Elastic and inelastic collisions - Momentum

Elastic and inelastic collisions



In this lesson, we will learn:

  • Meaning of elastic and inelastic collisions
  • What happens to kinetic energy in a collision?
  • Understanding perfectly inelastic collisions
  • Problem solving with elastic and inelastic collisions


  • Total momentum and total energy are conserved in collisions. However, kinetic energy is not always conserved, since it can be converted into other forms of energy.
  • Elastic collision: collision where no kinetic energy is lost
  • Inelastic collision: collision where part of the kinetic energy is converted to other forms of energy
  • Perfectly inelastic collision: collision where the maximum possible amount of kinetic energy is converted to other forms of energy; objects stick together.

Conservation of Momentum

pi=pf\sum\vec{p}_i = \sum\vec{p}_f

pi:\vec{p}_i: initial momentum, in kilogram meters per second (kg·m/s)

pf:\vec{p}_f: final momentum, in kilogram meters per second (kg·m/s)

Conservation of Energy

Ei=Ef\sum\vec{E}_i = \sum\vec{E}_f

Ei:\vec{E}_i: initial energy, in joules (J)

Ef:\vec{E}_f: final energy, in joules (J)

Kinetic Energy

KE=12mv2KE = \frac{1}{2}mv^2

KE:KE: kinetic energy, in joules (J)

m:m: mass, in kilograms (kg)

v:v: speed, in meters per second (m/s)

Potential Energy

PE=mghPE = mgh

PE:PE: potential energy, in joules (J)

g:g: acceleration due to gravity, in meters per second squared (m/s2)

h:h: height, in meters (m)

  • Intro Lesson
    Introduction to elastic and inelastic collisions
  • 1.
    Solving word problems with momentum and elastic/inelastic collisions
  • 2.
    Ei=Ef\bold{\sum\vec{E}_i = \sum\vec{E}_f} ;\bold{ ; } pi=pf:\bold{\sum\vec{p}_i = \sum\vec{p}_f:} Conservation of energy and momentum in elastic and inelastic collisions
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Elastic and inelastic collisions

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