momentum is a physics term; it refers to the quantity of motion that an object has. a sports team...

Momentum is a physics term; it refers to the quantity of motion that an object has. A sports team which is "on the move" has the momentum. If an object is in motion (on the move) then it has momentum.

More force is needed to stop a baseball thrown at 95 mph than to stop a baseball thrown at 45 mph, even though they both have the same mass

Let’s look at some examples of what momentum is

Which will have a greater momentum, me throwing a baseball at you or Roger Clements throwing it at you?

Why ?

More force is needed to stop a train than a car traveling at the same speed.

Which has more momentum, a car at 45 mph or a train at 45 mph?

Why ?

Both mass and velocity are importantfactors when considering the forceneeded to change the motion of an object.

So what factors are important for determining the momentum of an object?

This relationship was originally developedby Newton in his 2nd Law

the product ofmass and velocity

of an object

momentummomentum = = massmass x x velocityvelocity

ρρ = mv = mv

1. Determine the momentum of a ...A. 60-kg halfback moving eastward at 9 m/s. B. 1000-kg car moving northward at 20 m/s. C. 40-kg freshman moving southward at 2 m/s.

So you got the Mo?

2. A car possesses 20 000 units of momentum. What would be the car's new momentum if ...

A. its velocity were doubled. B. its velocity were tripled. C. its mass were doubled (by adding more passengers and a greater load) D. both its velocity were doubled and its mass were doubled.

An object’s momentum will change

if its mass and/or velocity changes.

According to Newton’s laws,According to Newton’s laws,a a net forcenet force causes an object to causes an object to accelerateaccelerate,,

or or change its velocitychange its velocity..

Most common… a change in velocity.What is a change in velocity called?

Acceleration a = Vf-Vo

t

F = maF = ma

Newton’s Second Law

= =

F tF t= m vm v= pp

m Vf-Vo

t

Vt

m

Impulse = change in momentumImpulse = change in momentum

FΔt = mVf-Vo

So what does this mean?

A 1000 kg car moving at 30 m/s (p = 30,000 kg m/s)A 1000 kg car moving at 30 m/s (p = 30,000 kg m/s)can be stopped bycan be stopped by

30,000 N of force 30,000 N of force acting acting for 1.0 s (a crash!) for 1.0 s (a crash!)

ororby 3000 N of force by 3000 N of force actingacting for 10.0 s (normal stop)for 10.0 s (normal stop)

Rhonda, who has a mass of 60.0 kg, is riding at 25.0 m/s in her sports car when she must suddenly slam on the brakes to avoid hitting a dog crossing the road. She strikes the air bag, which brings her body to a stop in 0.400 s. What average force does the seat belt exert on her?

If Rhonda had not been wearing her seat belt and not had an air bag, then the windshield would have stopped her head in 0.001 s. What average force would the windshield have exerted on her?

A 0.50-kg cart (#1) is pulled with a 1.0-N force for 1 sec; another 0.50 kg cart (#2) is pulled with a 2.0 N-force for 0.50 seconds.

A.Which cart (#1 or #2) has the greatest acceleration? Explain.

B. Which cart (#1 or #2) has the greatest impulse? Explain.

C. Which cart (#1 or #2) has the greatest change in momentum? Explain.

Contact time is reduced if arm's deceleration is kept as small as possible.

This is done by using "follow-through", which means to continue to push during the contact period.

Some applications of impulse

Spreading impulse out over a longer time means that the force will be less; either way, the change in momentum of the boxing glove, fist, and arm will be the same.

Observe that the greater the time over which the collision occurs, the smaller the force acting upon the object. Thus, to minimize the effect of the force on an object involved in a collision, the time must be increased; and to maximize the effect of the force on an object involved in a collision, the time must be decreased.