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If gravity disappeared, would Newton's third law make everything that was pressed to the ground by gravity get pushed upwards?
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If gravity disappeared, would Newton's third law make everything that was pressed to the ground by gravity get pushed upwards?
newtonian-mechanics forces newtonian-gravity free-body-diagram planets
edited 16 mins ago
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634511
asked 13 hours ago
Casimir Rönnlöf
454
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up vote
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If gravity disappeared, would Newton's third law make everything that was pressed to the ground by gravity get pushed upwards?
newtonian-mechanics forces newtonian-gravity free-body-diagram planets
edited 16 mins ago
200_success
634511
asked 13 hours ago
Casimir Rönnlöf
454
3
Seems more of a Worldbuilding question than physics, to me.
– David Richerby
7 hours ago
It's relevant whether gravity vanishes suddenly, or over a time like an hour or day.
– Volker Siegel
4 hours ago
1
@DavidRicherby - The question would be great in Wordbuilding, but the goal and answer is different here. Here the goal is to understand Newton's third law. In wordbuilding we would account for a lot of interesting phenomena, like those outlined in the comments of my answer.
– Pere
2 hours ago
1
In fact, related questions have already been asked in Wordbuilding. worldbuilding.stackexchange.com/…
– Pere
2 hours ago
add a comment |Â
up vote
8
down vote
favorite
up vote
8
down vote
favorite
If gravity disappeared, would Newton's third law make everything that was pressed to the ground by gravity get pushed upwards?
newtonian-mechanics forces newtonian-gravity free-body-diagram planets
edited 16 mins ago
200_success
634511
asked 13 hours ago
Casimir Rönnlöf
454
If gravity disappeared, would Newton's third law make everything that was pressed to the ground by gravity get pushed upwards?
newtonian-mechanics forces newtonian-gravity free-body-diagram planets
newtonian-mechanics forces newtonian-gravity free-body-diagram planets
edited 16 mins ago
200_success
634511
asked 13 hours ago
Casimir Rönnlöf
454
edited 16 mins ago
200_success
634511
asked 13 hours ago
Casimir Rönnlöf
454
edited 16 mins ago
200_success
634511
edited 16 mins ago
200_success
634511
edited 16 mins ago
200_success
634511
634511
asked 13 hours ago
Casimir Rönnlöf
454
asked 13 hours ago
Casimir Rönnlöf
454
asked 13 hours ago
Casimir Rönnlöf
454
454
3
Seems more of a Worldbuilding question than physics, to me.
– David Richerby
7 hours ago
It's relevant whether gravity vanishes suddenly, or over a time like an hour or day.
– Volker Siegel
4 hours ago
1
@DavidRicherby - The question would be great in Wordbuilding, but the goal and answer is different here. Here the goal is to understand Newton's third law. In wordbuilding we would account for a lot of interesting phenomena, like those outlined in the comments of my answer.
– Pere
2 hours ago
1
In fact, related questions have already been asked in Wordbuilding. worldbuilding.stackexchange.com/…
– Pere
2 hours ago
add a comment |Â
3
Seems more of a Worldbuilding question than physics, to me.
– David Richerby
7 hours ago
It's relevant whether gravity vanishes suddenly, or over a time like an hour or day.
– Volker Siegel
4 hours ago
1
@DavidRicherby - The question would be great in Wordbuilding, but the goal and answer is different here. Here the goal is to understand Newton's third law. In wordbuilding we would account for a lot of interesting phenomena, like those outlined in the comments of my answer.
– Pere
2 hours ago
1
In fact, related questions have already been asked in Wordbuilding. worldbuilding.stackexchange.com/…
– Pere
2 hours ago
3
3
Seems more of a Worldbuilding question than physics, to me.
– David Richerby
7 hours ago
Seems more of a Worldbuilding question than physics, to me.
– David Richerby
7 hours ago
It's relevant whether gravity vanishes suddenly, or over a time like an hour or day.
– Volker Siegel
4 hours ago
It's relevant whether gravity vanishes suddenly, or over a time like an hour or day.
– Volker Siegel
4 hours ago
1
1
@DavidRicherby - The question would be great in Wordbuilding, but the goal and answer is different here. Here the goal is to understand Newton's third law. In wordbuilding we would account for a lot of interesting phenomena, like those outlined in the comments of my answer.
– Pere
2 hours ago
@DavidRicherby - The question would be great in Wordbuilding, but the goal and answer is different here. Here the goal is to understand Newton's third law. In wordbuilding we would account for a lot of interesting phenomena, like those outlined in the comments of my answer.
– Pere
2 hours ago
1
1
In fact, related questions have already been asked in Wordbuilding. worldbuilding.stackexchange.com/…
– Pere
2 hours ago
In fact, related questions have already been asked in Wordbuilding. worldbuilding.stackexchange.com/…
– Pere
2 hours ago
add a comment |Â
5 Answers
5
active
oldest
votes
up vote
23
down vote
accepted
As other answers explain, Newton's third law wouldn't push you upwards, because reaction disappears as soon of action (gravity) vanishes.
