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If earth was all land, and everyone started running west...

Originally posted by: Kelvrick
Why would they be. Us running west doesn't effect the time it takes the earth to rotate.
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I think he is saying that if everyone ran west, we would be pushing the earth east with our feet and thus speeding up the earths rotation.

That won't happen BTW.
 
Originally posted by: swtethan
iirc... earth rotates at 1000 mph at the equator
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That's why long distance jumpers try to stay in the air so long, because the longer they are in the air, the further the Earth rotates.
 
assuming the humans were evenly dispersed about the equator (location at which their collective mass would have the largest impact on the earths angular speed), the moment of inertia for the two bodies are shown below:

moment of inertia of earth = (2/5)*m*r^2 = 9.77x10^37 kg*m^2
moment of inertia of humans = sum(m*r^2) = 1.85x10^25 kg*m^2

the moment of inertia of the earth is 12 orders of magnitude higher than that of the humans, so it is safe to say that they would have little to no effect on the speed of the earth.
 
Originally posted by: ucdbiendog
assuming the humans were evenly dispersed about the equator (location at which their collective mass would have the largest impact on the earths angular speed), the moment of inertia for the two bodies are shown below:

moment of inertia of earth = (2/5)*m*r^2 = 9.77x10^37 kg*m^2
moment of inertia of humans = sum(m*r^2) = 1.85x10^25 kg*m^2

the moment of inertia of the earth is 12 orders of magnitude higher than that of the humans, so it is safe to say that they would have little to no effect on the speed of the earth.
Click to expand...

Doing those calculations you must no that there's no such thing as "no effect". The day would get shorter but we'd be hard pressed to measure it.
 
Originally posted by: Forsythe
Originally posted by: ucdbiendog
assuming the humans were evenly dispersed about the equator (location at which their collective mass would have the largest impact on the earths angular speed), the moment of inertia for the two bodies are shown below:

moment of inertia of earth = (2/5)*m*r^2 = 9.77x10^37 kg*m^2
moment of inertia of humans = sum(m*r^2) = 1.85x10^25 kg*m^2

the moment of inertia of the earth is 12 orders of magnitude higher than that of the humans, so it is safe to say that they would have little to no effect on the speed of the earth.
Click to expand...

Doing those calculations you must no that there's no such thing as "no effect". The day would get shorter but we'd be hard pressed to measure it.
Click to expand...

s/no effect/no significant effect/

The concept of significant figures was implied. Remember significant figures?
 
Originally posted by: bersl2
Originally posted by: Forsythe
Originally posted by: ucdbiendog
assuming the humans were evenly dispersed about the equator (location at which their collective mass would have the largest impact on the earths angular speed), the moment of inertia for the two bodies are shown below:

moment of inertia of earth = (2/5)*m*r^2 = 9.77x10^37 kg*m^2
moment of inertia of humans = sum(m*r^2) = 1.85x10^25 kg*m^2

the moment of inertia of the earth is 12 orders of magnitude higher than that of the humans, so it is safe to say that they would have little to no effect on the speed of the earth.
Click to expand...

Doing those calculations you must no that there's no such thing as "no effect". The day would get shorter but we'd be hard pressed to measure it.
Click to expand...

s/no effect/no significant effect/

The concept of significant figures was implied. Remember significant figures?
Click to expand...

I don't care about significant numbers, when i do my uni physics, i use as many numbers as i can get hold of 😛

He asked if the day would get shorter, and yes it would. Not by much, but if we ran for some time it would show.
 
Technically if everyone was running the same direction, it would have an affect on the earth's rotational speed. As you push off from the ground, you are pushing yourself one way and the ground the other way. Pushing the ground doesn't actually move it but if 5 billion people were all doing that at the same time, I'm sure it would have some effect.
 
Originally posted by: FrankyJunior
Technically if everyone was running the same direction, it would have an affect on the earth's rotational speed. As you push off from the ground, you are pushing yourself one way and the ground the other way. Pushing the ground doesn't actually move it but if 5 billion people were all doing that at the same time, I'm sure it would have some effect.
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A single person accelerating to walking speed does change the rotation of the earth... it's just not measureable.
 
Originally posted by: mercanucaribe
Originally posted by: FrankyJunior
Technically if everyone was running the same direction, it would have an affect on the earth's rotational speed. As you push off from the ground, you are pushing yourself one way and the ground the other way. Pushing the ground doesn't actually move it but if 5 billion people were all doing that at the same time, I'm sure it would have some effect.
Click to expand...

A single person accelerating to walking speed does change the rotation of the earth... it's just not measureable.
Click to expand...

Yeah I know but with everyone in the world walking different directions all day, most of it just cancels out with each other.
 
Originally posted by: Forsythe
Originally posted by: bersl2
Originally posted by: Forsythe
Originally posted by: ucdbiendog
assuming the humans were evenly dispersed about the equator (location at which their collective mass would have the largest impact on the earths angular speed), the moment of inertia for the two bodies are shown below:

moment of inertia of earth = (2/5)*m*r^2 = 9.77x10^37 kg*m^2
moment of inertia of humans = sum(m*r^2) = 1.85x10^25 kg*m^2

the moment of inertia of the earth is 12 orders of magnitude higher than that of the humans, so it is safe to say that they would have little to no effect on the speed of the earth.
Click to expand...

Doing those calculations you must no that there's no such thing as "no effect". The day would get shorter but we'd be hard pressed to measure it.
Click to expand...

s/no effect/no significant effect/

The concept of significant figures was implied. Remember significant figures?
Click to expand...

I don't care about significant numbers, when i do my uni physics, i use as many numbers as i can get hold of 😛

He asked if the day would get shorter, and yes it would. Not by much, but if we ran for some time it would show.
Click to expand...

as long as the humans are running at constant speed, there is no change in the rotational speed of the earth, no matter how long they have been running for. it is only when the people go from standing to running will the speed change (basically the rotational momentum of the system has to stay the same, so when the peoples momentum changes, the earths must change equally and oppositely). That and the change would be so small it would be unnoticeable. what uni do you go to where they dont care about sig figs?

edit: sorry for nested quote, please dont ban
 
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