7. How does an elastic collision differ from an inelastic collision?

The key difference between elastic and inelastic collisions lies in what happens to kinetic energy:<br /><br />* **Elastic Collision:** Kinetic energy is conserved. In a perfectly elastic collision, the total kinetic energy of the system before the collision is equal to the total kinetic energy after the collision. Think of idealized billiard balls bouncing off each other. In the real world, perfectly elastic collisions are rare at the macroscopic level, but they are a good approximation for interactions like those between gas molecules.<br /><br />* **Inelastic Collision:** Kinetic energy is *not* conserved. Some of the initial kinetic energy is transformed into other forms of energy, such as heat, sound, or deformation energy. A classic example is a car crash where the kinetic energy is converted into the energy of crumpling metal and heat. In a *perfectly inelastic* collision, the objects stick together after colliding, resulting in the maximum possible loss of kinetic energy (consistent with momentum conservation). Dropping a lump of clay onto the floor is a good approximation of a perfectly inelastic collision.<br />