Help me understand how it is that the Earth spins

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Hashi
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Help me understand how it is that the Earth spins

Post by Hashi »

Ok so another random topic

How is it that we don't notice the Earth spinning beneath us? I know it spins very fast, but surely we're all moving with the Earth too, it can't spin under our feet but for us to remain still. Or does "still" have a different definition in this case?

If I took an ant and put it on an equivalent sized rock out in space and spun it, you would see the ant spin around with the sphere.

So yeah how does it work out that we dont feel the spin of the Earth beneath us?

Thank you in advance friends
bobby 55
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Re: Help me understand how it is that the Earth spins

Post by bobby 55 »

Yeah, the fact that we are spinning at the same rate as the Earth makes it seem things are stationary. That's how things like communication satellites maintain a stationary orbit over a specific country. They're orbiting as fast as the Earth is spinning. If I remember my science lessons, from a thousand years ago, the spinning thing started when the planets were gas and stuff before they were formed. It's something to do with ease of motion or the like. Once again DDL will probably have the correct answer if he's not too busy laughing his guts out mine. :D
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ggrotz
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Re: Help me understand how it is that the Earth spins

Post by ggrotz »

Hashi wrote: So yeah how does it work out that we dont feel the spin of the Earth beneath us?
Bobby gave you a good answer. The reason is we are moving the same speed as the earth since gravity holds us down. We don't feel it because we only feel changes in force vectors and not the forces themselves. This is also the reason we don't feel the effects of gravity unless we jump or fall from a higher place.

If you need a smaller scale example, when you take a ride in an automobile you will notice the same thing as long as the speed is consistent. You will not feel a thing when the speed is consistent, but when you slow down, accelerate, or make a turn, then you will feel forces against you.
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Jonas
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Re: Help me understand how it is that the Earth spins

Post by Jonas »

Hashi, I'm not saying you can't post these questions here - by all means go ahead if you just want to ask people who sort of know you.

However, you might be interested in this forum: http://reddit.com/r/askscience

Frankly I kind of think DDL might too - he'd fit right in :lol:
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that guy
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Re: Help me understand how it is that the Earth spins

Post by that guy »

oh sure. Have a physics question so ask the biochemist :P.

As for the ant on the rock:

It's important to keep in mind that the rock (earth) is an accelerating frame of reference. In order to remain the same distance from the center while spinning about the center you are actually accelerating towards the center. If you weren't then you would just shoot off into space in the linear direction you were traveling. To prove this to yourself, draw a circle and for a bunch of points on the circle draw a linear arrow showing the direction of movement about the circle. You'll notice the arrows don't all point in the same direction. If those arrows represent velocity and acceleration is the rate of change of velocity then since the velocity is clearly changing then there must be acceleration (To prove that it's towards the center of rotation would require a slightly cleverer example). In the case of the earth that acceleration is supplied by gravity. Given the right balance of gravitational force and travel speed it would be possible for acceleration due to gravity to exactly match the acceleration required to maintain the same circular (actually elliptical) path. That's how the moon orbits the earth. If the moon was moving faster it would just fly off. If gravity were stronger the moon would crash into the earth.

Returning to the rock and ant example consider the amount of acceleration holding an ant to a rock in space. Since the acceleration of the ant towards the rock is proportional to the mass of the rock and inversely proportional to the radius of the rock squared (assuming the ant is comparatively small) then this acceleration would be very small for a reasonable sized rock (a rock that was 2 meters across and weighed 1kg would only cause the ant to accelerate at about 0.6 trillionths of a meter per second per second). As such, unless the ant was stuck to the rock somehow, the rock would have to be spinning incredibly slowly for the ant to stay on its surface.

An interesting thing to note is that you may think therefore that there must be a force that is pushing the ant off the rock. This is not technically the case. Often it is treated as a sort of virtual force called centripetal force but it's actually just conservation of momentum at work. Newtons basic force equations only work for inertial (non-accelerating) frames of reference. This essentially comes down to things moving in a straight line in space. If I understand correctly, this same distinction is what forced Einstein to come up with his general theory of relativity because his special theory of relativity was a special case that only worked in inertial frames
Cybernetic pig
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Re: Help me understand how it is that the Earth spins

Post by Cybernetic pig »

Care to explain the 6 force-carrying particles in layman's terms (if that is even possible)?
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DaveW
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Re: Help me understand how it is that the Earth spins

Post by DaveW »

Cybernetic pig wrote:Care to explain the 6 force-carrying particles in layman's terms (if that is even possible)?
You could do worse than reading through the Standard Model page on Wikipedia. Probably goes into too much detail but you should be able to get the gist of it.

What you're looking for is Bosons, specifically gauge bosons.
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