Question

Explain elastic waves using conservation of momentum.

Answer 1

Elastic waves:

1. Elastic waves are mechanical waves that exist in materials possessing elasticity. This is the motion created in a medium when particles are displaced. A force proportional to the displacement acts on the particles to restore them to their original position.
2. The conservation of momentum explains the conservation of energy and kinetic energy. When two or more objects collide with each other then each object exerts some force on the other for a small period of time. This force alters the momentum of the colliding objects. But the total momentum of the system remains constant.
3. In electromagnetic fields pressure exists due to the residing momentum.
4. For example, consider a short plane-wave light pulse normally incident onto a flat motionless slab. The pulse carries finite momentum in its electromagnetic fields. After reflection from the slab, the pulse imparts a normal mechanical momentum that is twice the incident pulse momentum to conserve total momentum.