Conservation of Momentum
From ZuluNotes - Free Leaving Cert Notes
| Previous: | Force, Mass and Momentum | Next: | Circular Motion | Up: | Physics |
| Conservation of Momentum | |
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| Subject: | Physics |
| Paper | 1 |
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| Level | H&O |
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The Principle of Conservation of Momentum states that in any collision between two objects, the total momentum before impact equals total momentum after impact, provided no external forces act on the system.
Note that if the two objects coalesce (stick together) after collision, then there is only one final velocity, and the above equation becomes
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Applications of the principle
- Collisions (ball games)
- Acceleration of aircraft
- Jet aircraft
Examples
Firing a gun
Before the rifle was fired there was no momentum. After the rifle was fired there was the momentum of the bullet going forward (small mass by high velocity) which equalled the momentum of the rifle going backwards (big mass by small velocity). Because they were moving in opposite directions one was positive while the other was negative so their total was again zero.
Launching a rocket
The same analysis applies to a rocket ship in space firing gas to move. In this case the small mass is the gas going in the opposite direction to the ship. This occasionally gets asked in exams.
