Reading Quiz

Question 1:

Answer:

1. The negative sighn indicates that a restoring force (F) always points in the direction opposite the distortion (x).
2. The negative sign tells us that the force is going to be in the opposite direction as the other side of the equation, which probably applies more to the direction of distortion than the spring constant itself. So, the direction of the distortion and the direction of the restoring force will be opposite.
3. The negative sign tells us that the restoring force moves in the opposite direction of the initial distortion. So if it squeezes tighter the restoring force pushes it back to its original length.
4. The negative sign shows that a restoring force always points in the direction opposite the distortion.
5. The negative sign means that the restoring force is always acting in a direction opposite to the distortion.
6. In Hooke's Law, spring constant is negative because restoring force and distortion are vectors acting in opposition (against each other, therefore when one is pulling left, the other is pushing right).
7. The negative sign means that the restoring force (the force exerted by the spring in an effort to return it to equilibrium position) is always in the direction opposite the distortion of the spring. For example, a spring distorted by being pulled down exerted a restoring force directed upward.
8. The negative sign indicates that a restoring force always points in the direction opposite the distortion.
9. the restoring force is positive when the spring is compressed, or moving in the negative direction. For when the spring is stretched, the restoring force is negative.
10. The negative sign tells us that the restoring force is in the opposite direction of the distortion.
11. The negative sign means that the restoring force is in the opposite direction as the distortion.
12. The negative sign tells us that the restoring force is always pointed opposite to the direction of the distortion.
13. It tells us that the restoring force is in the opposite direction as the force applied.
14. The negative sign in this equation tells us that a restoring force is always pointing in the direction opposite of the distortion.
15. The spring constant, k, is negative because the force that restores the spring to equilibrium must point in the opposite direction of the distortion.
16. The negative sign denoates that a restoring force points in the direction opposite the distortion.
17. The reading on the scale would increase because as your lifting the book you are exerting a force against it to overcome the downward pull of gravity, because of this the book pushes against you which is reflected in the scale.
18. This negative sign tells us that the spring's contstant (the stiffness of the spring) is always in the oppoisite direction of the distortion. This happens because the spring's stiffness is trying to pull the spring back to its equilibrium position.
19. The negative sign tells us that a "restoring" force is pointing in the direction opposite the distortion.
20. The negative sign on the distortion side of the equation indicates that the distortion is in the opposite direction from that which the restoring force points.
21. The negative sign in the equation tells us that the restoring force is pointing in the opposite direction of the distortion.
22. That a restoring force always points in the direction opposite the distortion.
23. the negative sign means the restoring force goes in the opposite direction.
24. The negative sign indicates that a restoring force always points in the direction opposite the distortion.

Question 2:

Answer:

