Reading Quiz

Question 1:

Answer:

1. When I shoved/flicked the coin across the paper, it involved sliding friction. After i flicked the coin, it moved across the paper for a second and then it stopped; it did not continue to move. This is because when two surfaces (the coin, and the paper) are moving across one another, sliding friction is what stops them from sliding. When I moved the paper, and had the coin lay flat on the paper, the coin didn't move because static friction acted on them to stop them from doing such.
2. Sliding friction is involved in part A, because it occurs when two surfaces are moving across one another. While, Static Friction is involved in part B, because this keeps something from sliding across an object.
3. Case (a.) involved sliding friction just between the table and the paper, and static friction between the coin and the paper. Case (b.) involved sliding friction when the coin moved across the paper and eventually stopped.
4. Case a and b both involved sliding friction. In case a the sliding friction was between the paper and the table and in part b it was between the coin and the paper. Sliding friction deals with two surfaces moving across one another. Case a and b also had static friction. In case a the coin had static friction with the paper and in case b the static friction was between the paper and the table. This type of friction does not involve any type of movement of two objects, it is only present when two surfaces are touching.
5. Case a and b involved sliding friction: a because there was a slight sliding friction between the paper and the table as I slid it around; b because the coin was sliding across the paper and sliding friction slowed it to a stop. Case a and b involved static friction: a because static friction kept the coin in place with respect to the paper; b because my flick had to overcome the static friction between the paper and the coin to get it moving.
6. sliding friction occured when I pulled the paper slowly across the table and when I flicked the coin across the paper. Sliding friction occurs between two objects moving across each other. Static friction was the force that kept the coin in the circle when I moved the paper.
7. Case (a) involved static friction because the sufaces had the same velocity. Case (b) involved sliding friction because two surfaces were moving across one another.
8. Both cases involved sliding friction, the force that stops two surfaces from moving across one another. In case (a) the sliding friction occured between the paper and the desk. In case (b) the sliding friction occurred between the coin and the paper. Static friction was also present in both cases. In case (a) static friction existed between the coin and the paper which is why it did not move relative to the paper as the paper was pulled. In case (b) there was static friction still between the coin and the paper which you had to overcome to get the coin to move across the paper when you flicked it, but there was also static friction between the paper and the desk which prevented the paper from moving when you flicked the coin.
10. To get the paper moving across the desk, static friction had to be overcome. Once moving it turned to sliding friction. As with the paper, static friction had to be overcome in order for the coin to move after the flick, but once the static friction was overcome the friction became sliding friction.
11. Case b involves sliding friction. The penny slowed down and stopped because of the friction from sliding. Case A involves static friction. The static friction kept the penny from moving although the paper was moving.
12. a) This case involved static friction; the quarter was prevented from sliding across the paper. b) This case involved sliding friction, which stopped the quarter from sliding after it was flicked.
13. In Case (a) there was static friction, because the penny did not move on the paper, and the force that was keepin it in place was static friction. In case (b) there was sliding friction becasue the penny was moving across the paper before it came to rest.
14. In the first case, there is static friction between the coin and paper. Both objects have the same velocity, but static friction prevents them from moving. The second case involves sliding friction. Flicking the coin got the coin to move; more horizontal force was applied to it than what the paper exerted on it.
15. Sliding friction, forces that resist relative motion as two touching surfaces slide across one another, is in place when objects are already rubbing together, such as when the paper is moving across the desk and as the coin slides across the paper. Static friction, the forces that resist relative motion as outside forces try to make two touching surfaces begin to slide across one another is in place when the coin remains on the paper altought the paper is moving. It also causes the coin to slow down and slop moving across the paper.
16. To get the coin moving, you have to first exert a horizontal force on it that is greater than the static friction going the other direction. Once the penny is moving, the static friction is replaced by sliding friction. Now that the penny is moving, it experiences less horizontal force.
17. Sliding friction is involed in the second case . Static friction is involved in first case. In the first case the coin disn't slide.
18. In case (b), sliding friction acts to stop the coin from sliding across the page after you flick it-- it moves across the page when you flick it and sliding friction slows in and brings it to a stop. In case (a), statis friction acts to keep the two surfaces, the coin and the paper, from sliding across each other. The coin does not slide across the page even when you move the page, because static friction balances the force of moving the paper and the net force on the coin is zero so it remains stationary.
19. The first case only involves static friction because static friction holds the coin in place. Case b has both types of friction. Static friction has to be overcome to get the coin moving, after it gets moving sliding frictin from the paper is trying to bring it to a rest.
20. Static friction is the type of friction that takes place in part (a) because it occurs when the two objects are not moving relative to each other Sliding friction is occurring in part (b) because the coin is being shot across the paper and is moving relative to the paper.
21. Static friction is involved in the case where the penny stays in the same place on the paper because they are both moving together so friction is holding them stationary in respect to one another. Slidding is involved in the case where the penny moves independent of the paper because sliding friction is what causes the penny to slow down and stop at another point on the paper.
22. in case A, there is static friction is taking place because static friction takes place when the two objects have the same velocity, which is the case because the coin is staying in the same place and is therefore moving with the paper. In case B there is sliding friction involved because a force is acting on the coin to stop it from sliding.
23. a)When you move the paper without moving the coin out of the circle, there is sliding friction between the paper and the table and there is static friction between the coin and the paper. b)When you flick the coin out of the circle without moving the paper, static friction is overcome and sliding friction is exerted on the coin until it stops sliding.
24. Static friction was present when the coin remained stationary. That friction was what kept the coin from moving. It was also present before the coin moved in part B, and again after it came to rest. Sliding friction was only present in part B during the time that it was moving across the surface of the paper. Sliding friction is what slows an object's acceleration until it comes to rest. It was not present in the first part because the coin was not moving.

