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· Define momentum · Define impulse · Relate impulse and momentum to everyday
In life - momentum describes something “on a roll” that is difficult to stop.
In physics - momentum describes a quantity of motion.
If an object is in motion then it has momentum.
"mass in motion" Inertia Velocity
Momentum is a vector quantity. It has the same direction as the objects velocity.
p = mvEvery moving object has momentum.
To bring the object to rest we must apply a force to change this momentum to zero.
Estimate the mass of each object and estimate its velocity to try to order the following objects in increasing momentum:
footballsprinter
statue
race carskateboarder
slapshot
Bus
A textbook at rest has no momentum. To make the book move you must overcome friction and the book’s inertia by applying a force.
A force accelerates the book, giving it a velocity. The book now has forward momentum, and the inertia of the book continues the motion forward.
PHYSICS
Mome
ntum
Impulse
To change an objects motion (momentum) we need to apply an unbalanced force.
Increased momentum
Unbalanced Force
Unbalanced Force
Decreased momentum
I = F·t
The amount of unbalanced force and the time during which the force is applied is the impulse.
Impulse equals force multipled by time
F t
A force for a given amount of time will result in a mass undergoing a change in velocity.
0 m/s 10 m/s
F
F·tm·∆v
t
I = =Impulse equals a change in momentum
F·t m·∆v=
100 N
0 m/s 10 m/s
100·2 20·10= 200 200
20 kg
2 seconds
F·t m·∆v=
50 N
0 m/s10 m/s
(-50)· 20·(-10)= -200 -200
4 seconds
4
20 kg
TWO ways to apply a large impulse to an object and make a BIG change in momentum –
• apply a LARGE force for a small time,
Impulse = (Force) (time)
Impulse = (Force) (time)
• apply a small force for LONG time.
Stopping a passenger requires an impulse.
If the time can be made longer then the stopping force will be made smaller.
Small forces will cause fewer injuries to passenger.
Inertia keeps the passenger moving forward with the same momentum as before (speed of the car).
Impulse = (Force) (time)
In every sport where you hit something you are told to “follow through.”
Following through increases the TIME that your force acts on the object, which makes for a larger change in velocity (momentum)
·t m=
5000.5
=Follow through
No follow 500 =
∆vmm
F
+ 200 m/s
(.1)0.5
(.2)
+ 100 m/s
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