Themes > Science > Physics > Molecular Physics > Molecular processes > Elastic and Inelastic Collisions

In this lesson we will attempt to explain the difference between elastic and inelastic collisions. If a collision between two bodies, is said to be elastic, both Momentum and kinetic energy are conserved. In the previous topic, we discovered that momentum is conserved in any system, so usually it is the conservation of kinetic energy, which determines whether or not a collision is elastic. Technically, energy is conserved in any system, but this kinetic energy can be transformed into light, heat and sound energy, and thus KE itself is not conserved.

(NOTE: Kinetic Energy (KE) refers to the energy involved with the movement of an object).

Again, we can reduce the above information to a couple of simple formulae. We simply use the formula for conservation of momentum used in the last lesson, and a new formula, to find the KE of an object. These are listed below. In an elastic collision, both of the following formulae are true:

m1u1 + m1u2 = m1v1 + m2v2

and

0.5m1u12 + 0.5m1u22 = 0.5m1v12 + 0.5m2v22

m1 = mass of object 1,

m2 = mass of object 2,

u1 = initial velocity of object 1,

u2 = initial velocity of object 2,

v1 = final velocity of object 1,

v2 = final velocity of object 2,

Note, the formula for Kinetic energy is usually represented as simply KE = 1/2mv2.


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