Question 2:

Answer:

1. When I flicked the coin, the force of me flicking was transferred to the coin, which made it accelerate. As the coin is sliding across the paper, it experiences a frictional force (static) that acts opposite the motion of the coin, which in turn stops it. The friction that stopped the coin converted the energy from the coin, ordered energy, into thermal energy. (i think)
2. When you flick the coin (kinetic energy) on the paper the coin accelerates and begins to move across the paper, until the friction is too great and it slows down till it finally comes to rest.
3. When the coin is at rest on the piece of paper there is static friction between the coin and the paper. When you flick it, you put a force on the coin large enough to overcome the static friction and to accelerate the coin. Once you stop touching the coin, there is sliding friction between the coin and the paper which eventually causes it to slow down and stop because it turns the kinetic energy into other kinds of disordered energy like heat.
4. The coin started at rest with static friction and gravity acting on it. The coin is pushing on the piece of paper and the table/paper is pushing up on it. After it is flicked the static friction becomes sliding friction and there is also kinetic energy present from the force of the flick. This sliding friction wastes energy, it takes ordered energy and converts it into thermal energy. The friction force makes the coin stop eventually and then it is back to the same forces that were acting on it in the beginning witht the thermal energy it gained from the friction.
5. chemical energy from your body transfers to mechanical/kinetic energy in your finger, which in turn becomes kinetic energy in the coin. The kinetic energy in the coin turns into heat energy due to friction as it slides across the paper and comes to a stop.
6. I gave the coin kinetic energy when I flicked it. The frictional force then acted in the direction opposite the flick, which slowed the coin to a stop.
7. In case (b) kinetic energy decreased as thermal energy increased. The force of the flick is pointed in the same direction as the the way the coin is moving and the frictional force is pointed in the opposite direction of the way it's moving.
8. Initially the coin was at rest, and when you flicked the coin (applied a force) it transferred chemical potential energy from your body into kinetic energy of the coin as it moved across the paper. As it slid, the force of sliding friction on the coin caused the energy to be transferred to thermal energy, until the coin ultimately slowed down and came to rest again.
10. The coin initially had solely potential energy. When I flicked it, I created a force and gave it kinetic energy. As the coin moved, friction created useless heat energy which replaced kinetic energy and slowed the coin down to an eventual stop. Gravity created the force necessary for friction by holding the coin against the paper.
11. The coin initially only had potential energy. The flick resulted in a decrease of potential energy and kenetic energy increased. Eventually potential energy increased and kenetic energy decreased as the coin slowed down. When the coin came to rest, it only had potential energy.
12. Before I touched the quarter, it had potential energy. Then I transferred kinetic energy to the quarter by flicking it; the forces involved were me pushing on the quarter and the quarter pushing back on me. Another force involved was the quarter on the earth (weight) and the earth on the quarter (gravity). Friction also acted on the quarter to slow it down and eventually stop it moving altogether. Kinetic energy also left the quarter at this time, although the quarter still had potential energy.
13. In case (b) When the coin was first flicked there was static friction holding it in place. Then once it started moving, there was sliding friction. Once the penny started moving it also had kinnetic energy. This kinnetic energy was then turned into heat energy becasue of the force of energy going in the opposite direction as the penny was moving.
14. Before flicking the coin, it has potiential energy and experiences static friction. Flicking the coin gave it kinetic energy, and so it began to move. The coin experiences sliding friction, taking away kinetic energy to create thermal energy until it is entirely converted, and comes to a standstill.
15. Your flick overcame static friction and caused there to be sliding friction between the coin and the paper. Then, static friction took over and caused the coin to stop moving.
16. This is desirable because since the 2 surfaces don't move relative to each other, there is no distance traveled and so no work is done. Static friction does not convert work into thermal energy.
17. i started out with chemical energy from my body then i transfered ot to kinetic energy, then it changed to thermal energy with friction.
18. When you flick the coin, you do work on the coin and the coin has kinetic energy in its movement path. Sliding friction converts the work into thermal energy. As energy is extracted from the sliding coin and converted into thermal energy, the coin gains thermal energy, loses kinetic energy and slows down eventually to a stop.
19. First static friction is overcome when the coin is flicked and starts moving. This gives the coin kinetic energy. Then sliding friction from the paper slows thes coin down and reduces the kinetic energy to 0.
20. The first energy transfer is the energy being transferred from your hand into the coin to make it slide -- kinetic energy is present here because of the presence fo motion. the second energy transfer is the transfer of the coins energy into the paper which makes it slow down. the third energy transfer is the thermal energy given off by the coin making it slightly warmer.
21. In case b there was an initial static friction force holding the penny in place. The force applied to the side of the penny forced it into motion by overcoming the static friction force. The force applied to the side then degraded and the penny slowed because sliding friction wastes energy.
22. Since the coin begins at rest, it begins with gravitational potential energy and zero kinetic energy. Then as you flick the coin its potential energy changes to kinetic energy. As the coin slowed down the coins kinetic energy decreases, and some of the energy is lost due to friction and therefore possibly heat and maybe sound since it makes a noise at it slides. Then as the coin returns to rest it once again has high potentinal energy and zero kinetic energy.
23. You do work on the coin and as you do work, potential energy increases. Once the coin starts moving it's kinetic energy increases and its potential energy decreases until it comes to a stop. Potential energy during the slide is also put into the thermal energy being created under coin. When it stops, there is no kinetic energy or potential energy.
24. The first energy transfer was from the stored energy in my body to the kinetic energy of my finger moving toward the coin, and then my kinetic energy transferred to the coin, setting it in motion. Then, due to the friction with the paper, part of the kinetic energy turned to thermal energy. This continued until all kinetic energy turned into thermal energy and the coin was again at rest. The forces involved were the push from my hand on the coin and the frictional force that was acting in the opposite direction as the force I exerted.

