Walking in a rotating spacecraft and Newton's 3rd Law of MotionHow deep is the force well of L4 and L5...
What is the wife of a henpecked husband called?
Does Master of Cruelties survive being blocked by a creature with 4 or more power?
What to do when being responsible for data protection in your lab, yet advice is ignored?
How to mitigate "bandwagon attacking" from players?
CBP Reminds Travelers to Allow 72 Hours for ESTA. Why?
When does inspiration across artforms become plagiarism
Unexpected behavior of Bash script: First executes function, afterwards executes alias
Is there any relevance to Thor getting his hair cut other than comedic value?
Why proton concentration is divided by 10⁻⁷?
Returning to Programming after 6 years. A little lost on how to start brushing up, what to focus on
How to satisfy a player character's curiosity about another player character?
How do ISS astronauts "get their stripes"?
Book where the good guy lives backwards through time and the bad guy lives forward
Soft question- The Bashing Technique and Other powerful techniques for Olympiads
Where is this triangular-shaped space station from?
Which aircraft had such a luxurious-looking navigator's station?
How to acknowledge an embarrassing job interview, now that I work directly with the interviewer?
How can I be pwnd if I'm not registered on that site?
Gnome Lock Screen Terminology
Quenching swords in dragon blood; why?
How to remove lines while keeping individual rows visible on a tablet
Do authors have to be politically correct in article-writing?
Should I choose Itemized or Standard deduction?
Does music exist in Panem? And if so, what kinds of music?
Walking in a rotating spacecraft and Newton's 3rd Law of Motion
How deep is the force well of L4 and L5 Lagrangian Points of Earth-Sun set?Why are there no spacecraft rotating for artificial gravity?Why do malfunctioning satellites come back to Earth?How do jetpacks work in space?Linear motion reaction wheels?Would a rotating wheel spacecraft “flip”?Atomic (Quantum) Inertial SensorIs the Parker Solar Probe's semimajor axis being so close to that of Mercury's just coincidence? Does it help somehow?Ideal shape for a long, skinny reaction mass for LEO to cis-lunar and beyond? (a “space rail gun”)Could protons in the Sun's solar wind be used to create a photonic laser thruster for a spacecraft?
$begingroup$
I am wondering how Newton's 3rd Law of Motion would apply in the case of a man walking the length of a rotating spacecraft.
Please reference the drawing below.
Say that there was a spacecraft sitting still in interstellar space, far away from any stars and planets. The spacecraft then starts to rotate via an electric motor until it reaches a rotating speed that will mimic Earth's gravity for a man inside the spacecraft. The man walks from one end of the spacecraft to the other end. While he is walking, will the spacecraft remain stationary or will the spacecraft move in the opposite direction, thus obeying Newton's 3rd Law of Motion, for every action there is an equal and opposite reaction.
Also, if the spacecraft is set in motion by the man's walking, will the spacecraft remain in motion and travel in that direction indefinitely?
EDIT
If the length of this spacecraft is extended out to 1 km long and the man is walking at 3km/hour, at this rate it will take him 20 minutes to walk from one end to the other. Now since he transferred a lot of kinetic energy to the spacecraft in those 20 minutes, the spacecraft should be moving at a good rate of speed (based on the fact that the spacecraft is constantly accelerating while he is walking).
When he reaches the other end and comes to a stop, will his body mass coming to a stop transfer enough kinetic energy back to the spacecraft to bring the spacecraft to a stop?
orbital-mechanics spacecraft physics
asked yesterday
HRIATEXPHRIATEXP
576
$endgroup$
|
show 3 more comments
$begingroup$
I am wondering how Newton's 3rd Law of Motion would apply in the case of a man walking the length of a rotating spacecraft.
Please reference the drawing below.
Say that there was a spacecraft sitting still in interstellar space, far away from any stars and planets. The spacecraft then starts to rotate via an electric motor until it reaches a rotating speed that will mimic Earth's gravity for a man inside the spacecraft. The man walks from one end of the spacecraft to the other end. While he is walking, will the spacecraft remain stationary or will the spacecraft move in the opposite direction, thus obeying Newton's 3rd Law of Motion, for every action there is an equal and opposite reaction.
Also, if the spacecraft is set in motion by the man's walking, will the spacecraft remain in motion and travel in that direction indefinitely?
EDIT
If the length of this spacecraft is extended out to 1 km long and the man is walking at 3km/hour, at this rate it will take him 20 minutes to walk from one end to the other. Now since he transferred a lot of kinetic energy to the spacecraft in those 20 minutes, the spacecraft should be moving at a good rate of speed (based on the fact that the spacecraft is constantly accelerating while he is walking).
When he reaches the other end and comes to a stop, will his body mass coming to a stop transfer enough kinetic energy back to the spacecraft to bring the spacecraft to a stop?
orbital-mechanics spacecraft physics
asked yesterday
HRIATEXPHRIATEXP
576
$endgroup$
1
$begingroup$
The system isn't balanced, I wonder if it will start to wobble and precess as much as it will move laterally, causing the person to become nauseous and run back to the corner.
$endgroup$
– uhoh
yesterday
1
$begingroup$
@HRIATEXP ah, but which will rotate, the motor or the spacecraft??
$endgroup$
– Organic Marble
yesterday
1
$begingroup$
As the man takes his first step, the craft will begin to move in the opposite direction. As he takes each step the craft will continue to move. When he takes his last step, or crashes into the end will, both he and the craft will return to rest. Given the motor (And counterweight) is massive enough to spin the man and craft without issues, the amount it will move is slight.
$endgroup$
– JCRM
yesterday
1
$begingroup$
@OrganicMarble, that's a good point. I suppose that the spacecraft could be rotated with roll thrusters instead of an electric motor.
