003 ch7 impulse-slides

READ

Chapter 7.2: Impulse Changes Momentum (pp 87-91)

answer all “Questions” in the chapter

Why is it a bad idea to bungee jump with a chain?

Why is it a bad idea to bungee jump with a chain?

3.2: LEARNING TARGET 3

What will I be able to do when I’ve finished this lesson?

The student can describe impulse as a change in momentum

What idea, topic, or subject is important for me to learn and understand so that I can do this?

To be able to do this, I must learn and understand…• What impulse is• How impulse is measured• How impulse is calculated

What will I do to show that I can do this, and how well will I have to do it?

I will show my understanding of impulse by…• Identifying the units used to measure impulse• Identifying the equations used to calculate impulse• Creating a scenario showing 1) an object gaining

momentum, and 2) an object losing momentum

IMPULSE

A change in momentum!

How can we change momentum?

What would the equation for changing momentum look like?

I = ΔP = Δ(MV)

impulse = change in momentum

IMPULSE = CHANGE IN MOMENTUM

What units would this equation give us?

Describe an object that has gained momentum

Describe an object that has lost momentum

3.2: LEARNING TARGET 3

What will I be able to do when I’ve finished this lesson?

The student can describe impulse as a change in momentum

What idea, topic, or subject is important for me to learn and understand so that I can do this?

To be able to do this, I must learn and understand…• What impulse is• How impulse is measured• How impulse is calculated

What will I do to show that I can do this, and how well will I have to do it?

I will show my understanding of impulse by…• Identifying the units used to measure impulse• Identifying the equations used to calculate impulse• Creating a scenario showing 1) an object gaining

momentum, and 2) an object losing momentum

3.2: LEARNING TARGET 3

What will I do to show that I can do this, and how well will I have to do it?

I will show my understanding of impulse by…• Identifying the units used to

measure impulse• Identifying the equations used

to calculate impulse• Creating a scenario showing

1) an object gaining momentum, and 2) an object losing momentum

READ

Chapter 7.2: Impulse Changes Momentum (pp 87-91)

answer all “Questions” in the chapter

3.2: LEARNING TARGET 4

What will I be able to do when I’ve finished this lesson?

The student can describe impulse as a result of force and time

What idea, topic, or subject is important for me to learn and understand so that I can do this?

To be able to do this, I must learn and understand…• What impulse is• How impulse is related to acceleration, and thus force• How to calculate impulse in a variety of ways (using a

change in momentum, and force and time)

What will I do to show that I can do this, and how well will I have to do it?

I will show my understanding of impulse by…• Calculating impulse as it is related to force and time• Creating a scenario showing 1) an object losing

momentum quickly, and 2) an object losing momentum slowly

• Create a devise out of household objects to keep an egg from breaking when dropped from the second floor

IMPULSE AND FORCE!

What is an impulse?

What variables can change momentum?

Which of these two variables is most likely to change?

If velocity changes, what must the object be doing?

What causes acceleration?

Since an impulse is a change in momentum, and velocity is likely to change, and acceleration has to be present, which means a force must be applied, then impulse can also be calculated in terms of force!

I = FT

impulse = force X time

I = FT

Stopping requires the same impulse (change in momentum)

I = FT

Stopping requires the same impulse (change in momentum)

Stopping quickly (slamming into a brick wall) results in a small time, and large force… OUCH!!!

I = FTStopping requires the same impulse (change in momentum)

Stopping quickly (slamming into a brick wall) results in a small time, and large force… OUCH!!!

Stopping slowly (slamming into a pile of hay) results in a large stopping time and small force… WHEW!!!

Devise a way to keep an egg from breaking using household items. • Draw a sketch of your

contraption.

• Be sure you use things you actually have at your house.

Devise a way to keep an egg from breaking using household items. • Draw a sketch of your

contraption.

• Be sure you use things you actually have at your house.

PROBLEM:

A golfer swings their club with a force of 2000 N and makes contact with the ball for 0.5 seconds.

a) How much force does the ball exert back on the club?

b) How much impulse does the ball experience?

PROBLEM:

A baseball player hits a ball and makes contact for 0.25 s, giving an impulse of 875 N•s, how much force did he exert on the ball?

PROBLEM:

If a softball player exerts an impact force of 1500 N for 0.25 seconds when she strikes the ball, what is the impulse, or change in momentum, of the ball?

What if she follows through and makes contact for 0.5 seconds?

PROBLEM:

A 2200 kg SUV traveling at 94 km/h (26 m/s) can be stopped in 21 seconds by gently applying the brakes, in 5.5 seconds in a panic stop, or in 0.22 seconds if it hits a concrete wall. What average force is exerted on the SUV in each of these stops?

a. in 21 s…

b. in 5.5 s…

c. in 0.22 s…

PROBLEM:

A car moving at 10 m/s crashes into a barrier and stops in 0.050 s. There is a 20 kg child in the car. Assume that the child’s velocity is changed by the same amount as the car’s in the same time period.

a. What impulse is needed to stop the child?

b. What is the average force on the child?

c. What is the approximate mass of an object whose weight equals the force in part b.

d. Could you lift such a weight with your arms?

e. Why is it advisable to use a proper infant restraint rather that hold a child on your lap?

PROBLEM:

Small rockets are used to make tiny adjustments in the speed of satellites. One such rocket has a thrust of 35 N. If it is fired to change the velocity of a 72,000 kg spacecraft by 63 cm/s, how long should it be fired?

CALCULATING IMPULSE

impulse = change in momentum

I = Δp = Δ(mv)

impulse = force X time

I = Ft