Question 3:

Answer:

1. This is desirable because static friction isn't converted into thermal energy, only sliding friction does. The "rollers, wheel and axle" only experience static friction, which keeps it cool, instead of creating heat with thermal energy.
2. Static friction is always exerting a force, therefore it balances ones push on the object and keeps the object from continuing to accelerate. When the object is moving, sliding friction comes into play. Sliding friction will slowly bring the object back to rest.
3. Sliding friction between the wheels and the ground would cause a lot of disordered energy to result. The kinetic energy of the wheels moving would be quickly drained because the sliding friction between the wheels and the surface are turned into disordered energy like heat, and the wheels would slow down to a stop fairly quickly. On the other hand, static friction loses a minimum of energy when the wheels are rolling because the part that is in contact with the
4. Static friction is more desirable because sliding friction wastes energy and causes wear to the axles. Therefore, it is best to try and minimize the sliding friction as much as possible. Also static friction between the wheels and the road is better than sliding friction because you don't want the car to skid and ruin the tires.
5. Static friction can be overcome with enough force and does not affect the wheels' motion once they are moving. Sliding friction would affect the wheels' while in motion, creating heat and slowing them down.
6. In static friction, energy is conserved between the two objects. therefore, no energy is lost. However, in sliding friction, much energy is lost due to the opposition of the frictional force, so it requires much more energy and force to move an object that is experienceing sliding friction.
7. Sliding friction wastes energy because it takes energy that cane be used to do useful work and changes it into thermal energy.
8. Experiencing only static and not sliding friction is desirable because sliding friction wastes energy by tranforming it into thermal energy in the form of heat. Therefore more force must be applied to compensate for the energy lost due to sliding friction. Static friction does not convert work into thermal energy because the two surfaces do not move in relation to each other. Therefore, energy is not wasted.
10. Static friction doesn't involve the creation of thermal energy, which is basically wasted energy. Sliding friction loses kinetic energy, while static doesn't.
11. There is no energy transformation with static friction. Sliding friction requires the transformation of potential to kenetic energy, and then kenetic energy to potential energy.
12. Sliding friction converts some work into thermal energy; while surfaces experiencing sliding friction would have a kinetic energy that wouldn't change much, the thermal energy would continue to increase. This is potentially dangerous in the case of a wheel--the involvement of sliding friction could cause overheating. Static friction, on the other hand, does not convert work into thermal energy. No work is done when two surfaces experiencing static friction don't move relative to one another and don't travel any distance.
13. The static friction that a wheel experiences is preferable to sliding friction, becasue the way a wheel works allows it to not have to ever break the static friction. If a wheel did not turn and simple was draged across the ground, it would require a lot of energy that would be turned into heat energy. However, becasue a wheel does turn, it does not convert so much of its energy into heat energy, and is much easier to move.
14. Static friction retains more kinetic energy than sliding friction. Sliding friction only leads to thermal energy. If rollers experienced only sliding friction, their work would not be as effective, and overheating and wearing down of wheels would be more common.
15. Sliding friction is weaker than static friction and has less traction. Static friction transfers more energy to the movement of the wheel and wastes less energy.
16. I would like to spend some time in class going over example problems and having more lecture time.
17. it never breaks the static friction because it is not sliding. this is better because sliding friction wastes energy by changing it into thermal energy.
18. This is desirable because static friction does not convert work into thermal energy. In absence of sliding friction, the rollers/wheels do not lose any kinetic energy and can continue at a constant velocity without having to push it.