$endgroup$
– HRIATEXP
23 hours ago
1
$begingroup$
@uhoh, I can see that may happen, he may need to take Dramamine before he starts.
$endgroup$
– HRIATEXP
23 hours ago
|
show 3 more comments
$begingroup$
I am wondering how Newton's 3rd Law of Motion would apply in the case of a man walking the length of a rotating spacecraft.
Please reference the drawing below.
Say that there was a spacecraft sitting still in interstellar space, far away from any stars and planets. The spacecraft then starts to rotate via an electric motor until it reaches a rotating speed that will mimic Earth's gravity for a man inside the spacecraft. The man walks from one end of the spacecraft to the other end. While he is walking, will the spacecraft remain stationary or will the spacecraft move in the opposite direction, thus obeying Newton's 3rd Law of Motion, for every action there is an equal and opposite reaction.
Also, if the spacecraft is set in motion by the man's walking, will the spacecraft remain in motion and travel in that direction indefinitely?
EDIT
If the length of this spacecraft is extended out to 1 km long and the man is walking at 3km/hour, at this rate it will take him 20 minutes to walk from one end to the other. Now since he transferred a lot of kinetic energy to the spacecraft in those 20 minutes, the spacecraft should be moving at a good rate of speed (based on the fact that the spacecraft is constantly accelerating while he is walking).
When he reaches the other end and comes to a stop, will his body mass coming to a stop transfer enough kinetic energy back to the spacecraft to bring the spacecraft to a stop?
orbital-mechanics spacecraft physics
asked yesterday
HRIATEXPHRIATEXP
576
$endgroup$
I am wondering how Newton's 3rd Law of Motion would apply in the case of a man walking the length of a rotating spacecraft.
Please reference the drawing below.
Say that there was a spacecraft sitting still in interstellar space, far away from any stars and planets. The spacecraft then starts to rotate via an electric motor until it reaches a rotating speed that will mimic Earth's gravity for a man inside the spacecraft. The man walks from one end of the spacecraft to the other end. While he is walking, will the spacecraft remain stationary or will the spacecraft move in the opposite direction, thus obeying Newton's 3rd Law of Motion, for every action there is an equal and opposite reaction.
Also, if the spacecraft is set in motion by the man's walking, will the spacecraft remain in motion and travel in that direction indefinitely?
EDIT
If the length of this spacecraft is extended out to 1 km long and the man is walking at 3km/hour, at this rate it will take him 20 minutes to walk from one end to the other. Now since he transferred a lot of kinetic energy to the spacecraft in those 20 minutes, the spacecraft should be moving at a good rate of speed (based on the fact that the spacecraft is constantly accelerating while he is walking).
When he reaches the other end and comes to a stop, will his body mass coming to a stop transfer enough kinetic energy back to the spacecraft to bring the spacecraft to a stop?
orbital-mechanics spacecraft physics
orbital-mechanics spacecraft physics
asked yesterday
HRIATEXPHRIATEXP
576
asked yesterday
HRIATEXPHRIATEXP
576
edited 19 hours ago
HRIATEXP
asked yesterday
HRIATEXPHRIATEXP
576
asked yesterday
HRIATEXPHRIATEXP
576
asked yesterday
HRIATEXPHRIATEXP
576
576
1
$begingroup$
The system isn't balanced, I wonder if it will start to wobble and precess as much as it will move laterally, causing the person to become nauseous and run back to the corner.
$endgroup$
– uhoh
yesterday
1
$begingroup$
@HRIATEXP ah, but which will rotate, the motor or the spacecraft??
$endgroup$
– Organic Marble
yesterday
1
$begingroup$
As the man takes his first step, the craft will begin to move in the opposite direction. As he takes each step the craft will continue to move. When he takes his last step, or crashes into the end will, both he and the craft will return to rest. Given the motor (And counterweight) is massive enough to spin the man and craft without issues, the amount it will move is slight.
$endgroup$
– JCRM
yesterday
1
$begingroup$
@OrganicMarble, that's a good point. I suppose that the spacecraft could be rotated with roll thrusters instead of an electric motor.
$endgroup$
– HRIATEXP
23 hours ago
1
$begingroup$
@uhoh, I can see that may happen, he may need to take Dramamine before he starts.
$endgroup$
– HRIATEXP
23 hours ago
|
show 3 more comments
1
$begingroup$
The system isn't balanced, I wonder if it will start to wobble and precess as much as it will move laterally, causing the person to become nauseous and run back to the corner.
$endgroup$
– uhoh
yesterday
1
$begingroup$
@HRIATEXP ah, but which will rotate, the motor or the spacecraft??
$endgroup$
– Organic Marble
yesterday
1
$begingroup$
As the man takes his first step, the craft will begin to move in the opposite direction. As he takes each step the craft will continue to move. When he takes his last step, or crashes into the end will, both he and the craft will return to rest. Given the motor (And counterweight) is massive enough to spin the man and craft without issues, the amount it will move is slight.
$endgroup$
– JCRM
yesterday
1
$begingroup$
@OrganicMarble, that's a good point. I suppose that the spacecraft could be rotated with roll thrusters instead of an electric motor.
$endgroup$
– HRIATEXP
23 hours ago
1
$begingroup$
@uhoh, I can see that may happen, he may need to take Dramamine before he starts.
$endgroup$
– HRIATEXP
23 hours ago
1
1
$begingroup$
The system isn't balanced, I wonder if it will start to wobble and precess as much as it will move laterally, causing the person to become nauseous and run back to the corner.
