5.6 Momentum

Question 1

Momentum

Answer 1

p = mv

p = momentum in kilogram metre per second (kg m/s)
m = mass in kilograms (kg)
v = velocity in metres per second (m/s)

This means that an object at rest has no momentum.
Momentum keeps an object moving in the same direction, making it difficult to change the direction of an object with a large momentum.
Since velocity is a vector this means that the momentum of an object also depends on its direction of travel.
This means that momentum can be either positive or negative
If an object travelling to the right has positive momentum, an object travelling in the opposite direction (to the left) will have negative momentum.

Question 2

Conservation of momentum

Answer 2

The principle of conservation of momentum states that:
In a closed system, the total momentum before an event is equal to the total momentum after the event.
So, if two objects collide, the sum of momentum before collision = sum of momentum after the collision.
m1u1 + m2u2 = m1v1 + m2v2

Question 3

Collisions

Answer 3

Examples of momentum in an event are collisions.
Objects will either:
Collide and move in opposite directions - this is an elastic colision.
Collide and move in the same direction together - this is an inelastic collision.

Question 4

Change in momentum

Answer 4

More specifically, the force is the rate of change in momentum.
When a force acts on an object that is moving, or able to move, a change in momentum happens. Force equals the rate of change of momentum.
F = m∆v / ∆ t

Question 5

Momentum and safety

Answer 5

Since force is equal to the rate of change in momentum, the force of an impact in a vehicle collision can be decreased by increasing the contact time over which the collision occurs
The contact time is the time in which the person is in contact with what they have collided with
Therefore, safety features are created to reduce the impact of a force, such as in:
Vehicles (crumple zone, air bags and seatbelts)
Bicycle helmets
Gymnasium crashmats