Momentum

PhysicsNov 26/27

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

Exploration

• Can you figure out how to catch an egg without it breaking?

What were your results?

Topic• What did you do to

catch the egg? Did it break?

Facts

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

Momentum with Bill Nye

• Bill Nye Video

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

Create your own example

TopicHow could you

increase the momentum when hitting a volleyball?

Facts

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

Class work

• Make a plan for container that will keep your egg alive!

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

Homework

• Bring materials to build container!!!

• Read and answer ques

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

Practice Yourself

• Page 101 in your textbook, numbers 19-21

• p = mv• Impulse = Ft

Closing

TopicHow does impulse

affect changes in momentum?

Facts

Homework

1. Study the momentum notes!2. Bring materials for egg drop lab