19. This is desireable because energy would be lost if there was sliding friction, this would mean that the power was not transferred efficiently to the wheels.
20. in sliding energy, since it is wasteful, it converts usuful ordered energy into relatively useless energy called thermal energy. (Don't really understand what you are asking for in this question)
21. Experiencing only static and not sliding friction is desirable in these situations because they're all moving parts of a device which are meant to aide motion. Slidding friction wastes energy. Because they dont experience any, or as much sliding friction they dont waste as much of the energy that the input forces transfer into them. Therefore they are more efficient by minimizing the amount of sliding friction.
22. It is desirable for "the rollers, wheel and axel" to experience only static friction and not sliding friction because sliding friction wastes energy. Also sliding friction causes thermal energy, which would not be practice because it would cause heat to be given off and the wheel to become hotter. Also the use of static energy with the ground and the ground pushes horizontally on the wheels bottom to keep it from skidding.
23. With a ball bearing, the balls inside roll around the axle using only static friction. Static friction does not exert thermal energy so there is no heat created inside that will wear down the axle. Because there is only static energy, the ball bearing can last and not wear down.
24. It is desirable because sliding friction turns ordered energy into relatively useless and chaotic thermal energy. If an object is subject to sliding friction rather than static, much more force must be applied in order to keep it in motion because it loses kinetic energy.

Question 4:

Answer:

1. I just think it would be nice to have it all be explained in person, because sometimes reading it just doesn't make it sink in.
2. nothing at this time.
3. thumbs up
4. I understood the reading pretty well.
5. Does static friction exist when an object is stationary or only when something is pushing against it?
7. I was actually confused about question 2, I still havent grasped the relationship between thermal and potential and kinetic energy.
8. I understand the material in this section.
10. How sneakers against the floor create enough traction to overcome the traction of the file cabinet
11. I think the concept of the bearings was a little confusing.
12. Energy "transformations."
13. I understand most of the concepts in this reading. A review of work energy and power might be good becasue there wasnt too much about that in this reading.
14. does every stationary object have some sort of potiential energy?
15. Nada.
16. nothing in particular
17. i get it all. but i would like to go over the different types of sliding and static friction just to solidify it.
18. Can we discuss the example of the rotating police car light: the kinetic energy, rotational intertia, angular speed, etc, and solve a problem using equation 2.2.2?
19. nothing
20. sliding and static energy
21. I understand this very well I think.
22. I understand all the topics covered in the reading.
23. i'm kind of confused as to how sliding friction exerts thermal energy at the atomic level.

Question 5:

Answer:

1. I think i'm pretty much ok, although I would like to review torques.
2. I'm still a bit confused about the differences between translational and rotational motion.
3. thumbs up
4. I have understood everything so far.
5. none
7. Still a little confused about energy.
8. I am okay with everything we have discussed in class so far.
10. none
11. I think I get everything
12. Some of Friday's material, such as torque.
13. None. I think I understand all of the concepts we have covered.
14. I'm clear with past materials.
15. I had a rough time with the homework, especially finding the necessary angles in a vector diagram. Also, I do not know how to do such problems with only trig. Thanks
16. i get it all
17. I am still having some difficulty understanding torque and lever arms.
18. nothing
19. ramps and formulas for different things
20. I was unclear on 1-6 from the first homework assignment. I didn't know which formula we could use when we were only given the height of the jump?
21. The one concept i was having trouble with was the idea of torque, but I had another student in the class explain it to me with the homework, and i think i understand it now.
22. ---
23. I'm still not sure about the right-hand rule