Does the force of friction helps us to accelerate while running? [closed]How does static friction increase with increase in the applied force?Why does the work done by an internal force differ from the work done by external force?A force is exerted on a body, kinetic energy increases but no work is done by the force. Why?Why does a conservative force return the work done against it by a body to that body?Is the work done by friction on an accelerating car zero?The direction of static friction?What is the significance of the sign of work done? Does it affect internal energy also?Running or walking up stairs = same work?Is the work-energy theorem only valid for conservative forces?Sign of the work done by dissipation forces
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Does the force of friction helps us to accelerate while running? [closed]
How does static friction increase with increase in the applied force?Why does the work done by an internal force differ from the work done by external force?A force is exerted on a body, kinetic energy increases but no work is done by the force. Why?Why does a conservative force return the work done against it by a body to that body?Is the work done by friction on an accelerating car zero?The direction of static friction?What is the significance of the sign of work done? Does it affect internal energy also?Running or walking up stairs = same work?Is the work-energy theorem only valid for conservative forces?Sign of the work done by dissipation forces
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$begingroup$
The question is to find the correct statement:
Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run.
OR
Cause of increase in kinetic energy while running is due to the work done by internal forces of the body
Book says 2nd statement is the correct one.
Why is statement 1 not correct and what are internal force?
homework-and-exercises newtonian-mechanics friction work free-body-diagram
edited Jul 3 at 21:13
Qmechanic♦
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asked Jul 3 at 17:32
Animesh SinghAnimesh Singh
233 bronze badges
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closed as off-topic by tpg2114♦ Jul 4 at 4:17
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – tpg2114
add a comment |
$begingroup$
The question is to find the correct statement:
Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run.
OR
Cause of increase in kinetic energy while running is due to the work done by internal forces of the body
Book says 2nd statement is the correct one.
Why is statement 1 not correct and what are internal force?
homework-and-exercises newtonian-mechanics friction work free-body-diagram
edited Jul 3 at 21:13
Qmechanic♦
111k12 gold badges213 silver badges1306 bronze badges
asked Jul 3 at 17:32
Animesh SinghAnimesh Singh
233 bronze badges
$endgroup$
closed as off-topic by tpg2114♦ Jul 4 at 4:17
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – tpg2114
$begingroup$
I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
$endgroup$
– Ben Crowell
Jul 3 at 17:54
add a comment |
$begingroup$
The question is to find the correct statement:
Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run.
OR
Cause of increase in kinetic energy while running is due to the work done by internal forces of the body
Book says 2nd statement is the correct one.
Why is statement 1 not correct and what are internal force?
homework-and-exercises newtonian-mechanics friction work free-body-diagram
edited Jul 3 at 21:13
Qmechanic♦
111k12 gold badges213 silver badges1306 bronze badges
asked Jul 3 at 17:32
Animesh SinghAnimesh Singh
233 bronze badges
$endgroup$
The question is to find the correct statement:
Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run.
OR
Cause of increase in kinetic energy while running is due to the work done by internal forces of the body
Book says 2nd statement is the correct one.
Why is statement 1 not correct and what are internal force?
homework-and-exercises newtonian-mechanics friction work free-body-diagram
homework-and-exercises newtonian-mechanics friction work free-body-diagram
edited Jul 3 at 21:13
Qmechanic♦
111k12 gold badges213 silver badges1306 bronze badges
asked Jul 3 at 17:32
Animesh SinghAnimesh Singh
233 bronze badges
edited Jul 3 at 21:13
Qmechanic♦
111k12 gold badges213 silver badges1306 bronze badges
asked Jul 3 at 17:32
Animesh SinghAnimesh Singh
233 bronze badges
edited Jul 3 at 21:13
Qmechanic♦
111k12 gold badges213 silver badges1306 bronze badges
edited Jul 3 at 21:13
Qmechanic♦
111k12 gold badges213 silver badges1306 bronze badges
edited Jul 3 at 21:13
Qmechanic♦
111k12 gold badges213 silver badges1306 bronze badges
111k12 gold badges213 silver badges1306 bronze badges
asked Jul 3 at 17:32
Animesh SinghAnimesh Singh
233 bronze badges
asked Jul 3 at 17:32
Animesh SinghAnimesh Singh
233 bronze badges
asked Jul 3 at 17:32
Animesh SinghAnimesh Singh
233 bronze badges
233 bronze badges
closed as off-topic by tpg2114♦ Jul 4 at 4:17
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – tpg2114
closed as off-topic by tpg2114♦ Jul 4 at 4:17
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – tpg2114
$begingroup$
I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
$endgroup$
– Ben Crowell
Jul 3 at 17:54
add a comment |
$begingroup$
I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
$endgroup$
– Ben Crowell
Jul 3 at 17:54
$begingroup$
I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
$endgroup$
– Ben Crowell
Jul 3 at 17:54
$begingroup$
I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
$endgroup$
– Ben Crowell
Jul 3 at 17:54
add a comment |
6 Answers
6
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Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.
