and Angular Momenta.
• This principle applies at all levels of the universe from elementary particles, collision of vehicles, testing objects in Lab and Collison between stars and planets.
• Obviously, here we focus only on Linear Momentum.

Principle of Conservation of Energy

This is also another fundamental law of nature. In any collision between a number of objects

The Total Energy of the objects before Collison = The Total Energy of the objects After Collison

Here, Energy may be Kinetic, Potential, Heat, Nuclear, etc.

Note that Energy is a scalar quantity.

Principle of Conservation of Kinetic Energy

Indeed, at macroscopic level in collisions we are mainly interested in conservation of kinetic energy rather than the total total energy. The main focus here is kinetic energy conservation. However, at microscopic level, the total energy conservation is taken into account. But this is outside the scope of this article.

There are two different types of collisions:

Elastic Collison is a collision where the principle of conservation of kinetic energy holds, this is given by:

Total Kinetic energy of the objects before collision = Total Kinetic energy of the objects after Collison

Inelastic Collison is a collision where the principle of conservation of kinetic energy does not hold, i.e.

Total Kinetic energy of the objects before collision NOT= Total Kinetic energy of the objects after Collison

Soft Collison

Throughout this analysis, we focus only on Collison between two objects. Certainly, if we understand this for two objects, extending the concept to more should not be very difficult.

Soft collision is a collision where two objects collide and they become one object after collision OR perhaps we can put the statement in this way: they both move together.

Conclusion

Using basic principles of collision, we reached to a point that in any soft Collison, Kinetic energy is not conserved therefore, the Collison is inelastic regardless of masses and velocities of the objects involved.

Extension of this to more than two objects would not be very difficult and it requires more calculations. I shall leave this for the students to attempt.

This article is quite useful for those students who take A-Level in Physics. Usually, in exams in exam boards there are questions related to Collison and momentum.