$endgroup$
– uhoh
yesterday
$begingroup$
The system isn't balanced, I wonder if it will start to wobble and precess as much as it will move laterally, causing the person to become nauseous and run back to the corner.
$endgroup$
– uhoh
yesterday
1
1
$begingroup$
@HRIATEXP ah, but which will rotate, the motor or the spacecraft??
$endgroup$
– Organic Marble
yesterday
$begingroup$
@HRIATEXP ah, but which will rotate, the motor or the spacecraft??
$endgroup$
– Organic Marble
yesterday
1
1
$begingroup$
As the man takes his first step, the craft will begin to move in the opposite direction. As he takes each step the craft will continue to move. When he takes his last step, or crashes into the end will, both he and the craft will return to rest. Given the motor (And counterweight) is massive enough to spin the man and craft without issues, the amount it will move is slight.
$endgroup$
– JCRM
yesterday
$begingroup$
As the man takes his first step, the craft will begin to move in the opposite direction. As he takes each step the craft will continue to move. When he takes his last step, or crashes into the end will, both he and the craft will return to rest. Given the motor (And counterweight) is massive enough to spin the man and craft without issues, the amount it will move is slight.
$endgroup$
– JCRM
yesterday
1
1
$begingroup$
@OrganicMarble, that's a good point. I suppose that the spacecraft could be rotated with roll thrusters instead of an electric motor.
$endgroup$
– HRIATEXP
23 hours ago
$begingroup$
@OrganicMarble, that's a good point. I suppose that the spacecraft could be rotated with roll thrusters instead of an electric motor.
$endgroup$
– HRIATEXP
23 hours ago
1
1
$begingroup$
@uhoh, I can see that may happen, he may need to take Dramamine before he starts.
$endgroup$
– HRIATEXP
23 hours ago
$begingroup$
@uhoh, I can see that may happen, he may need to take Dramamine before he starts.
$endgroup$
– HRIATEXP
23 hours ago
|
show 3 more comments
3 Answers
3
active
oldest
votes
$begingroup$
In the frame of reference where the spacecraft is initially at rest, the momentum of the spacecraft (including you) will initially be zero. By conservation of momentum, it will continue to be zero the entire time you are walking and after you have stopped.
While you are walking, you will have a certain amount of momentum in your forward direction. Because the total momentum of the spacecraft-plus-you is zero, the spacecraft will have momentum of the same magnitude in the opposite direction. This means it will be moving very slowly towards your rear. Because it is much more massive than you, it will be moving backwards proportionally more slowly. Somebody watching from the outside would not be able to notice the motion.
Once you got to the other end, as you stopped moving forwards, it would stop moving backwards, thus keeping the net momentum at zero. This would be true no matter how you moved around inside the spacecraft before stopping.
It is wrong to think that you will be continually transferring kinetic energy while you are walking. You transfer a small amount as you accelerate to your walking speed, and then you perform no additional (net) work on the spacecraft until you stop. The momentum has to balance.
The effort you put into walking is to make up for frictional losses in your joints and against the ground, and it all gets turned into heat.
answered 16 hours ago
Mark FoskeyMark Foskey
2,140917
$endgroup$
$begingroup$
@ Mark Foskey, very good explanation. This pretty much answers my initial question of whether the spacecraft would stay stationary or would be put in motion while the man is walking. I'm curious about one thing though...would the same hold true if say the man was to ride a segway instead of walking? Would riding on wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
1
$begingroup$
@HRIATEXP: No, the whole argument just talks about momentum transfer between the person and the spacecraft. If we looked in detail at steps we could see that the motion of the spacecraft had some steppiness to it, which the segway would presumably remove, but this answer does not consider that. The segway would start at the beginning and stop at the end just like the walker.
$endgroup$
– Ross Millikan
14 hours ago
add a comment |
$begingroup$
The spacecraft + astronaut can be treated as a system where the center of mass is moving. When the astronaut stops, the space station stops its astronaut-induced motion, because the momentum in that system is conserved.
The Third Law is how momentum is transferred between the parts of that system, but conservation of momentum is going to dictate the velocity of those parts relative to one another.
answered 18 hours ago
Erin AnneErin Anne
2,450430
$endgroup$
$begingroup$
@ Erin Anne, thanks for pointing that out. One thing though, the spacecraft and the astronaut should be in motion at the point where he stops walking. Is it correct in saying that the spacecraft should slowly decelerate for a time before coming to a dead stop as opposed to it making an immediate dead stop when he stops walking?
$endgroup$
– HRIATEXP
17 hours ago
1
$begingroup$
The station continuing to have velocity from the astronaut's walking would imply that the astronaut still has velocity too. If the astronaut has stopped walking, the astronaut has also stopped moving the space station.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
@ Erin Anne, okay
$endgroup$
– HRIATEXP
17 hours ago
2
$begingroup$
To put it another way: If the astronaut COULD be stopped with the space station still moving, the astronaut could start again before the space station stops. How much more energy would the space station gain? How much longer would it take before the space station stopped? Eventually the space station wouldn't need thrusters anymore, just something moving back and forth inside. In the universe we live in, this doesn't work.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
What about friction? If more energy is lost due to heat by walking than by stopping, wouldn't that result in a net difference?
$endgroup$
– vsz
13 hours ago
|
show 1 more comment
$begingroup$
I think your confusion might be based around your contention that
he transferred a lot of kinetic energy to the spacecraft in those 20 minutes
Instead of considering the entire walk, consider each step. The astronaut is pushing against the "floor," and as he moves forward the spacecraft moves in the opposite direction such that momentum (in the spacecraft-astronaut system) is conserved. If he then stops, the station will stop as well. If he puts his opposite leg forward to take another step it is the same (momentum-wise) as if he stopped before taking another step. Prove this to yourself by considering a treadmill: as you walk the speed of the treadmill stays constant - it does not accelerate. Considering each step as a discrete action makes it more clear that he is not continually imparting more and more velocity to the spacecraft (remember, in the frame of the spacecraft he isn't accelerating once he begins walking at 3km/hr).