All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.
Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.
answered Jul 3 at 17:42
Bob JacobsenBob Jacobsen
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If friction was doing work, running would be a lot more difficult.
For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.
When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.
answered Jul 3 at 18:48
JMacJMac
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Static friction just holds the foot stationary. That is all.
When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.
So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.
This is Newton's 3rd law.
answered Jul 3 at 20:08
SteevenSteeven
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1
$begingroup$
One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
$endgroup$
– JMac
Jul 3 at 20:24
add a comment |
$begingroup$
Cause of increase in kinetic energy while running is due to the work
done by friction force without which he cannot run. OR Cause of
increase in kinetic energy while running is due to the work done by
internal forces of the body
It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.
$$F_f=F_pushCosθ$$
In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.
hope this helps.
answered Jul 3 at 20:44
Bob DBob D
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add a comment |
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He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.
answered Jul 3 at 17:40
user47014user47014
1469 bronze badges
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The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.
answered Jul 3 at 17:55
Michael WalsbyMichael Walsby
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6 Answers
6
active
oldest
votes
6 Answers
6
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.
All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.
Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.
answered Jul 3 at 17:42
Bob JacobsenBob Jacobsen
6,94611 silver badges23 bronze badges
$endgroup$
add a comment |
$begingroup$
Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.
All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.
Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.
answered Jul 3 at 17:42
Bob JacobsenBob Jacobsen
6,94611 silver badges23 bronze badges
$endgroup$
add a comment |
$begingroup$
Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.
All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.
Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.
answered Jul 3 at 17:42
Bob JacobsenBob Jacobsen
6,94611 silver badges23 bronze badges
$endgroup$
Your body is accelerated by the muscles of the leg extending. That push of the leg muscle is considered an "internal" force, because it's parts of you pushing on other parts of you.
All the kinetic energy your body gains comes from that muscle extension: It's a force exerted over a distance, which does work on you. In turn, that increases your speed and kinetic energy.
Friction is what keeps your foot from moving relative to the ground, so that all the extension acts to push your body. But that friction, by itself, does no work and adds no energy.
answered Jul 3 at 17:42
Bob JacobsenBob Jacobsen
6,94611 silver badges23 bronze badges
answered Jul 3 at 17:42
Bob JacobsenBob Jacobsen
6,94611 silver badges23 bronze badges
answered Jul 3 at 17:42
Bob JacobsenBob Jacobsen
6,94611 silver badges23 bronze badges
answered Jul 3 at 17:42
Bob JacobsenBob Jacobsen
6,94611 silver badges23 bronze badges
6,94611 silver badges23 bronze badges
add a comment |
add a comment |
$begingroup$
If friction was doing work, running would be a lot more difficult.
For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.
When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.
answered Jul 3 at 18:48
JMacJMac
10.1k2 gold badges23 silver badges38 bronze badges
$endgroup$
add a comment |
$begingroup$
If friction was doing work, running would be a lot more difficult.
For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.
When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.
answered Jul 3 at 18:48
JMacJMac
10.1k2 gold badges23 silver badges38 bronze badges
$endgroup$
add a comment |
$begingroup$
If friction was doing work, running would be a lot more difficult.
For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.
When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.
answered Jul 3 at 18:48
JMacJMac
10.1k2 gold badges23 silver badges38 bronze badges
$endgroup$
If friction was doing work, running would be a lot more difficult.