However, we need to keep in mind that we are siting on several thousand kilometres of rock heavily compressed by its own weight. If weight suddenly disappears, that rock will react like a spring and project itself and anything in the surface at very high speed to space. In fact, even the most conservative ballpark estimates of the elastic deformation of Earth in its present state are in the order of several kilometres, so that's the quite instant rebound we can expect.
answered 9 hours ago
Pere
66928
Not to mention that the earth is spinning, so everything would appear to fly upward as it continues along a path tangential to Earth's surface.
– Vaelus
3 hours ago
@Vaelus - Not to mention that the Earth itself is orbiting the Sun (which is, in turn orbiting the Galaxy's common centre). Minus gravity, everything would keep traveling in a straight line.
– Richard
3 hours ago
1
Yes, there would be a lot of interesting effects, like those produced by spinning. For example, without gravity hydrostatic pressure would vanish, the whole ocean would begin to boil and latent heat of vaporisation an adiabatic expansion of water vapour would cool and freeze most of the remaining water - while it flies away pushed by vapour expansion and seabed rebound - until all it get cooked away in a few days by the expansion of the Sun. However, I tried to keep the answer to the aspects related to reaction and Newton's third law.
– Pere
2 hours ago
add a comment |Â
up vote
12
down vote
Yes, but in almost all cases the push would be imperceptible.
Reaction forces from surfaces occur when the molecules in the wall are displaced from their equilibrium position. The harder they are pushed the more they are displaced, and the more they are displaced the harder they pushed back. When you stand on a surface without falling it is because you have displaced the surface enough for the reaction force to match your weight.
As an extreme example of this imagine standing on a trampoline. Heavier people make the trampoline surface sink lower than lighter people. The same is true on hard surfaces, but the displacement is basically imperceptible.
If you suddenly removed gravity, the reaction force from the displaced surface would still be there, and it would push you away until the equilibrium state of the surface is restored.
Again, imagine standing on a trampoline holding heavy weights. When you throw the weights away the trampoline will begin to push you up until you reach a new equilibrium. If the weights were heavy enough it could even launch you into the air.
The same thing would happen harder surfaces, but the amount of time the remaining reaction force would act on you would be tiny, and you would notices hardly any effect.
answered 11 hours ago
Luke Pritchett
2,257611
I'm trying to imagine holding weights on a trampoline, and throwing them off, to be launched into the air and I can't help but think it doesn't add up?
– djsmiley2k
4 hours ago
It would take very heavy weights to actually launch you off the trampoline, but even with light weights you would be moved upwards when you toss them away. Find a trampoline and do the experiment.
– Luke Pritchett
2 hours ago
add a comment |Â
up vote
6
down vote
No. The only reason a reaction force exists is because you are pushing down on the floor as a result of gravity pulling you down.
Perhaps one way to visualise this is to imagine a block on a slope at an angle $theta$ to the horizontal.
When $theta=0$ (i.e. the slope is flat), the block has force $mg$ down and so the reaction upwards is $R=mg$.
As $theta$ grows steadily, the downwards force is still $mg$, but now the reaction force (which is the force at a right angle to the slope) becomes $R=mgcostheta$.
Imagine this surface has very large friction, so that you can get quite a large $theta$ without the block slipping down. When you finally do reach a large enough $theta$, the block will slide down parallel to the slope. Note that if $R$ had retained its value of $mg$, the block would have by now accelerated away from the slope, which doesn't happen.
answered 13 hours ago
Garf
1,014117
1
Sorry, but this answer is just wrong because 1. this is the description of forces at equilibrium but suddenly eliminating gravity will not be an equilibrium state and 2. it completely ignores the underlying phenomenon as @Luke Pritchett points out. "Reaction" force is not one of the 4 fundamental forces, it's just a convenient rule of thumb for when the block has sunk enough into the material for the electric forces to counteract gravity. And it will bounce away a little when gravity disappears.
– csiz
9 hours ago
Ok, you are right, the "reaction force" is indeed a result of electrostatic interactions between the block and the floor. However, as Luke Pritchett also says, these forces are tiny, and are only significant because we're pushing down on them. If there were no gravity, there would be no pushing down on these molecules, and hence no reaction force. I believe my argument (at least for a simple classical point of view) is still valid.
– Garf
9 hours ago
2
The OP needs to qualify his question a bit. How fast does gravity disappear? If very slowly, the answer is probably no. If instantly, the answer is yes.
– David White
8 hours ago
add a comment |Â
up vote
4
down vote
You can simulate this experiment in real life with an electromagnet.
For instance, you can hold a vertically oriented steel plate by a horizontally oriented electromagnet, so that the plate is free to fall down, when the electromagnet is deenergized.
