The Sound of Friction

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The Sound of Friction

Unit 9 Review

Conceptual Physics Unit 9: Momentum Review

Please answer these in your notebook; do not turn this in.

In addition to the questions below, you will need to be able to calculate momentum, change in momentum, impulse, force of impact, and time of impact, just like on the ranking task worksheets we completed.

1. If the time of impact in a collision is extended by four times, how does the force of impact change?

2. When you throw a ball, do you experience an impulse? What if you instead catch a ball of the same speed? What if you catch it, then throw it out again? Which impulse is greatest? (Visualize yourself on a skateboard.)

3. In terms of momentum conservation, why does a gun kick (recoil) when fired?

4. Imagine that you are hovering next to a space shuttle in orbit around the earth and your buddy of equal mass who is moving at 4 m/s with respect to the ship bumps into you. If he holds onto you, how fast do you both move with respect to the ship?

5. Everybody knows that you will be harmed less if you fall on a floor with “give” (like a firemen’s net) than a hard floor. In terms of impulse and momentum, why is this so?

6. If you throw a heavy rock from your hands while standing on a skateboard, you roll backwards. Would you roll backwards if you didn’t actually throw the rock, but went through the motions of doing so? Explain.

7. A bug and the windshield of a fast-moving car collide. Tell whether the following statements are true or false:
1. The forces of impact on the bug and on the car are the same size.
2. The impulses on the bug and on the car are the same size.
3. The changes of speed (acceleration) of the bug and of the car are the same.
4. The changes in momentum of the bug and of the car are the same size.

8. Who is in greater trouble – a person who comes to an abrupt stop when he falls to the pavement or a person that bounces from the same pavement on impact? Explain.

9. A railroad diesel engine has 4 times the mass of a flatcar. If a diesel engine coasts at 5 m/s into a flatcar that is initially at rest, how fast do the two coast after they hook together?

10. If a skater who is spinning pulls her arms in so as to reduce her moment of inertia to half of what it was, how will her rotational speed change? Explain.

11. You sit in the middle of a large, freely rotating turntable at an amusement park. If you crawl toward the outer rim, does the rotational velocity increase, decrease, or remain the same? Explain.

Momentum III

Assigned today, due Monday:

Recoil

Don't forget to turn in yesterday's homework. Today we talked about the reason a gun recoils when you fire a bullet. No homework tonight.

Momentum and Impulse Practice

Today's bellwork explained the effect of bouncing on impulse. We then had work time to complete tonight's homework - two ranking tasks about momentum:

Ranking Task: Momentum Front
Ranking Task: Momentum Back

We also passed out Concept-Development 7-1, but this will not be due at least until Friday.

Concept-Development 7-1 Front
Concept-Development 7-1 Back

Momentum and Impulse

Don't forget to turn in your homework from Friday. Tonight's homework, due tomorrow, is:

HW: Momentum II

Here are some notes about momentum and impulse from a couple of years ago:

Momentum and Impulse notes

Momentum

Today we started Unit 9: Momentum. We took some notes and practiced calculating momentum. The homework can be found in the link below and is due on Monday.

HW: Momentum I

I will try to get some notes up...I'm having trouble with the district's filter, which for some reason believes the pictures of notes that I post are "adult content." For now, you need to know that:

momentum = p
p is a vector and has the same direction as v
p units are kg*m/s
p=mv

*EDIT* Some notes!

Unit 8 Review: Circular Motion, Gravity, and Friction

Please turn in HW: Friction and count your stamps from the last two units. Below are the review problems for the Unit 8 test, which is on Thursday.

A ladybug sits halfway between the axis and the edge of a turntable. What happens to its linear speed if:

a. The RPM rate is doubled?
b. it sits on the edge of the turntable?
c. Both a and b happen?

What path would you follow if you fell off the edge of a rotating merry-go-round?

The faster the earth spins, the less a person weighs; whereas the faster a space station spins, the more a person weighs. Explain.

If the gravitational forces of the sun on the planets suddenly disappeared, in what kind of paths would they move? Be specific!

If the moon were twice as massive, would the attractive force between the earth and the moon be twice as large? Between the moon and the earth?

If you stood atop a ladder that was so tall that you were twice as far from the earth's center as you are now, how would your weight compare to its present value?

The planet Jupiter is more than 300 times as massive as Earth, so it might seem that an oject on the surface of Jupiter (if it had a surface) would weigh 300 times as much as on Earth. But it so happens that an object would scarcely weigh three times as much on the surface of Jupiter as it would on the surface of the earth. Can you come up with an explanation? (Hint: Let the terms in the equation for gravitational force guide your thinking.)

What is the cause of friction, and in what direction does it act with respect to the motion of a sliding object?

If the force of friction accting on a sliding crate is 100N, how much force must be applied to maintain a constant velocity? What will be the net force acting on the crate? What will be the acceleration?

What is the mass and what is the weight of a 10 kg object on the earth? What is its mass and weight on the moon, where the acceleration of gravity is 1/6 that of the earth?

Friction

Friday and today we talked about friction. There was no homework due today, but this was assigned and is due tomorrow. Below are some old notes that may help.

Friction Notes

Tides

If you missed the notes, the Wikipedia acticle on tides is quite good. For our class, we care about what causes the basic tides, spring tides, and neap tides. You will not be held responsible for all the details in the Wikipeida article...although the whole subject is quite fascinating.

Homework: In your own words, explain the origin of the ocean tides. Be specific and thorough!

Extra credit: There are 2 tide cycles per day and 24 hours in a day. Then why is the average period of one tide cycle 12.5 hours instead of 12 hours?

What would happen if you fell into a black hole?

Today we talked bout what would happen if you fell into a black hole. Here is a great explanation by Dr. Neil deGrasse Tyson.

Homework: Is going into a black hole a good idea? Use the Law of Universal Gravitation, but explain in your own words. NOTE: Approach this homework like an English assignment. Part of your grade will depend on the Six Traits of Writing.

Don't forget to turn in last night's homework!

HW: Universal Gravitation

Please ignore duplicate questions.

Due tomorrow for everyone:

HW: Universal Gravitation

And due Thursday for the honors class (remember that the last question is extra credit and will require research on your own):

HW: Universal Gravitation II