Objectives
• Define momentum• Define impulse and describe how it affects
changes in momentumNext Class• Solve for momentum and impulse• Explain why an impulse is greater when an
object bounces than when the same object comes to a sudden stop
Momentum
Topicmomentum
Facts• Momentum effects things in
motion• Inertia in motion• Symbol is p• p = mv– p = momentum (kg m/s)– m = mass (kg)– v = velocity (m/s)
• Also referred to as impulse
Reach for the Stars!
TopicMomentum is a
vector quantity. Why?
Facts• Because velocity is part of
momentum which is a vector quantity
• The momentum is in the same direction as the velocity
More about Impulse
TopicImpulse
Facts• Impulse is the change
momentum• The quantity force x time
Impulse = Ft• Units are Newton x seconds
(Ns)• a force applied for a longer time
period produces more change in momentum than the same force applied briefly
The relationship between momentum and impulse
TopicMomentum and
impulse
Facts
• p = mv• Impulse = FtTherefore,Ft = mv
Why?
TopicFt = mv
FactsF = ma, so we can substitute for Fmat = mv
a = v/t, therefore substitute for amvt = mv, the t’s cancel tLeaving you,mv = mv, which is why impulse equals
momentum!
Let’s See if You Understand
TopicIf you know the
momentum of an object, what else do you know?
FactsThe impulse
Something more visual• Momentum Summary (until 1:30)
Explore- increasing momentum?
TopicIf you want to hit a
home run, what would you do in order for the baseball to have the greatest momentum?
Facts• Swing as hard as
possible (force) and follow through (increases the time of contact between ball and bat)
Ft
How do you increase momentum?
TopicIncreasing momentum
Facts• Apply greatest force
for longest time
Ft
Explore- decreasing momentum?
TopicWhat did you have
to do to catch the egg without it breaking?
Refer to impulse- change time or force?
FactsI increased the time the
egg was in contact with the plate so that the change in momentum (as it falls to zero) results in less force between the egg and the plate
How do you decrease momentum?
TopicDecreasing
momentum
Facts1.Increase the amount
of impact time; therefore, decreasing the force
2.Maximize force; therefore, minimizing the impact time.
Reach for the Stars!
TopicWhat is the
relationship between force and time?
Facts
• They are inversely proportional!!!
Let’s See if You Understand
TopicWhy is falling on a
floor with more give (like carpet) less dangerous than falling on a floor with less give (like concrete)?
FactsBecause the floor with
more give (like carpet) allows a greater time for the impulse that reduces the momentum of fall to zero. A greater time for change in momentum results in less force.
Make your own example of decreasing momentum
TopicGive an example
where the momentum is decreased by increasing the impact time
Facts• Falling into a net– Increases impact time
Make your own example of decreasing momentum
TopicGive an example
where to momentum is decreased by increasing the impact force
Facts• A karate chop on a
cement block– Lots of force– Short impact time
Closing
Egg Drop Lab•When dropping the egg container, it will have momentum.
•What should your container do in order to decrease the momentum so the egg will not break?
Increase the amount of impact time; therefore, decreasing the force
Practice solving for momentum
TopicTiger woods hits a
0.05kg golf ball, giving it a speed of 75 m/s. What impulse does he impart to the ball.
FactsKnown Solve
Unknown
Equation
Practice solving for momentum
TopicIf Tiger’s golf ball rolls
onto the green 4.5 s later, what is the average force it exerted on the green.
FactsKnown Solve
Unknown
Equation
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