For work, there needs to be force and displacement, and if there's displacement of the applied friction force, that means your feet are slipping on the surface. This slipping obviously takes away from your ability to gain forward motion.
When you are moving efficiently, there is only static friction between your feet and the ground. This is just a stationary force, and therefore no work can be done by it. The static friction allows you to convert that internal energy into kinetic energy. If the friction did work, it would actually be working against the increase in kinetic energy, via slipping.
answered Jul 3 at 18:48
JMacJMac
10.1k2 gold badges23 silver badges38 bronze badges
answered Jul 3 at 18:48
JMacJMac
10.1k2 gold badges23 silver badges38 bronze badges
answered Jul 3 at 18:48
JMacJMac
10.1k2 gold badges23 silver badges38 bronze badges
answered Jul 3 at 18:48
JMacJMac
10.1k2 gold badges23 silver badges38 bronze badges
10.1k2 gold badges23 silver badges38 bronze badges
add a comment |
add a comment |
$begingroup$
Static friction just holds the foot stationary. That is all.
When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.
So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.
This is Newton's 3rd law.
answered Jul 3 at 20:08
SteevenSteeven
28.9k8 gold badges68 silver badges119 bronze badges
$endgroup$
1
$begingroup$
One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
$endgroup$
– JMac
Jul 3 at 20:24
add a comment |
$begingroup$
Static friction just holds the foot stationary. That is all.
When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.
So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.
This is Newton's 3rd law.
answered Jul 3 at 20:08
SteevenSteeven
28.9k8 gold badges68 silver badges119 bronze badges
$endgroup$
1
$begingroup$
One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
$endgroup$
– JMac
Jul 3 at 20:24
add a comment |
$begingroup$
Static friction just holds the foot stationary. That is all.
When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.
So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.
This is Newton's 3rd law.
answered Jul 3 at 20:08
SteevenSteeven
28.9k8 gold badges68 silver badges119 bronze badges
$endgroup$
Static friction just holds the foot stationary. That is all.
When you take a step on the ground, the muscles in your leg press your foot backwards and the rest of your body forwards. Since the foot can't go backwards due to static friction, the rest of your body goes much more forwards, because the leg still must stretch as the muscles force it to.
So, basically, static friction makes it possible for you to push yourself away from the ground. But it isn't the force that actually does it. Just like you can push yourself away from a wall. That makes you speed up, not because the wall supplies any energy to you, but because the energy you put into jolting your arms backwards into the wall results in the rest of your body moving the opposite way since the arms ain't moving backwards.
This is Newton's 3rd law.
answered Jul 3 at 20:08
SteevenSteeven
28.9k8 gold badges68 silver badges119 bronze badges
edited Jul 3 at 20:13
answered Jul 3 at 20:08
SteevenSteeven
28.9k8 gold badges68 silver badges119 bronze badges
answered Jul 3 at 20:08
SteevenSteeven
28.9k8 gold badges68 silver badges119 bronze badges
answered Jul 3 at 20:08
SteevenSteeven
28.9k8 gold badges68 silver badges119 bronze badges
28.9k8 gold badges68 silver badges119 bronze badges
1
$begingroup$
One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
$endgroup$
– JMac
Jul 3 at 20:24
add a comment |
1
$begingroup$
One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
$endgroup$
– JMac
Jul 3 at 20:24
1
1
$begingroup$
One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
$endgroup$
– JMac
Jul 3 at 20:24
$begingroup$
One of the best examples I can think of to illustrate this is the difficulty of spaceflight. When travelling around Earth, we generally have stuff we can push against to gain kinetic energy from internal forces. When you're in space, there's nothing external to push against, so you have to start pushing against yourself essentially (thus ejecting fuel all the time for propulsion).
