The speed of an object on the equator of the earth

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robinson
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Re: The speed of an object on the equator of the earth

Post by robinson »

Let’s make it even easier

Instead of you spinning, just hold out you hand over you head, and stand on the equator

Now you can say your hand is moving at 1000 mph
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robinson
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Re: The speed of an object on the equator of the earth

Post by robinson »

Climb a tall mountain and now your hand is moving even faster!

Looking down at another person, several miles below, you can say your hand is moving faster than their hand


Hell, even at sea level your hand is moving faster than the speed of sound! It’s actually supersonic!
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Re: The speed of an object on the equator of the earth

Post by Anaxagoras »

It's not moving to the east, because east is only a direction relative to the surface of the earth, which is a curved surface, but it is moving in a circle around the axis of the earth.
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Re: The speed of an object on the equator of the earth

Post by ceptimus »

Put the camera on the moon, looking at Earth so that north is up. The camera sees the Earth's equator moving right at 1000 mph at the centre, coming towards the camera on the left hand limb and going away from the camera on the right.

If you're concerned about the velocity due to spin, try working out how fast the whole Earth has to go to get around the sun each year. From memory it's about 85,000 mph.

...and then the whole solar system is orbiting around the Milky Way even faster than that, and our whole galaxy is moving yet faster than that relative to other nearby galaxies...
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Re: The speed of an object on the equator of the earth

Post by Rob Lister »

You guys are wasting your time.
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Re: The speed of an object on the equator of the earth

Post by Hotarubi »

Rob Lister wrote: Wed Oct 14, 2020 7:15 pm You guys are wasting your time.
Correct. Thread needs graphs.
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robinson
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Re: The speed of an object on the equator of the earth

Post by robinson »

ceptimus wrote: Wed Oct 14, 2020 5:32 am Put the camera on the moon, looking at Earth so that north is up. The camera sees the Earth's equator moving
That was my first placement of the camera, which showed that an object on the equator, from the moons POV, isn’t moving East at 1000 mph

But because the moon is moving, it alters the total 24 hour distance as well

Also the moon is not usually over the equator, so that also changes things

But in any case, you don’t get a 1000 mph speed using the moon as the POV
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Re: The speed of an object on the equator of the earth

Post by ceptimus »

The moon takes about 28 days to orbit so reduces the apparent equator speed by less than 4%. This actually makes the speed closer to 1,000mph, because it's 1,037 mph from more 'stationary' positions such as the sun-earth Lagrange points.
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Re: The speed of an object on the equator of the earth

Post by Abdul Alhazred »

OK. Now how about the speed at 45 degrees latitude? :)
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Re: The speed of an object on the equator of the earth

Post by ceptimus »

Just multiply the equator speed by the cosine of the latitude: cos(45) = sqrt(2)/2, so the speed at that latitude = 1,037 * sqrt(2)/2 = 733 mph.
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Re: The speed of an object on the equator of the earth

Post by Abdul Alhazred »

ceptimus wrote: Thu Oct 15, 2020 1:00 pm Just multiply the equator speed by the cosine of the latitude: cos(45) = sqrt(2)/2, so the speed at that latitude = 1,037 * sqrt(2)/2 = 733 mph.
Hmm. About the speed of a commercial jet. 8)
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Re: The speed of an object on the equator of the earth

Post by robinson »

Anaxagoras wrote: Wed Oct 14, 2020 5:12 am It's not moving to the east, because east is only a direction relative to the surface of the earth, which is a curved surface, but it is moving in a circle around the axis of the earth.
I see you are on board with the first thing NASA has wrong


Now about that 1000 mph thing
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Re: The speed of an object on the equator of the earth

Post by robinson »

To save time, there is only one POV that allows a 1000 mph measurement, but it is a moving camera position that has incredibly complicated motion, not actually possible in the real world

It also only works for a very limited time frame
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Re: The speed of an object on the equator of the earth

Post by Pyrrho »

Image
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Re: The speed of an object on the equator of the earth

Post by robinson »

What speed is the camera?
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Re: The speed of an object on the equator of the earth

Post by robinson »

The real obstacle is, of course, we are used to measuring speed or velocity in reference to the unmoving ground.

If a supersonic aircraft was doing 1000 mph, staying directly over the equator, heading East, nobody would say it was doing 2000 mph heading East

Or if going west, not moving at all. But if we accept that an object on the equator is going 1000 mph heading East, that is exactly the facts of the matter. So our unmoving aircraft headed west at 1000 mph is not moving, in relation to the planet. But of course that isn’t true
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Re: The speed of an object on the equator of the earth

Post by robinson »

A satellite in a much higher altitude, at just the right speed, over the equator, would be like the camera in the animation above. But the last thing anybody would say, is that it is standing still in relation to the planet. It would be going very very fast, in regards to it’s movement in a very large orbit.

The software I linked to shows just how fast
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Re: The speed of an object on the equator of the earth

Post by Anaxagoras »

Do you think the earth spins or not? Usually we measure the speed at which it spins in relation to the sun, which gives the result of one full rotation every 24 hours. Divide the circumference of the earth at the equator in miles by 24 and that's the speed at the equator in mph. Relative to the sun, of course.

There's also something called a sidereal day if you want to measure the speed of rotation relative to more distant stars to account for the fact that the earth is orbiting the sun once every 365.25 days. A sidereal day is slightly less than 24 hours.
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Re: The speed of an object on the equator of the earth

Post by robinson »

Of course the earth is spinning
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Re: The speed of an object on the equator of the earth

Post by ceptimus »

I remember an interminable discussion on a forum or newsgroup concerning whether the moon rotates around its polar axis *, with respect to Earth.

One group maintained that because the moon always shows its same face to the earth, then it doesn't rotate. The other group argued that the moon rotates exactly once per lunar month - and that it has to do this so that it can always point its same hemisphere at Earth as it goes around its orbit.

The stupid thing was that everyone agreed exactly about the moon's motion - they just enjoyed arguing about the correct form of words to use to describe that motion.

This thread is now occupying the same territory of stupid.

* I assume that the group that said the moon doesn't rotate would argue about the very existence of a moon polar axis - but you know what I mean.