If the falling plate has a horizontal velocity component and describes a parabola, you can conclude that the normal force has pushed it. If the plate falls straight down, you can conclude that the there was no push.
Even without performing such experiment, you, probably, can predict that the plate will fall straight down. This is because the normal force is a reaction force and it never exceeds the applied force causing it, be that electromagnet attraction or gravity. So, as the applied force disappears, gradually or suddenly, the normal force will disappear with it and, therefore, there won't be any push.
answered 13 hours ago
V.F.
9,93021024
add a comment |Â
up vote
0
down vote
In the absence of gravity.nothing gets pushed up because there is No force pushing it.every fixed object will remain fixed and all the other tend to be floating because nothing pulls it down .
answered 6 hours ago
user211277
32
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5 Answers
5
active
oldest
votes
5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
23
down vote
accepted
As other answers explain, Newton's third law wouldn't push you upwards, because reaction disappears as soon of action (gravity) vanishes.
However, we need to keep in mind that we are siting on several thousand kilometres of rock heavily compressed by its own weight. If weight suddenly disappears, that rock will react like a spring and project itself and anything in the surface at very high speed to space. In fact, even the most conservative ballpark estimates of the elastic deformation of Earth in its present state are in the order of several kilometres, so that's the quite instant rebound we can expect.
answered 9 hours ago
Pere
66928
Not to mention that the earth is spinning, so everything would appear to fly upward as it continues along a path tangential to Earth's surface.
– Vaelus
3 hours ago
@Vaelus - Not to mention that the Earth itself is orbiting the Sun (which is, in turn orbiting the Galaxy's common centre). Minus gravity, everything would keep traveling in a straight line.
– Richard
3 hours ago
1
Yes, there would be a lot of interesting effects, like those produced by spinning. For example, without gravity hydrostatic pressure would vanish, the whole ocean would begin to boil and latent heat of vaporisation an adiabatic expansion of water vapour would cool and freeze most of the remaining water - while it flies away pushed by vapour expansion and seabed rebound - until all it get cooked away in a few days by the expansion of the Sun. However, I tried to keep the answer to the aspects related to reaction and Newton's third law.
– Pere
2 hours ago
add a comment |Â
up vote
23
down vote
accepted
As other answers explain, Newton's third law wouldn't push you upwards, because reaction disappears as soon of action (gravity) vanishes.
However, we need to keep in mind that we are siting on several thousand kilometres of rock heavily compressed by its own weight. If weight suddenly disappears, that rock will react like a spring and project itself and anything in the surface at very high speed to space. In fact, even the most conservative ballpark estimates of the elastic deformation of Earth in its present state are in the order of several kilometres, so that's the quite instant rebound we can expect.
answered 9 hours ago
Pere
66928
Not to mention that the earth is spinning, so everything would appear to fly upward as it continues along a path tangential to Earth's surface.
– Vaelus
3 hours ago
@Vaelus - Not to mention that the Earth itself is orbiting the Sun (which is, in turn orbiting the Galaxy's common centre). Minus gravity, everything would keep traveling in a straight line.
– Richard
3 hours ago
1
Yes, there would be a lot of interesting effects, like those produced by spinning. For example, without gravity hydrostatic pressure would vanish, the whole ocean would begin to boil and latent heat of vaporisation an adiabatic expansion of water vapour would cool and freeze most of the remaining water - while it flies away pushed by vapour expansion and seabed rebound - until all it get cooked away in a few days by the expansion of the Sun. However, I tried to keep the answer to the aspects related to reaction and Newton's third law.
– Pere
2 hours ago
add a comment |Â
up vote
23
down vote
accepted
up vote
23
down vote
accepted
As other answers explain, Newton's third law wouldn't push you upwards, because reaction disappears as soon of action (gravity) vanishes.
However, we need to keep in mind that we are siting on several thousand kilometres of rock heavily compressed by its own weight. If weight suddenly disappears, that rock will react like a spring and project itself and anything in the surface at very high speed to space. In fact, even the most conservative ballpark estimates of the elastic deformation of Earth in its present state are in the order of several kilometres, so that's the quite instant rebound we can expect.
answered 9 hours ago
Pere
66928
As other answers explain, Newton's third law wouldn't push you upwards, because reaction disappears as soon of action (gravity) vanishes.
However, we need to keep in mind that we are siting on several thousand kilometres of rock heavily compressed by its own weight. If weight suddenly disappears, that rock will react like a spring and project itself and anything in the surface at very high speed to space. In fact, even the most conservative ballpark estimates of the elastic deformation of Earth in its present state are in the order of several kilometres, so that's the quite instant rebound we can expect.
answered 9 hours ago
Pere
66928
edited 5 hours ago
answered 9 hours ago
Pere
66928
answered 9 hours ago
Pere
66928
answered 9 hours ago
Pere
66928
66928
Not to mention that the earth is spinning, so everything would appear to fly upward as it continues along a path tangential to Earth's surface.