$endgroup$
– JMac
Jul 3 at 20:24
add a comment |
$begingroup$
Cause of increase in kinetic energy while running is due to the work
done by friction force without which he cannot run. OR Cause of
increase in kinetic energy while running is due to the work done by
internal forces of the body
It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.
$$F_f=F_pushCosθ$$
In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.
hope this helps.
answered Jul 3 at 20:44
Bob DBob D
10.1k3 gold badges9 silver badges34 bronze badges
$endgroup$
add a comment |
$begingroup$
Cause of increase in kinetic energy while running is due to the work
done by friction force without which he cannot run. OR Cause of
increase in kinetic energy while running is due to the work done by
internal forces of the body
It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.
$$F_f=F_pushCosθ$$
In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.
hope this helps.
answered Jul 3 at 20:44
Bob DBob D
10.1k3 gold badges9 silver badges34 bronze badges
$endgroup$
add a comment |
$begingroup$
Cause of increase in kinetic energy while running is due to the work
done by friction force without which he cannot run. OR Cause of
increase in kinetic energy while running is due to the work done by
internal forces of the body
It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.
$$F_f=F_pushCosθ$$
In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.
hope this helps.
answered Jul 3 at 20:44
Bob DBob D
10.1k3 gold badges9 silver badges34 bronze badges
$endgroup$
Cause of increase in kinetic energy while running is due to the work
done by friction force without which he cannot run. OR Cause of
increase in kinetic energy while running is due to the work done by
internal forces of the body
It is the static friction force between the runners feet and the ground that propels the runner forward. See the figure of a runner below showing the forces acting upon him and by him. It is the following static friction force shown in the figure that propels the runner foward.
$$F_f=F_pushCosθ$$
In order for the runner not to slip the friction force cannot exceed the maximum static friction force also shown in the figure.
hope this helps.
answered Jul 3 at 20:44
Bob DBob D
10.1k3 gold badges9 silver badges34 bronze badges
edited Jul 3 at 21:01
answered Jul 3 at 20:44
Bob DBob D
10.1k3 gold badges9 silver badges34 bronze badges
answered Jul 3 at 20:44
Bob DBob D
10.1k3 gold badges9 silver badges34 bronze badges
answered Jul 3 at 20:44
Bob DBob D
10.1k3 gold badges9 silver badges34 bronze badges
10.1k3 gold badges9 silver badges34 bronze badges
add a comment |
add a comment |
$begingroup$
He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.
answered Jul 3 at 17:40
user47014user47014
1469 bronze badges
$endgroup$
add a comment |
$begingroup$
He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.
answered Jul 3 at 17:40
user47014user47014
1469 bronze badges
$endgroup$
add a comment |
$begingroup$
He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.
answered Jul 3 at 17:40
user47014user47014
1469 bronze badges
$endgroup$
He wouldn't move anywhere without friction but the kinetic energy would still exist if he were flailing his legs around on wet ice.
answered Jul 3 at 17:40
user47014user47014
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answered Jul 3 at 17:40
user47014user47014
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answered Jul 3 at 17:40
user47014user47014
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answered Jul 3 at 17:40
user47014user47014
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1469 bronze badges
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The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.
answered Jul 3 at 17:55
Michael WalsbyMichael Walsby
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The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.
answered Jul 3 at 17:55
Michael WalsbyMichael Walsby
1,0071 silver badge6 bronze badges
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The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.
answered Jul 3 at 17:55
Michael WalsbyMichael Walsby
1,0071 silver badge6 bronze badges
$endgroup$
The book statement is correct. Having said that, the first statement is important, because without gravity pulling the runner toward the centre of the Earth, and the friction with the running track surface which this causes, there would be almost no increase in the runner's kinetic energy. He would be like someone in very slippery shoes trying to run on the polished surface of a freshly frozen ice rink, just floundering about and getting nowhere. So it is true to say that friction of running shoes against the ground helps runners to accelerate, but the increase in the runner's kinetic energy is due to the work done by his muscles.
answered Jul 3 at 17:55
Michael WalsbyMichael Walsby
1,0071 silver badge6 bronze badges
answered Jul 3 at 17:55
Michael WalsbyMichael Walsby
1,0071 silver badge6 bronze badges
answered Jul 3 at 17:55
Michael WalsbyMichael Walsby
1,0071 silver badge6 bronze badges
answered Jul 3 at 17:55
Michael WalsbyMichael Walsby
1,0071 silver badge6 bronze badges
1,0071 silver badge6 bronze badges
add a comment |
add a comment |
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I've added the homework-and-exercises tag. In the future, please use this tag on this type of question.
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– Ben Crowell
Jul 3 at 17:54