Which is harder to stop? ◦ A car moving at 25 m/s◦ A bicycle moving at 25 m/s

Why is it harder to stop?

Momentum can be defined as the measurement of how difficult it is to change the motion of an object.

Mathematically:◦ Momentum = (mass) * (velocity)

A sumo wrestler running towards you?A ballerina running towards you at the same speed?

What is the momentum of a 10 kg bowling ball rolling at 4 m/s?

Momentum = (mass) * (velocity) Momentum = (10 kg) * (4 m/s) Momentum = 40 kg*m/s

The units for momentum are (kg*m/s).

The units are not abbreviated into any other form (unlike Newtons)

If the momentum of an object changes, then either the mass, velocity or both has changed.

Usually, the mass of an object remains the same, so it’s the velocity that is changing.

What is the quantity that measures the change in velocity?

What causes an acceleration?

Therefore, the greater the force on an object, the greater the change in momentum.

Now for a little bit of math…

Force

=mass*accelerationvelocityinchange __

Time* Change in

momentum

Force*Time is also known as “Impulse”

A force can be used to change an object’s motion.

Impulse is how quickly or slowly that change in momentum occurs.

The amount of time it takes to change the object’s motion is called impact.

Force*Time = change in momentum To get the greatest change in momentum,

you need a greater force acting for a longer period of impact time.

Example: hitting a golf ball - http://www.youtube.com/watch?v=2Y57pw_iWlk

Example: Hitting a baseballwith a metal bat.

This is the situation where you are trying to STOP something from moving. (change the momentum to zero)

Force * Time = change in momentum

Suppose an object has very high momentum◦ How can we decrease the force the object will feel

when we try to stop the object?

Bungee jumping Air bags Boxing glove Baseball glove Pole vault mats Catching a lacrosse ball

An 8kg bowling ball traveling at 4 m/s rolls into a pillow and stops in 2 seconds. Calculate the force the pillow exerts on the bowling ball.

Force*Time = change in momentum Force*Time = mass*velocity Force*(2 seconds) = (8kg)*(4m/s) Force*(2 seconds) = 32 (kg*m/s) Force = 16 Newtons