– Vaelus
3 hours ago
@Vaelus - Not to mention that the Earth itself is orbiting the Sun (which is, in turn orbiting the Galaxy's common centre). Minus gravity, everything would keep traveling in a straight line.
– Richard
3 hours ago
1
Yes, there would be a lot of interesting effects, like those produced by spinning. For example, without gravity hydrostatic pressure would vanish, the whole ocean would begin to boil and latent heat of vaporisation an adiabatic expansion of water vapour would cool and freeze most of the remaining water - while it flies away pushed by vapour expansion and seabed rebound - until all it get cooked away in a few days by the expansion of the Sun. However, I tried to keep the answer to the aspects related to reaction and Newton's third law.
– Pere
2 hours ago
add a comment |Â
Not to mention that the earth is spinning, so everything would appear to fly upward as it continues along a path tangential to Earth's surface.
– Vaelus
3 hours ago
@Vaelus - Not to mention that the Earth itself is orbiting the Sun (which is, in turn orbiting the Galaxy's common centre). Minus gravity, everything would keep traveling in a straight line.
– Richard
3 hours ago
1
Yes, there would be a lot of interesting effects, like those produced by spinning. For example, without gravity hydrostatic pressure would vanish, the whole ocean would begin to boil and latent heat of vaporisation an adiabatic expansion of water vapour would cool and freeze most of the remaining water - while it flies away pushed by vapour expansion and seabed rebound - until all it get cooked away in a few days by the expansion of the Sun. However, I tried to keep the answer to the aspects related to reaction and Newton's third law.
– Pere
2 hours ago
Not to mention that the earth is spinning, so everything would appear to fly upward as it continues along a path tangential to Earth's surface.
– Vaelus
3 hours ago
Not to mention that the earth is spinning, so everything would appear to fly upward as it continues along a path tangential to Earth's surface.
– Vaelus
3 hours ago
@Vaelus - Not to mention that the Earth itself is orbiting the Sun (which is, in turn orbiting the Galaxy's common centre). Minus gravity, everything would keep traveling in a straight line.
– Richard
3 hours ago
@Vaelus - Not to mention that the Earth itself is orbiting the Sun (which is, in turn orbiting the Galaxy's common centre). Minus gravity, everything would keep traveling in a straight line.
– Richard
3 hours ago
1
1
Yes, there would be a lot of interesting effects, like those produced by spinning. For example, without gravity hydrostatic pressure would vanish, the whole ocean would begin to boil and latent heat of vaporisation an adiabatic expansion of water vapour would cool and freeze most of the remaining water - while it flies away pushed by vapour expansion and seabed rebound - until all it get cooked away in a few days by the expansion of the Sun. However, I tried to keep the answer to the aspects related to reaction and Newton's third law.
– Pere
2 hours ago
Yes, there would be a lot of interesting effects, like those produced by spinning. For example, without gravity hydrostatic pressure would vanish, the whole ocean would begin to boil and latent heat of vaporisation an adiabatic expansion of water vapour would cool and freeze most of the remaining water - while it flies away pushed by vapour expansion and seabed rebound - until all it get cooked away in a few days by the expansion of the Sun. However, I tried to keep the answer to the aspects related to reaction and Newton's third law.
– Pere
2 hours ago
add a comment |Â
up vote
12
down vote
Yes, but in almost all cases the push would be imperceptible.
Reaction forces from surfaces occur when the molecules in the wall are displaced from their equilibrium position. The harder they are pushed the more they are displaced, and the more they are displaced the harder they pushed back. When you stand on a surface without falling it is because you have displaced the surface enough for the reaction force to match your weight.
As an extreme example of this imagine standing on a trampoline. Heavier people make the trampoline surface sink lower than lighter people. The same is true on hard surfaces, but the displacement is basically imperceptible.
If you suddenly removed gravity, the reaction force from the displaced surface would still be there, and it would push you away until the equilibrium state of the surface is restored.
Again, imagine standing on a trampoline holding heavy weights. When you throw the weights away the trampoline will begin to push you up until you reach a new equilibrium. If the weights were heavy enough it could even launch you into the air.
The same thing would happen harder surfaces, but the amount of time the remaining reaction force would act on you would be tiny, and you would notices hardly any effect.
answered 11 hours ago
Luke Pritchett
2,257611
I'm trying to imagine holding weights on a trampoline, and throwing them off, to be launched into the air and I can't help but think it doesn't add up?
– djsmiley2k
4 hours ago
It would take very heavy weights to actually launch you off the trampoline, but even with light weights you would be moved upwards when you toss them away. Find a trampoline and do the experiment.
– Luke Pritchett
2 hours ago
add a comment |Â
up vote
12
down vote
Yes, but in almost all cases the push would be imperceptible.