1. The spring scale would increase because acceleration is increasing in order to get the book over your head. This acceleration means that your downward weight and the upward force from the scale no longer cancel so the spring reading increases.
2. It will remain the same. Just because you are increasing the gravitational potential energy of the book doesn't mean you are exerting any more force downward on the scale than you were before, because its mass hasn't changed and therefore its weight hasn't either.
3. I could be wrong about this, but I feel like it should stay the same because while you exert an upward force on the book it pushes back down on you, making you slightly heavier. But at the same time you are pushing up on it making it slightly lighter, and so I think the two should cancel out.
4. If you were standing on a bathroom scale and you lifted a heavy book straight up over your head the reading on the spring scale would remain the same.
5. It will may go up and down slightly because the movement of your body will cause accelerations that will cause the scale to need to rebalance. However, holding the book higher in the air will not change the weight.
6. My guess is that the reading would decrease because the book is accelerating away from the scale, so the scale requires less support force (the springs less restoring force) to hold up the book. But the scale would fluctuate if the motion was great enough to cause bouncing. I'd experiment, but my scale is digital.
7. While you lift the heavy book over your head the reading on the spring scale will remain the same. You are motionless on the scale, therefore there is no additional force introduced to the system of you standing on the scale. Energy is tranferred from you to the book you are lifting as you do work on it, but this will not affect the scale's reading.
8. I think the reading would increase because you are pushing up on the book and then you are also pushing down on the scale which would make the scale push back harder on you and would create an increase in weight.
9. The reading should increase when you first pick the book up and stay the same as you lift it over your head. Your weight, as measured by the scale, is not affected by the orientation of the mass.
10. It should remain the same because the total weight has not changed, just the position of the object to above your head.
11. remain the same because the veolcity is constant which doesn't affect the equilibrium height of the scale.
12. since the book is accelerating up, the reading on the scale will decrease.
13. Decrease
14. While the book is accelerating up, the reading on the scale will increase.
15. I think the reading on the scale will increase, but I'm not sure--I know it won't remain the same because the process of weighing is motion-sensitive.
16. It increase because the upward acceleration of the movement of the book increases an object's weight because w=mg and the force of gravity of the book increases.
17. Because the pieces of your body that stick in the furthest create the most distortion, this means that the springs are going to push back even harder to regain their equilibrium position.
18. The reading on the scale would increase because as your lifting the book you are exerting a force against it to overcome the downward pull of gravity, because of this the book pushes against you which is reflected in the scale.
19. I'm guessing it will increase.
20. While lifting the book over your head, you must do work on the book: you exert an upward force on the book, and accroding to Newton's third law the book must be exerting an equal but opposite force on you. This downward force the book exerts on you makes the reading on the spring scale increase, since a larger downward force will require a larger restoring force from the scale. However once your movement ceases, your downward weight and upward force from the scale will again cancel and the weight reading will be accurate again.
21. It will increase, since you are adding more mass and expanding its center of gravity.
22. The spring scale will increase.
23. increase
24. The reading on the spring scale will increase.

Question 3:

Answer:

1. The parts of you that stick into it the farthest are compressing the springs more. Using Hooke's law, the more the springs are compressed, the harder is pushes back.
2. All of the springs in the spring mattress are acting independently of one another, so they're acting in response to the force that the different parts of your body are putting on them. Your body's lumps are displacing the springs in certain areas more than others, so those areas feel the most force in return.
3. I would think that a large part of this is due to the fact that the human body doesnt have a center of mass located evenly in the body, so one half of your body is likely to push harder against that side of the mattress. But because of this, the parts of the body that push further into the mattress compress the springs in that area more than the areas of the body that dont push inward very much. So the forces pushing back and forth on those springs that are compressed more are stronger.
4. The spring mattress does not push up evenly on your entire body because the spring holds the greatest energy when it is compressed more. So the more a body part sticks far into the mattress, the more the spring becomes compressed and the more force it pushes back up with.
5. When parts of your body are pushing on some springs more than others, those springs are compressed much tighter than the other ones. The tighter that a spring is compressed, the greater the force it exerts will be. Those that are compressed further also have a greater force acting on them. Each spring needs to balance the force exerted upon it, and in doing so, those being acted upon the most will in turn exert more force.
6. The springs push with a force proportional to how far they have been compressesd. The force increases as you push the springs down farther, and the restoring force the spring exerts increases until the two forces reach equilibrium.
7. A spring mattress pushes most strongly on the parts of you that stick into it the farthest, and does no push up evenly on your entire body because where your body sticks in the furthest is where you are exerting the largest force on the mattress. At these points the restoring force the mattress applies on you will consequently be the largest. Every force has a force equal and opposite, therefore the place where you exert the most force on the mattress is where it will exert the largest force on you.
8. Because your body mass is distributed differently. Your center of mass or roughly the middle of your body is the heaviest part of your body and would weigh more than other parts of your body therefore the force pushing up there would be different than say down at your feet.
9. The distortion caused on the spring by your body is uneven. The more force your body exerts on one part of the mattress, the harder the springs in that part push back against you. Therefore, since your force on the mattress is uneven, its force on you is uneven as well.
10. This is because not everything of you is pushing into the mattress evenly, therefore the mattress does not push evenly back on you.
11. According the Newton's Third Law of motion, the parts of you that push down harder on the bed are being pushed up with the same but opposite force from the bed.
12. it doesn't push up evenly because of hooks law. The restoring forces by the springs on the bed are proportional to how far they are distorded from the equilibrium shape. So the springs that are pushed furthest down exert a larger force.
13. Because the further your body pushes into the mattress, the harder the mattress will push up on you. THe force the mattress applies is proportional to the distance you sink into it.
14. It pushes harder on parts that stick into the mattress farther because in those areas the springs are distorted more severely, and therefore push back with more force than parts that do not distort the springs as heavily.
15. The spring mattress exerts an upward force on you that is equal to your weight, which is the force that you are exerting on it. If parts of you exert more force on the mattress, Newton's Third Law of Motion states that the mattress will push back on those parts with an equal and opposite force.
16. You body exerts more weight on some areas of a mattress than others, and Hooke's Law says that "the restoring force exerted by an elastic object is proportional to how far it has been distorted from its equilibrium shape."
17. I thought it was pretty straightforward
18. Because the pieces of your body that stick in the furthest create the most distortion, this means that the springs are going to push back even harder to regain their equilibrium position.
19. It will push back on the parts of you that stick out the most because anything you "distort" as Hooke's law says, will push back with the same amount of force that's proportional to how far you've distorted it.
20. The parts of you that stick into the mattress the farthest have distored the spring s the most, and so the springs will exert a larger restoring force in order to return the spring to its equilibrium length. It does not push evenly up on your body because your body is not pushing evenly down on the springs, or evenly distorting the springs.
21. Because it takes more restoring force to return the heavier parts of you into equilibrium, and less for the lighter parts.
22. According to Hooke's Law, the restoring force exerted by an elastic object is proportional to how far it has been distorted. So, the parts of the body that are not distorting the mattress as much will not have as much force exerted on them by the spring.
23. You're probably lying on many springs with the same equilibrium shapes, But, each spring is being distorted from its equilibrium at different amounts because certain parts of the body are heavier than others.
24. It doesnt push up evenly on your entire body because there at different points on your body there are different wieght forces pushing down on the spring. So each spring pushes up a different way, hence the spring constant of each spring is different.

