BeginnerTopic 32 of 106Engineering Mechanics
Collisions
Momentum is conserved; elastic collisions also conserve kinetic energy.
In depth
Total momentum is conserved in all collisions. In elastic collisions kinetic energy is also conserved; in inelastic ones it is partly lost; in perfectly inelastic collisions bodies stick together with v=(m₁v₁+m₂v₂)/(m₁+m₂).
Key points
- Solve with momentum plus restitution
- 1D and 2D cases
- Energy lost to heat, sound and deformation
ExampleA 1000 kg car at 20 m/s hitting a stationary 1000 kg car and locking moves on at 10 m/s.
Collisions appear in crash analysis, sports and manufacturing, and momentum conservation predicts the speeds after impact without knowing the forces.
What is Collisions?
Momentum is conserved; elastic collisions also conserve kinetic energy.
Why is it important to understand collisions?
Collisions appear in crash analysis, sports and manufacturing, and momentum conservation predicts the speeds after impact without knowing the forces.
What is the difference between elastic and inelastic collisions?
Elastic collisions conserve kinetic energy as well as momentum. Inelastic collisions lose some kinetic energy to deformation and heat.
What happens in a perfectly inelastic collision?
The bodies stick together and move with a common velocity after impact, and the maximum kinetic energy is lost.
How is Collisions used in practice?
Typical applications include predicting the speeds of two vehicles after a head-on collision, analysing a ball striking a stationary target and estimating the recoil speed of a gun firing a bullet.
What should I learn before Collisions?
Study "Impulse and momentum" first (topic 31 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Collisions?
Solve with momentum plus restitution. 1D and 2D cases. Energy lost to heat, sound and deformation.
Can you give an example of Collisions?
A 1000 kg car at 20 m/s hitting a stationary 1000 kg car and locking moves on at 10 m/s.
What comes after Collisions?
The next topic is "Coefficient of restitution", which builds directly on this one.
How difficult is Collisions?
It is classed as Beginner in Engineering Mechanics (topic 32 of 106). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.