8. Momentum

momentum =

mass x velocity

units of momentum and impulse

Ns (newton seconds)

Impulse =

force x time

change in momentum = mv - mu

what is a direct collision

when boddies collide along thier common line of travel

priciple of conservation of linear momentum

when no external forces are present mommentum before = momentum after

When can the conservation of linear momentum not be used

When there is a collision between a particle and a fixed object eg between a wall and ball because there is an external force perpendicular to the wall so momentum is not conserved in this direction

what happens when two particles coalesce

they combine into one

is momentum a vector or scalar quantity

Vector (direction of velocity matters)

e is the

Coefficient of restitution

What values can e take

0≤e≤1

What happens when e = 1

The impact is perfectly elastic

The speed of separation = speed of approach

No kinetic energy is lost, there is perfect conservation of energy

What happens when e = 0

The impact is inelastic

The objects coalesce as they are moving together with the same speed

e =

Speed of separation/speed of approach

(v₂ - v₁)/(u₁ - u₂)

Note about e, speed of approach and separation

Only for the component of the speed that is along the line of impact

Eg if a particle collides vertically with a wall then the horizontal component of speed stays the same

Impulse using calculus

∫ F dt

Where F is force and varies over time

In a closed system if the impulse of a ball on a bat is 4Ns what is the impulse of that bat on the ball

-4Ns (the force acts in the opposite direction)

What happens to the momentum of water when it hits a solid surface

Momentum is destroyed = 0

If you work out the impulse using the change in momentum of a ball in a ball strikes bat scenario what is the impulse you have worked out acting on

Bat on the ball

In a collision between two spheres where does impulse act

Along their line of centres