Elastic and Inelastic Collision explanation

[cks]

*** Elastic and Inelastic Collision explanation ***

1) Why energy and momentum are conserved in elastic collision?
2) Why only momentum is conserved in inelastic collision? Why energy is not conserved?

Answers:

Conservation of momentum is a consequence of Newton's third law. From the derivation, we see that only internal forces act on a system and the net external forces act on the system are zero, then we can apply conservation of momentum.

1) In the case of elastic collision, only internal forces act when the two bodies collide and come to a temporary halt and the external forces (e.g. gravitational force and normal force are zero) , so we can say firmly that momentum is conserved.


I can only explain physically why momentum is conserved for the elastic collision. I somehow couldn't find a satisfactory explanation to why energy is conserved for elastic collision and question 2.

For question 2, my textbook explains mathematically why energy is not conserved, but how about physically. A trolley that collides with another trolley and then stick together will result in a loud sound which explains why energy is not conserved. but how about if a big asteroid collideswith the earth(inelastic collision) will the energy conserved?

All suggestions and ideas are welcome. Thank you.

 

[Office_Shredder]

Energy is conserved in an elastic collision because there are no non-conservative forces acting. In an inelastic collision, heat is released when the two masses connect, no matter what the method is. It's not just sound, but also friction that the energy is lost in.

 

[kyle8921]

In an elastic collision, the kinetic energy of the system is conserved. This means that the total energy before the collision is equal to the total energy after the collision. This is because no external forces act on the system during the collision, so the total energy remains constant. In this case, both momentum and energy are conserved.

However, in an inelastic collision, some of the kinetic energy is converted into other forms of energy, such as heat, sound, or deformation of the objects involved. This means that the total energy after the collision is less than the total energy before the collision. In this case, only momentum is conserved, as the external forces acting on the system may change the total energy.

For example, in the case of a trolley collision, the sound produced is a result of the kinetic energy being converted into sound energy. In the case of a big asteroid colliding with the Earth, the impact would result in energy being released in the form of heat, sound, and seismic waves, rather than all of the kinetic energy being conserved.

In summary, the conservation of momentum and energy in collisions depends on the external forces acting on the system and the amount of energy being converted into other forms. In an elastic collision, where there are no external forces and no energy is converted, both momentum and energy are conserved. In an inelastic collision, where external forces and energy conversion are present, only momentum is conserved.