Maybe a simpler way to consider this that doesn't require kinesiology is the case in which the astronaut floats in the center at one end and pushes off with his legs towards the other end (left to right in your figure). The same forces are at play; he has essentially just imparted some velocity to the spacecraft in the opposite direction of his motion. If there were a hole at the right end of the figure he would shoot out into the void and the spacecraft would continue with the (relatively small) increased velocity. If we replace the jumping with a controlled explosion and the astronaut with exhaust, this is how rocket engines work. If we patch the hole and he hits the wall, he and the spacecraft will lose the velocity induced by the original jump and the system is as it was originally.
answered 16 hours ago
benben
391210
$endgroup$
$begingroup$
@ ben, I realize now how walking will not cause the spacecraft to be continually accelerated due to a kinetic energy transfer. I am curious about one thing, and I asked the user 'Mark Foskey' the same question...if say the man was to ride on a segway instead of walking, would riding on powered wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
$begingroup$
no @HRIATEXP , except wheels are much less inefficient than walking, so the whole thing will be a lot smoother
$endgroup$
– JCRM
7 hours ago
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "508"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fspace.stackexchange.com%2fquestions%2f34590%2fwalking-in-a-rotating-spacecraft-and-newtons-3rd-law-of-motion%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
In the frame of reference where the spacecraft is initially at rest, the momentum of the spacecraft (including you) will initially be zero. By conservation of momentum, it will continue to be zero the entire time you are walking and after you have stopped.
While you are walking, you will have a certain amount of momentum in your forward direction. Because the total momentum of the spacecraft-plus-you is zero, the spacecraft will have momentum of the same magnitude in the opposite direction. This means it will be moving very slowly towards your rear. Because it is much more massive than you, it will be moving backwards proportionally more slowly. Somebody watching from the outside would not be able to notice the motion.
Once you got to the other end, as you stopped moving forwards, it would stop moving backwards, thus keeping the net momentum at zero. This would be true no matter how you moved around inside the spacecraft before stopping.
It is wrong to think that you will be continually transferring kinetic energy while you are walking. You transfer a small amount as you accelerate to your walking speed, and then you perform no additional (net) work on the spacecraft until you stop. The momentum has to balance.
The effort you put into walking is to make up for frictional losses in your joints and against the ground, and it all gets turned into heat.
answered 16 hours ago
Mark FoskeyMark Foskey
2,140917
$endgroup$
$begingroup$
@ Mark Foskey, very good explanation. This pretty much answers my initial question of whether the spacecraft would stay stationary or would be put in motion while the man is walking. I'm curious about one thing though...would the same hold true if say the man was to ride a segway instead of walking? Would riding on wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
1
$begingroup$
@HRIATEXP: No, the whole argument just talks about momentum transfer between the person and the spacecraft. If we looked in detail at steps we could see that the motion of the spacecraft had some steppiness to it, which the segway would presumably remove, but this answer does not consider that. The segway would start at the beginning and stop at the end just like the walker.
$endgroup$
– Ross Millikan
14 hours ago
add a comment |
$begingroup$
In the frame of reference where the spacecraft is initially at rest, the momentum of the spacecraft (including you) will initially be zero. By conservation of momentum, it will continue to be zero the entire time you are walking and after you have stopped.
While you are walking, you will have a certain amount of momentum in your forward direction. Because the total momentum of the spacecraft-plus-you is zero, the spacecraft will have momentum of the same magnitude in the opposite direction. This means it will be moving very slowly towards your rear. Because it is much more massive than you, it will be moving backwards proportionally more slowly. Somebody watching from the outside would not be able to notice the motion.
Once you got to the other end, as you stopped moving forwards, it would stop moving backwards, thus keeping the net momentum at zero. This would be true no matter how you moved around inside the spacecraft before stopping.
It is wrong to think that you will be continually transferring kinetic energy while you are walking. You transfer a small amount as you accelerate to your walking speed, and then you perform no additional (net) work on the spacecraft until you stop. The momentum has to balance.
The effort you put into walking is to make up for frictional losses in your joints and against the ground, and it all gets turned into heat.
answered 16 hours ago
Mark FoskeyMark Foskey
2,140917
$endgroup$
$begingroup$
@ Mark Foskey, very good explanation. This pretty much answers my initial question of whether the spacecraft would stay stationary or would be put in motion while the man is walking. I'm curious about one thing though...would the same hold true if say the man was to ride a segway instead of walking? Would riding on wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
1
$begingroup$
@HRIATEXP: No, the whole argument just talks about momentum transfer between the person and the spacecraft. If we looked in detail at steps we could see that the motion of the spacecraft had some steppiness to it, which the segway would presumably remove, but this answer does not consider that. The segway would start at the beginning and stop at the end just like the walker.
$endgroup$
– Ross Millikan
14 hours ago
add a comment |
$begingroup$
In the frame of reference where the spacecraft is initially at rest, the momentum of the spacecraft (including you) will initially be zero. By conservation of momentum, it will continue to be zero the entire time you are walking and after you have stopped.
While you are walking, you will have a certain amount of momentum in your forward direction. Because the total momentum of the spacecraft-plus-you is zero, the spacecraft will have momentum of the same magnitude in the opposite direction. This means it will be moving very slowly towards your rear. Because it is much more massive than you, it will be moving backwards proportionally more slowly. Somebody watching from the outside would not be able to notice the motion.