Reaction forces from surfaces occur when the molecules in the wall are displaced from their equilibrium position. The harder they are pushed the more they are displaced, and the more they are displaced the harder they pushed back. When you stand on a surface without falling it is because you have displaced the surface enough for the reaction force to match your weight.
As an extreme example of this imagine standing on a trampoline. Heavier people make the trampoline surface sink lower than lighter people. The same is true on hard surfaces, but the displacement is basically imperceptible.
If you suddenly removed gravity, the reaction force from the displaced surface would still be there, and it would push you away until the equilibrium state of the surface is restored.
Again, imagine standing on a trampoline holding heavy weights. When you throw the weights away the trampoline will begin to push you up until you reach a new equilibrium. If the weights were heavy enough it could even launch you into the air.
The same thing would happen harder surfaces, but the amount of time the remaining reaction force would act on you would be tiny, and you would notices hardly any effect.
answered 11 hours ago
Luke Pritchett
2,257611
I'm trying to imagine holding weights on a trampoline, and throwing them off, to be launched into the air and I can't help but think it doesn't add up?
– djsmiley2k
4 hours ago
It would take very heavy weights to actually launch you off the trampoline, but even with light weights you would be moved upwards when you toss them away. Find a trampoline and do the experiment.
– Luke Pritchett
2 hours ago
add a comment |Â
up vote
12
down vote
up vote
12
down vote
Yes, but in almost all cases the push would be imperceptible.
Reaction forces from surfaces occur when the molecules in the wall are displaced from their equilibrium position. The harder they are pushed the more they are displaced, and the more they are displaced the harder they pushed back. When you stand on a surface without falling it is because you have displaced the surface enough for the reaction force to match your weight.
As an extreme example of this imagine standing on a trampoline. Heavier people make the trampoline surface sink lower than lighter people. The same is true on hard surfaces, but the displacement is basically imperceptible.
If you suddenly removed gravity, the reaction force from the displaced surface would still be there, and it would push you away until the equilibrium state of the surface is restored.
Again, imagine standing on a trampoline holding heavy weights. When you throw the weights away the trampoline will begin to push you up until you reach a new equilibrium. If the weights were heavy enough it could even launch you into the air.
The same thing would happen harder surfaces, but the amount of time the remaining reaction force would act on you would be tiny, and you would notices hardly any effect.
answered 11 hours ago
Luke Pritchett
2,257611
Yes, but in almost all cases the push would be imperceptible.
Reaction forces from surfaces occur when the molecules in the wall are displaced from their equilibrium position. The harder they are pushed the more they are displaced, and the more they are displaced the harder they pushed back. When you stand on a surface without falling it is because you have displaced the surface enough for the reaction force to match your weight.
As an extreme example of this imagine standing on a trampoline. Heavier people make the trampoline surface sink lower than lighter people. The same is true on hard surfaces, but the displacement is basically imperceptible.
If you suddenly removed gravity, the reaction force from the displaced surface would still be there, and it would push you away until the equilibrium state of the surface is restored.
Again, imagine standing on a trampoline holding heavy weights. When you throw the weights away the trampoline will begin to push you up until you reach a new equilibrium. If the weights were heavy enough it could even launch you into the air.
The same thing would happen harder surfaces, but the amount of time the remaining reaction force would act on you would be tiny, and you would notices hardly any effect.
answered 11 hours ago
Luke Pritchett
2,257611
answered 11 hours ago
Luke Pritchett
2,257611
answered 11 hours ago
Luke Pritchett
2,257611
answered 11 hours ago
Luke Pritchett
2,257611
2,257611
I'm trying to imagine holding weights on a trampoline, and throwing them off, to be launched into the air and I can't help but think it doesn't add up?
– djsmiley2k
4 hours ago
It would take very heavy weights to actually launch you off the trampoline, but even with light weights you would be moved upwards when you toss them away. Find a trampoline and do the experiment.
– Luke Pritchett
2 hours ago
add a comment |Â
I'm trying to imagine holding weights on a trampoline, and throwing them off, to be launched into the air and I can't help but think it doesn't add up?
– djsmiley2k
4 hours ago
It would take very heavy weights to actually launch you off the trampoline, but even with light weights you would be moved upwards when you toss them away. Find a trampoline and do the experiment.
– Luke Pritchett
2 hours ago
I'm trying to imagine holding weights on a trampoline, and throwing them off, to be launched into the air and I can't help but think it doesn't add up?
– djsmiley2k
4 hours ago
I'm trying to imagine holding weights on a trampoline, and throwing them off, to be launched into the air and I can't help but think it doesn't add up?
– djsmiley2k
4 hours ago
It would take very heavy weights to actually launch you off the trampoline, but even with light weights you would be moved upwards when you toss them away. Find a trampoline and do the experiment.
