How do you apply conservation of momentum in a closed system?

In a closed system, the total momentum before an event is equal to the total momentum after the event.

To apply conservation of momentum in a closed system, you first need to understand what momentum is. Momentum is a measure of the motion of an object and is calculated by multiplying the object's mass by its velocity (momentum = mass × velocity). In a closed system, no external forces act on the objects within it, meaning the total momentum of the system remains constant over time.

Imagine two ice skaters pushing off each other on an ice rink. Before they push off, their combined momentum is zero if they are initially at rest. When they push off, one skater moves in one direction, and the other skater moves in the opposite direction. The momentum of one skater will be equal and opposite to the momentum of the other, ensuring the total momentum of the system remains zero, just as it was before they pushed off.

To analyse a situation using conservation of momentum, follow these steps:
1. Identify the objects involved and their masses.
2. Determine the velocities of the objects before the event.
3. Calculate the total momentum before the event by adding the individual momenta (mass × velocity) of all objects.
4. Determine the velocities of the objects after the event.
5. Calculate the total momentum after the event.
6. Ensure that the total momentum before the event equals the total momentum after the event.

For example, if a moving car collides with a stationary car, you can calculate the momentum of both cars before and after the collision. If the total momentum before the collision equals the total momentum after, you have successfully applied the conservation of momentum principle.

Remember, this principle only holds in a closed system where no external forces, like friction or air resistance, interfere. This makes it a powerful tool for understanding and predicting the outcomes of collisions and other interactions in physics.