Once you got to the other end, as you stopped moving forwards, it would stop moving backwards, thus keeping the net momentum at zero. This would be true no matter how you moved around inside the spacecraft before stopping.
It is wrong to think that you will be continually transferring kinetic energy while you are walking. You transfer a small amount as you accelerate to your walking speed, and then you perform no additional (net) work on the spacecraft until you stop. The momentum has to balance.
The effort you put into walking is to make up for frictional losses in your joints and against the ground, and it all gets turned into heat.
answered 16 hours ago
Mark FoskeyMark Foskey
2,140917
$endgroup$
In the frame of reference where the spacecraft is initially at rest, the momentum of the spacecraft (including you) will initially be zero. By conservation of momentum, it will continue to be zero the entire time you are walking and after you have stopped.
While you are walking, you will have a certain amount of momentum in your forward direction. Because the total momentum of the spacecraft-plus-you is zero, the spacecraft will have momentum of the same magnitude in the opposite direction. This means it will be moving very slowly towards your rear. Because it is much more massive than you, it will be moving backwards proportionally more slowly. Somebody watching from the outside would not be able to notice the motion.
Once you got to the other end, as you stopped moving forwards, it would stop moving backwards, thus keeping the net momentum at zero. This would be true no matter how you moved around inside the spacecraft before stopping.
It is wrong to think that you will be continually transferring kinetic energy while you are walking. You transfer a small amount as you accelerate to your walking speed, and then you perform no additional (net) work on the spacecraft until you stop. The momentum has to balance.
The effort you put into walking is to make up for frictional losses in your joints and against the ground, and it all gets turned into heat.
answered 16 hours ago
Mark FoskeyMark Foskey
2,140917
answered 16 hours ago
Mark FoskeyMark Foskey
2,140917
answered 16 hours ago
Mark FoskeyMark Foskey
2,140917
answered 16 hours ago
Mark FoskeyMark Foskey
2,140917
2,140917
$begingroup$
@ Mark Foskey, very good explanation. This pretty much answers my initial question of whether the spacecraft would stay stationary or would be put in motion while the man is walking. I'm curious about one thing though...would the same hold true if say the man was to ride a segway instead of walking? Would riding on wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
1
$begingroup$
@HRIATEXP: No, the whole argument just talks about momentum transfer between the person and the spacecraft. If we looked in detail at steps we could see that the motion of the spacecraft had some steppiness to it, which the segway would presumably remove, but this answer does not consider that. The segway would start at the beginning and stop at the end just like the walker.
$endgroup$
– Ross Millikan
14 hours ago
add a comment |
$begingroup$
@ Mark Foskey, very good explanation. This pretty much answers my initial question of whether the spacecraft would stay stationary or would be put in motion while the man is walking. I'm curious about one thing though...would the same hold true if say the man was to ride a segway instead of walking? Would riding on wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
1
$begingroup$
@HRIATEXP: No, the whole argument just talks about momentum transfer between the person and the spacecraft. If we looked in detail at steps we could see that the motion of the spacecraft had some steppiness to it, which the segway would presumably remove, but this answer does not consider that. The segway would start at the beginning and stop at the end just like the walker.
$endgroup$
– Ross Millikan
14 hours ago
$begingroup$
@ Mark Foskey, very good explanation. This pretty much answers my initial question of whether the spacecraft would stay stationary or would be put in motion while the man is walking. I'm curious about one thing though...would the same hold true if say the man was to ride a segway instead of walking? Would riding on wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
$begingroup$
@ Mark Foskey, very good explanation. This pretty much answers my initial question of whether the spacecraft would stay stationary or would be put in motion while the man is walking. I'm curious about one thing though...would the same hold true if say the man was to ride a segway instead of walking? Would riding on wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
1
1
$begingroup$
@HRIATEXP: No, the whole argument just talks about momentum transfer between the person and the spacecraft. If we looked in detail at steps we could see that the motion of the spacecraft had some steppiness to it, which the segway would presumably remove, but this answer does not consider that. The segway would start at the beginning and stop at the end just like the walker.
$endgroup$
– Ross Millikan
14 hours ago
$begingroup$
@HRIATEXP: No, the whole argument just talks about momentum transfer between the person and the spacecraft. If we looked in detail at steps we could see that the motion of the spacecraft had some steppiness to it, which the segway would presumably remove, but this answer does not consider that. The segway would start at the beginning and stop at the end just like the walker.
$endgroup$
– Ross Millikan
14 hours ago
add a comment |
$begingroup$
The spacecraft + astronaut can be treated as a system where the center of mass is moving. When the astronaut stops, the space station stops its astronaut-induced motion, because the momentum in that system is conserved.
The Third Law is how momentum is transferred between the parts of that system, but conservation of momentum is going to dictate the velocity of those parts relative to one another.
answered 18 hours ago
Erin AnneErin Anne
2,450430
$endgroup$
$begingroup$
@ Erin Anne, thanks for pointing that out. One thing though, the spacecraft and the astronaut should be in motion at the point where he stops walking. Is it correct in saying that the spacecraft should slowly decelerate for a time before coming to a dead stop as opposed to it making an immediate dead stop when he stops walking?
$endgroup$
– HRIATEXP
17 hours ago
1
$begingroup$
The station continuing to have velocity from the astronaut's walking would imply that the astronaut still has velocity too. If the astronaut has stopped walking, the astronaut has also stopped moving the space station.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
@ Erin Anne, okay
$endgroup$
– HRIATEXP
17 hours ago
2
$begingroup$
To put it another way: If the astronaut COULD be stopped with the space station still moving, the astronaut could start again before the space station stops. How much more energy would the space station gain? How much longer would it take before the space station stopped? Eventually the space station wouldn't need thrusters anymore, just something moving back and forth inside. In the universe we live in, this doesn't work.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
What about friction? If more energy is lost due to heat by walking than by stopping, wouldn't that result in a net difference?