Question 4:

Answer:

1. I'd like to spend more time on how scales work. I wasn't sure about what the book was talking about with the tranfers in energy between you and a scale. I also wasn't too sure about question 2 so maybe we could go over it in class.
2. I guess I'd like to go over the answers to questions like the first two on this reading quiz, because I'm not sure I worded them exactly right, and I think I might be talking more from experience than from really understanding what's going on.
3. Could you just go over #2 on this reading quiz? Other than that I get it all.
4. Could you possibly discuss further the principle of coefficient of restitution.
5. -
6. just question #2
7. I understood the concepts in this section.
8. I was a little confused with some of the energy transfers going on with bouncing a ball...when does elastic potential energy come in? and also does any energy come from the surface the ball bounces off of?
10. equilibrium vs. motionless (described on page 88)
11. I don't understand the difference between a ball compressing and its sruface bending when it bounces. It said balls bouce best when they store energy through compression rather than surface bending, but I thought the surface always bends when a ball bounces.
12. i found the stuff about torques and measuring the piano with two scales a little bit confusing.
13. Why the scale goes back and forth when you step on it.
14. I think I understand the concepts in this reading.
15. See question 2; also, the end of the "spring scales" section, "using several scares at once" (p.89) was confusing to me.
16. None :)
17. None, thanks.
18. I thought it was pretty straightforward
19. I found this whole entire section to be confusing. I think i understood the equilibrium part. I am especially confused about the using several scales at once.
20. I had a hard time thinking through the book lifting problem. Are you accelerating during this? Also, from section 3.2, why does a lively ball waste less energy that a dead one?
21. I am a bit confused by how springs actually exert force.
22. nothing
23. none
24. hookes law and the idea of elastic PE

Question 5:

Answer:

1. Nothing at this time
2. none
3. Still have it all under control.
5. -
6. none
7. I'm okay with the previous material so far.
8. I understood everything previously in class.
10. nothing at this time.
11. nothing
12. i still am having trouble with the difference between momentum and energy
13. Nothing
14. I am not having difficulty with any material from previous classes.
15. None.
16. None
17. None, thanks.
18. Angular Impulses.
19. Angular momentum and angular impulse: can we do some example problems with numbers?
21. nothing
22. none
23. sliding and static friction