– Luke Pritchett
2 hours ago
It would take very heavy weights to actually launch you off the trampoline, but even with light weights you would be moved upwards when you toss them away. Find a trampoline and do the experiment.
– Luke Pritchett
2 hours ago
add a comment |Â
up vote
6
down vote
No. The only reason a reaction force exists is because you are pushing down on the floor as a result of gravity pulling you down.
Perhaps one way to visualise this is to imagine a block on a slope at an angle $theta$ to the horizontal.
When $theta=0$ (i.e. the slope is flat), the block has force $mg$ down and so the reaction upwards is $R=mg$.
As $theta$ grows steadily, the downwards force is still $mg$, but now the reaction force (which is the force at a right angle to the slope) becomes $R=mgcostheta$.
Imagine this surface has very large friction, so that you can get quite a large $theta$ without the block slipping down. When you finally do reach a large enough $theta$, the block will slide down parallel to the slope. Note that if $R$ had retained its value of $mg$, the block would have by now accelerated away from the slope, which doesn't happen.
answered 13 hours ago
Garf
1,014117
1
Sorry, but this answer is just wrong because 1. this is the description of forces at equilibrium but suddenly eliminating gravity will not be an equilibrium state and 2. it completely ignores the underlying phenomenon as @Luke Pritchett points out. "Reaction" force is not one of the 4 fundamental forces, it's just a convenient rule of thumb for when the block has sunk enough into the material for the electric forces to counteract gravity. And it will bounce away a little when gravity disappears.
– csiz
9 hours ago
Ok, you are right, the "reaction force" is indeed a result of electrostatic interactions between the block and the floor. However, as Luke Pritchett also says, these forces are tiny, and are only significant because we're pushing down on them. If there were no gravity, there would be no pushing down on these molecules, and hence no reaction force. I believe my argument (at least for a simple classical point of view) is still valid.
– Garf
9 hours ago
2
The OP needs to qualify his question a bit. How fast does gravity disappear? If very slowly, the answer is probably no. If instantly, the answer is yes.
– David White
8 hours ago
add a comment |Â
up vote
6
down vote
No. The only reason a reaction force exists is because you are pushing down on the floor as a result of gravity pulling you down.
Perhaps one way to visualise this is to imagine a block on a slope at an angle $theta$ to the horizontal.
When $theta=0$ (i.e. the slope is flat), the block has force $mg$ down and so the reaction upwards is $R=mg$.
As $theta$ grows steadily, the downwards force is still $mg$, but now the reaction force (which is the force at a right angle to the slope) becomes $R=mgcostheta$.
Imagine this surface has very large friction, so that you can get quite a large $theta$ without the block slipping down. When you finally do reach a large enough $theta$, the block will slide down parallel to the slope. Note that if $R$ had retained its value of $mg$, the block would have by now accelerated away from the slope, which doesn't happen.
answered 13 hours ago
Garf
1,014117
1
Sorry, but this answer is just wrong because 1. this is the description of forces at equilibrium but suddenly eliminating gravity will not be an equilibrium state and 2. it completely ignores the underlying phenomenon as @Luke Pritchett points out. "Reaction" force is not one of the 4 fundamental forces, it's just a convenient rule of thumb for when the block has sunk enough into the material for the electric forces to counteract gravity. And it will bounce away a little when gravity disappears.
– csiz
9 hours ago
Ok, you are right, the "reaction force" is indeed a result of electrostatic interactions between the block and the floor. However, as Luke Pritchett also says, these forces are tiny, and are only significant because we're pushing down on them. If there were no gravity, there would be no pushing down on these molecules, and hence no reaction force. I believe my argument (at least for a simple classical point of view) is still valid.
– Garf
9 hours ago
2
The OP needs to qualify his question a bit. How fast does gravity disappear? If very slowly, the answer is probably no. If instantly, the answer is yes.
– David White
8 hours ago
add a comment |Â
up vote
6
down vote
up vote
6
down vote
No. The only reason a reaction force exists is because you are pushing down on the floor as a result of gravity pulling you down.
Perhaps one way to visualise this is to imagine a block on a slope at an angle $theta$ to the horizontal.
When $theta=0$ (i.e. the slope is flat), the block has force $mg$ down and so the reaction upwards is $R=mg$.
As $theta$ grows steadily, the downwards force is still $mg$, but now the reaction force (which is the force at a right angle to the slope) becomes $R=mgcostheta$.
Imagine this surface has very large friction, so that you can get quite a large $theta$ without the block slipping down. When you finally do reach a large enough $theta$, the block will slide down parallel to the slope. Note that if $R$ had retained its value of $mg$, the block would have by now accelerated away from the slope, which doesn't happen.
answered 13 hours ago
Garf
1,014117
No. The only reason a reaction force exists is because you are pushing down on the floor as a result of gravity pulling you down.
Perhaps one way to visualise this is to imagine a block on a slope at an angle $theta$ to the horizontal.