$endgroup$
– vsz
13 hours ago
|
show 1 more comment
$begingroup$
The spacecraft + astronaut can be treated as a system where the center of mass is moving. When the astronaut stops, the space station stops its astronaut-induced motion, because the momentum in that system is conserved.
The Third Law is how momentum is transferred between the parts of that system, but conservation of momentum is going to dictate the velocity of those parts relative to one another.
answered 18 hours ago
Erin AnneErin Anne
2,450430
$endgroup$
$begingroup$
@ Erin Anne, thanks for pointing that out. One thing though, the spacecraft and the astronaut should be in motion at the point where he stops walking. Is it correct in saying that the spacecraft should slowly decelerate for a time before coming to a dead stop as opposed to it making an immediate dead stop when he stops walking?
$endgroup$
– HRIATEXP
17 hours ago
1
$begingroup$
The station continuing to have velocity from the astronaut's walking would imply that the astronaut still has velocity too. If the astronaut has stopped walking, the astronaut has also stopped moving the space station.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
@ Erin Anne, okay
$endgroup$
– HRIATEXP
17 hours ago
2
$begingroup$
To put it another way: If the astronaut COULD be stopped with the space station still moving, the astronaut could start again before the space station stops. How much more energy would the space station gain? How much longer would it take before the space station stopped? Eventually the space station wouldn't need thrusters anymore, just something moving back and forth inside. In the universe we live in, this doesn't work.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
What about friction? If more energy is lost due to heat by walking than by stopping, wouldn't that result in a net difference?
$endgroup$
– vsz
13 hours ago
|
show 1 more comment
$begingroup$
The spacecraft + astronaut can be treated as a system where the center of mass is moving. When the astronaut stops, the space station stops its astronaut-induced motion, because the momentum in that system is conserved.
The Third Law is how momentum is transferred between the parts of that system, but conservation of momentum is going to dictate the velocity of those parts relative to one another.
answered 18 hours ago
Erin AnneErin Anne
2,450430
$endgroup$
The spacecraft + astronaut can be treated as a system where the center of mass is moving. When the astronaut stops, the space station stops its astronaut-induced motion, because the momentum in that system is conserved.
The Third Law is how momentum is transferred between the parts of that system, but conservation of momentum is going to dictate the velocity of those parts relative to one another.
answered 18 hours ago
Erin AnneErin Anne
2,450430
answered 18 hours ago
Erin AnneErin Anne
2,450430
answered 18 hours ago
Erin AnneErin Anne
2,450430
answered 18 hours ago
Erin AnneErin Anne
2,450430
2,450430
$begingroup$
@ Erin Anne, thanks for pointing that out. One thing though, the spacecraft and the astronaut should be in motion at the point where he stops walking. Is it correct in saying that the spacecraft should slowly decelerate for a time before coming to a dead stop as opposed to it making an immediate dead stop when he stops walking?
$endgroup$
– HRIATEXP
17 hours ago
1
$begingroup$
The station continuing to have velocity from the astronaut's walking would imply that the astronaut still has velocity too. If the astronaut has stopped walking, the astronaut has also stopped moving the space station.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
@ Erin Anne, okay
$endgroup$
– HRIATEXP
17 hours ago
2
$begingroup$
To put it another way: If the astronaut COULD be stopped with the space station still moving, the astronaut could start again before the space station stops. How much more energy would the space station gain? How much longer would it take before the space station stopped? Eventually the space station wouldn't need thrusters anymore, just something moving back and forth inside. In the universe we live in, this doesn't work.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
What about friction? If more energy is lost due to heat by walking than by stopping, wouldn't that result in a net difference?
$endgroup$
– vsz
13 hours ago
|
show 1 more comment
$begingroup$
@ Erin Anne, thanks for pointing that out. One thing though, the spacecraft and the astronaut should be in motion at the point where he stops walking. Is it correct in saying that the spacecraft should slowly decelerate for a time before coming to a dead stop as opposed to it making an immediate dead stop when he stops walking?
$endgroup$
– HRIATEXP
17 hours ago
1
$begingroup$
The station continuing to have velocity from the astronaut's walking would imply that the astronaut still has velocity too. If the astronaut has stopped walking, the astronaut has also stopped moving the space station.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
@ Erin Anne, okay
$endgroup$
– HRIATEXP
17 hours ago
2
$begingroup$
To put it another way: If the astronaut COULD be stopped with the space station still moving, the astronaut could start again before the space station stops. How much more energy would the space station gain? How much longer would it take before the space station stopped? Eventually the space station wouldn't need thrusters anymore, just something moving back and forth inside. In the universe we live in, this doesn't work.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
What about friction? If more energy is lost due to heat by walking than by stopping, wouldn't that result in a net difference?
$endgroup$
– vsz
13 hours ago
$begingroup$
@ Erin Anne, thanks for pointing that out. One thing though, the spacecraft and the astronaut should be in motion at the point where he stops walking. Is it correct in saying that the spacecraft should slowly decelerate for a time before coming to a dead stop as opposed to it making an immediate dead stop when he stops walking?
$endgroup$
– HRIATEXP
17 hours ago
$begingroup$
@ Erin Anne, thanks for pointing that out. One thing though, the spacecraft and the astronaut should be in motion at the point where he stops walking. Is it correct in saying that the spacecraft should slowly decelerate for a time before coming to a dead stop as opposed to it making an immediate dead stop when he stops walking?
