Elastic & Inelastic Collisions (CIE A Level Physics)

• When two objects collide, they may spring apart retaining all of their kinetic energy. This is a perfect elastic collision
• An elastic collision is one where kinetic energy is conserved

Equation for kinetic energy

• Since kinetic energy depends on the speed of an object, in a perfectly elastic collision (head-on approach) the relative speed of approach = the relative speed of separation

• Whilst the momentum of a system is always conserved in interactions between objects, kinetic energy may not always be
• An inelastic collision is one where kinetic energy is not conserved

Equation for kinetic energy

• The kinetic energy is transferred into other forms of energy such as a heat or sound
• Inelastic collisions can be when two objects collide and they crumple and deform. Their kinetic energy may also disappear completely as they come to a halt
• A perfectly inelastic collision is when two objects stick together after collision, as shown in the example below