When $theta=0$ (i.e. the slope is flat), the block has force $mg$ down and so the reaction upwards is $R=mg$.
As $theta$ grows steadily, the downwards force is still $mg$, but now the reaction force (which is the force at a right angle to the slope) becomes $R=mgcostheta$.
Imagine this surface has very large friction, so that you can get quite a large $theta$ without the block slipping down. When you finally do reach a large enough $theta$, the block will slide down parallel to the slope. Note that if $R$ had retained its value of $mg$, the block would have by now accelerated away from the slope, which doesn't happen.
answered 13 hours ago
Garf
1,014117
answered 13 hours ago
Garf
1,014117
answered 13 hours ago
Garf
1,014117
answered 13 hours ago
Garf
1,014117
1,014117
1
Sorry, but this answer is just wrong because 1. this is the description of forces at equilibrium but suddenly eliminating gravity will not be an equilibrium state and 2. it completely ignores the underlying phenomenon as @Luke Pritchett points out. "Reaction" force is not one of the 4 fundamental forces, it's just a convenient rule of thumb for when the block has sunk enough into the material for the electric forces to counteract gravity. And it will bounce away a little when gravity disappears.
– csiz
9 hours ago
Ok, you are right, the "reaction force" is indeed a result of electrostatic interactions between the block and the floor. However, as Luke Pritchett also says, these forces are tiny, and are only significant because we're pushing down on them. If there were no gravity, there would be no pushing down on these molecules, and hence no reaction force. I believe my argument (at least for a simple classical point of view) is still valid.
– Garf
9 hours ago
2
The OP needs to qualify his question a bit. How fast does gravity disappear? If very slowly, the answer is probably no. If instantly, the answer is yes.
– David White
8 hours ago
add a comment |Â
1
Sorry, but this answer is just wrong because 1. this is the description of forces at equilibrium but suddenly eliminating gravity will not be an equilibrium state and 2. it completely ignores the underlying phenomenon as @Luke Pritchett points out. "Reaction" force is not one of the 4 fundamental forces, it's just a convenient rule of thumb for when the block has sunk enough into the material for the electric forces to counteract gravity. And it will bounce away a little when gravity disappears.
– csiz
9 hours ago
Ok, you are right, the "reaction force" is indeed a result of electrostatic interactions between the block and the floor. However, as Luke Pritchett also says, these forces are tiny, and are only significant because we're pushing down on them. If there were no gravity, there would be no pushing down on these molecules, and hence no reaction force. I believe my argument (at least for a simple classical point of view) is still valid.
– Garf
9 hours ago
2
The OP needs to qualify his question a bit. How fast does gravity disappear? If very slowly, the answer is probably no. If instantly, the answer is yes.
– David White
8 hours ago
1
1
Sorry, but this answer is just wrong because 1. this is the description of forces at equilibrium but suddenly eliminating gravity will not be an equilibrium state and 2. it completely ignores the underlying phenomenon as @Luke Pritchett points out. "Reaction" force is not one of the 4 fundamental forces, it's just a convenient rule of thumb for when the block has sunk enough into the material for the electric forces to counteract gravity. And it will bounce away a little when gravity disappears.
– csiz
9 hours ago
Sorry, but this answer is just wrong because 1. this is the description of forces at equilibrium but suddenly eliminating gravity will not be an equilibrium state and 2. it completely ignores the underlying phenomenon as @Luke Pritchett points out. "Reaction" force is not one of the 4 fundamental forces, it's just a convenient rule of thumb for when the block has sunk enough into the material for the electric forces to counteract gravity. And it will bounce away a little when gravity disappears.
– csiz
9 hours ago
Ok, you are right, the "reaction force" is indeed a result of electrostatic interactions between the block and the floor. However, as Luke Pritchett also says, these forces are tiny, and are only significant because we're pushing down on them. If there were no gravity, there would be no pushing down on these molecules, and hence no reaction force. I believe my argument (at least for a simple classical point of view) is still valid.
– Garf
9 hours ago
Ok, you are right, the "reaction force" is indeed a result of electrostatic interactions between the block and the floor. However, as Luke Pritchett also says, these forces are tiny, and are only significant because we're pushing down on them. If there were no gravity, there would be no pushing down on these molecules, and hence no reaction force. I believe my argument (at least for a simple classical point of view) is still valid.
– Garf
9 hours ago
2
2
The OP needs to qualify his question a bit. How fast does gravity disappear? If very slowly, the answer is probably no. If instantly, the answer is yes.
– David White
8 hours ago
The OP needs to qualify his question a bit. How fast does gravity disappear? If very slowly, the answer is probably no. If instantly, the answer is yes.
– David White
8 hours ago
add a comment |Â
up vote
4
down vote
You can simulate this experiment in real life with an electromagnet.