$endgroup$
– HRIATEXP
17 hours ago
1
1
$begingroup$
The station continuing to have velocity from the astronaut's walking would imply that the astronaut still has velocity too. If the astronaut has stopped walking, the astronaut has also stopped moving the space station.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
The station continuing to have velocity from the astronaut's walking would imply that the astronaut still has velocity too. If the astronaut has stopped walking, the astronaut has also stopped moving the space station.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
@ Erin Anne, okay
$endgroup$
– HRIATEXP
17 hours ago
$begingroup$
@ Erin Anne, okay
$endgroup$
– HRIATEXP
17 hours ago
2
2
$begingroup$
To put it another way: If the astronaut COULD be stopped with the space station still moving, the astronaut could start again before the space station stops. How much more energy would the space station gain? How much longer would it take before the space station stopped? Eventually the space station wouldn't need thrusters anymore, just something moving back and forth inside. In the universe we live in, this doesn't work.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
To put it another way: If the astronaut COULD be stopped with the space station still moving, the astronaut could start again before the space station stops. How much more energy would the space station gain? How much longer would it take before the space station stopped? Eventually the space station wouldn't need thrusters anymore, just something moving back and forth inside. In the universe we live in, this doesn't work.
$endgroup$
– Erin Anne
17 hours ago
$begingroup$
What about friction? If more energy is lost due to heat by walking than by stopping, wouldn't that result in a net difference?
$endgroup$
– vsz
13 hours ago
$begingroup$
What about friction? If more energy is lost due to heat by walking than by stopping, wouldn't that result in a net difference?
$endgroup$
– vsz
13 hours ago
|
show 1 more comment
$begingroup$
I think your confusion might be based around your contention that
he transferred a lot of kinetic energy to the spacecraft in those 20 minutes
Instead of considering the entire walk, consider each step. The astronaut is pushing against the "floor," and as he moves forward the spacecraft moves in the opposite direction such that momentum (in the spacecraft-astronaut system) is conserved. If he then stops, the station will stop as well. If he puts his opposite leg forward to take another step it is the same (momentum-wise) as if he stopped before taking another step. Prove this to yourself by considering a treadmill: as you walk the speed of the treadmill stays constant - it does not accelerate. Considering each step as a discrete action makes it more clear that he is not continually imparting more and more velocity to the spacecraft (remember, in the frame of the spacecraft he isn't accelerating once he begins walking at 3km/hr).
Maybe a simpler way to consider this that doesn't require kinesiology is the case in which the astronaut floats in the center at one end and pushes off with his legs towards the other end (left to right in your figure). The same forces are at play; he has essentially just imparted some velocity to the spacecraft in the opposite direction of his motion. If there were a hole at the right end of the figure he would shoot out into the void and the spacecraft would continue with the (relatively small) increased velocity. If we replace the jumping with a controlled explosion and the astronaut with exhaust, this is how rocket engines work. If we patch the hole and he hits the wall, he and the spacecraft will lose the velocity induced by the original jump and the system is as it was originally.
answered 16 hours ago
benben
391210
$endgroup$
$begingroup$
@ ben, I realize now how walking will not cause the spacecraft to be continually accelerated due to a kinetic energy transfer. I am curious about one thing, and I asked the user 'Mark Foskey' the same question...if say the man was to ride on a segway instead of walking, would riding on powered wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
$begingroup$
no @HRIATEXP , except wheels are much less inefficient than walking, so the whole thing will be a lot smoother
$endgroup$
– JCRM
7 hours ago
add a comment |
$begingroup$
I think your confusion might be based around your contention that
he transferred a lot of kinetic energy to the spacecraft in those 20 minutes
Instead of considering the entire walk, consider each step. The astronaut is pushing against the "floor," and as he moves forward the spacecraft moves in the opposite direction such that momentum (in the spacecraft-astronaut system) is conserved. If he then stops, the station will stop as well. If he puts his opposite leg forward to take another step it is the same (momentum-wise) as if he stopped before taking another step. Prove this to yourself by considering a treadmill: as you walk the speed of the treadmill stays constant - it does not accelerate. Considering each step as a discrete action makes it more clear that he is not continually imparting more and more velocity to the spacecraft (remember, in the frame of the spacecraft he isn't accelerating once he begins walking at 3km/hr).
Maybe a simpler way to consider this that doesn't require kinesiology is the case in which the astronaut floats in the center at one end and pushes off with his legs towards the other end (left to right in your figure). The same forces are at play; he has essentially just imparted some velocity to the spacecraft in the opposite direction of his motion. If there were a hole at the right end of the figure he would shoot out into the void and the spacecraft would continue with the (relatively small) increased velocity. If we replace the jumping with a controlled explosion and the astronaut with exhaust, this is how rocket engines work. If we patch the hole and he hits the wall, he and the spacecraft will lose the velocity induced by the original jump and the system is as it was originally.
answered 16 hours ago
benben
391210
$endgroup$
$begingroup$
@ ben, I realize now how walking will not cause the spacecraft to be continually accelerated due to a kinetic energy transfer. I am curious about one thing, and I asked the user 'Mark Foskey' the same question...if say the man was to ride on a segway instead of walking, would riding on powered wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
$begingroup$
no @HRIATEXP , except wheels are much less inefficient than walking, so the whole thing will be a lot smoother
$endgroup$
– JCRM
7 hours ago
add a comment |
$begingroup$
I think your confusion might be based around your contention that
he transferred a lot of kinetic energy to the spacecraft in those 20 minutes
Instead of considering the entire walk, consider each step. The astronaut is pushing against the "floor," and as he moves forward the spacecraft moves in the opposite direction such that momentum (in the spacecraft-astronaut system) is conserved. If he then stops, the station will stop as well. If he puts his opposite leg forward to take another step it is the same (momentum-wise) as if he stopped before taking another step. Prove this to yourself by considering a treadmill: as you walk the speed of the treadmill stays constant - it does not accelerate. Considering each step as a discrete action makes it more clear that he is not continually imparting more and more velocity to the spacecraft (remember, in the frame of the spacecraft he isn't accelerating once he begins walking at 3km/hr).
Maybe a simpler way to consider this that doesn't require kinesiology is the case in which the astronaut floats in the center at one end and pushes off with his legs towards the other end (left to right in your figure). The same forces are at play; he has essentially just imparted some velocity to the spacecraft in the opposite direction of his motion. If there were a hole at the right end of the figure he would shoot out into the void and the spacecraft would continue with the (relatively small) increased velocity. If we replace the jumping with a controlled explosion and the astronaut with exhaust, this is how rocket engines work. If we patch the hole and he hits the wall, he and the spacecraft will lose the velocity induced by the original jump and the system is as it was originally.
answered 16 hours ago
benben
391210
$endgroup$
I think your confusion might be based around your contention that
he transferred a lot of kinetic energy to the spacecraft in those 20 minutes
Instead of considering the entire walk, consider each step. The astronaut is pushing against the "floor," and as he moves forward the spacecraft moves in the opposite direction such that momentum (in the spacecraft-astronaut system) is conserved. If he then stops, the station will stop as well. If he puts his opposite leg forward to take another step it is the same (momentum-wise) as if he stopped before taking another step. Prove this to yourself by considering a treadmill: as you walk the speed of the treadmill stays constant - it does not accelerate. Considering each step as a discrete action makes it more clear that he is not continually imparting more and more velocity to the spacecraft (remember, in the frame of the spacecraft he isn't accelerating once he begins walking at 3km/hr).
Maybe a simpler way to consider this that doesn't require kinesiology is the case in which the astronaut floats in the center at one end and pushes off with his legs towards the other end (left to right in your figure). The same forces are at play; he has essentially just imparted some velocity to the spacecraft in the opposite direction of his motion. If there were a hole at the right end of the figure he would shoot out into the void and the spacecraft would continue with the (relatively small) increased velocity. If we replace the jumping with a controlled explosion and the astronaut with exhaust, this is how rocket engines work. If we patch the hole and he hits the wall, he and the spacecraft will lose the velocity induced by the original jump and the system is as it was originally.
answered 16 hours ago
benben
391210
answered 16 hours ago
benben
391210
answered 16 hours ago
benben
391210
answered 16 hours ago
benben
391210
391210
$begingroup$
@ ben, I realize now how walking will not cause the spacecraft to be continually accelerated due to a kinetic energy transfer. I am curious about one thing, and I asked the user 'Mark Foskey' the same question...if say the man was to ride on a segway instead of walking, would riding on powered wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
$begingroup$
no @HRIATEXP , except wheels are much less inefficient than walking, so the whole thing will be a lot smoother
$endgroup$
– JCRM
7 hours ago
add a comment |
$begingroup$
@ ben, I realize now how walking will not cause the spacecraft to be continually accelerated due to a kinetic energy transfer. I am curious about one thing, and I asked the user 'Mark Foskey' the same question...if say the man was to ride on a segway instead of walking, would riding on powered wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
$begingroup$
no @HRIATEXP , except wheels are much less inefficient than walking, so the whole thing will be a lot smoother
$endgroup$
– JCRM
7 hours ago
$begingroup$
@ ben, I realize now how walking will not cause the spacecraft to be continually accelerated due to a kinetic energy transfer. I am curious about one thing, and I asked the user 'Mark Foskey' the same question...if say the man was to ride on a segway instead of walking, would riding on powered wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
$begingroup$
@ ben, I realize now how walking will not cause the spacecraft to be continually accelerated due to a kinetic energy transfer. I am curious about one thing, and I asked the user 'Mark Foskey' the same question...if say the man was to ride on a segway instead of walking, would riding on powered wheels make any difference?
$endgroup$
– HRIATEXP
14 hours ago
$begingroup$
no @HRIATEXP , except wheels are much less inefficient than walking, so the whole thing will be a lot smoother
$endgroup$
– JCRM
7 hours ago
$begingroup$
no @HRIATEXP , except wheels are much less inefficient than walking, so the whole thing will be a lot smoother
$endgroup$
– JCRM
7 hours ago
add a comment |
Thanks for contributing an answer to Space Exploration Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fspace.stackexchange.com%2fquestions%2f34590%2fwalking-in-a-rotating-spacecraft-and-newtons-3rd-law-of-motion%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
1
$begingroup$
The system isn't balanced, I wonder if it will start to wobble and precess as much as it will move laterally, causing the person to become nauseous and run back to the corner.
$endgroup$
– uhoh
yesterday
1
$begingroup$
@HRIATEXP ah, but which will rotate, the motor or the spacecraft??
$endgroup$
– Organic Marble
yesterday
1
$begingroup$
As the man takes his first step, the craft will begin to move in the opposite direction. As he takes each step the craft will continue to move. When he takes his last step, or crashes into the end will, both he and the craft will return to rest. Given the motor (And counterweight) is massive enough to spin the man and craft without issues, the amount it will move is slight.
$endgroup$
– JCRM
yesterday
1
$begingroup$
@OrganicMarble, that's a good point. I suppose that the spacecraft could be rotated with roll thrusters instead of an electric motor.
$endgroup$
– HRIATEXP
23 hours ago
1
$begingroup$
@uhoh, I can see that may happen, he may need to take Dramamine before he starts.
$endgroup$
– HRIATEXP
23 hours ago