For instance, you can hold a vertically oriented steel plate by a horizontally oriented electromagnet, so that the plate is free to fall down, when the electromagnet is deenergized.
If the falling plate has a horizontal velocity component and describes a parabola, you can conclude that the normal force has pushed it. If the plate falls straight down, you can conclude that the there was no push.
Even without performing such experiment, you, probably, can predict that the plate will fall straight down. This is because the normal force is a reaction force and it never exceeds the applied force causing it, be that electromagnet attraction or gravity. So, as the applied force disappears, gradually or suddenly, the normal force will disappear with it and, therefore, there won't be any push.
answered 13 hours ago
V.F.
9,93021024
add a comment |Â
up vote
4
down vote
You can simulate this experiment in real life with an electromagnet.
For instance, you can hold a vertically oriented steel plate by a horizontally oriented electromagnet, so that the plate is free to fall down, when the electromagnet is deenergized.
If the falling plate has a horizontal velocity component and describes a parabola, you can conclude that the normal force has pushed it. If the plate falls straight down, you can conclude that the there was no push.
Even without performing such experiment, you, probably, can predict that the plate will fall straight down. This is because the normal force is a reaction force and it never exceeds the applied force causing it, be that electromagnet attraction or gravity. So, as the applied force disappears, gradually or suddenly, the normal force will disappear with it and, therefore, there won't be any push.
answered 13 hours ago
V.F.
9,93021024
add a comment |Â
up vote
4
down vote
up vote
4
down vote
You can simulate this experiment in real life with an electromagnet.
For instance, you can hold a vertically oriented steel plate by a horizontally oriented electromagnet, so that the plate is free to fall down, when the electromagnet is deenergized.
If the falling plate has a horizontal velocity component and describes a parabola, you can conclude that the normal force has pushed it. If the plate falls straight down, you can conclude that the there was no push.
Even without performing such experiment, you, probably, can predict that the plate will fall straight down. This is because the normal force is a reaction force and it never exceeds the applied force causing it, be that electromagnet attraction or gravity. So, as the applied force disappears, gradually or suddenly, the normal force will disappear with it and, therefore, there won't be any push.
answered 13 hours ago
V.F.
9,93021024
You can simulate this experiment in real life with an electromagnet.
For instance, you can hold a vertically oriented steel plate by a horizontally oriented electromagnet, so that the plate is free to fall down, when the electromagnet is deenergized.
If the falling plate has a horizontal velocity component and describes a parabola, you can conclude that the normal force has pushed it. If the plate falls straight down, you can conclude that the there was no push.
Even without performing such experiment, you, probably, can predict that the plate will fall straight down. This is because the normal force is a reaction force and it never exceeds the applied force causing it, be that electromagnet attraction or gravity. So, as the applied force disappears, gradually or suddenly, the normal force will disappear with it and, therefore, there won't be any push.
answered 13 hours ago
V.F.
9,93021024
answered 13 hours ago
V.F.
9,93021024
answered 13 hours ago
V.F.
9,93021024
answered 13 hours ago
V.F.
9,93021024
9,93021024
add a comment |Â
add a comment |Â
up vote
0
down vote
In the absence of gravity.nothing gets pushed up because there is No force pushing it.every fixed object will remain fixed and all the other tend to be floating because nothing pulls it down .
answered 6 hours ago
user211277
32
New contributor
user211277 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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add a comment |Â
up vote
0
down vote
In the absence of gravity.nothing gets pushed up because there is No force pushing it.every fixed object will remain fixed and all the other tend to be floating because nothing pulls it down .
answered 6 hours ago
user211277
32
New contributor
user211277 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |Â
up vote
0
down vote
up vote
0
down vote
In the absence of gravity.nothing gets pushed up because there is No force pushing it.every fixed object will remain fixed and all the other tend to be floating because nothing pulls it down .
answered 6 hours ago
user211277
32
New contributor
user211277 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
In the absence of gravity.nothing gets pushed up because there is No force pushing it.every fixed object will remain fixed and all the other tend to be floating because nothing pulls it down .
answered 6 hours ago
user211277
32
New contributor
user211277 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 6 hours ago
user211277
32
New contributor
user211277 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 6 hours ago
user211277
32
answered 6 hours ago
user211277
32
32
New contributor
user211277 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
user211277 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
user211277 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |Â
add a comment |Â
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3
Seems more of a Worldbuilding question than physics, to me.
– David Richerby
7 hours ago
It's relevant whether gravity vanishes suddenly, or over a time like an hour or day.
– Volker Siegel
4 hours ago
1
@DavidRicherby - The question would be great in Wordbuilding, but the goal and answer is different here. Here the goal is to understand Newton's third law. In wordbuilding we would account for a lot of interesting phenomena, like those outlined in the comments of my answer.
– Pere
2 hours ago
1
In fact, related questions have already been asked in Wordbuilding. worldbuilding.stackexchange.com/…
– Pere
2 hours ago