# Why do we rotate along with the earth's rotation?

by Astaroth
Tags: earth, rotate, rotation
 Share this thread:
P: 3,387
 Quote by singh94 finally i am on earth and moving with the earth constant speed of 1000 miles. if i move in opposite direction at a speed of x miles per hour and i reach the speed in 1 second then why dont i need a force of which can give me a speed of 1000+x miles in opposite diretion in 1 sec. otherwise i have two different velocities at same time 1000 miles in earth direction an five miles in opposite direction which is not possible
No, you don't have two velocities.

You are either travelling at 1005mph east or 995mph east. Put simply, you are always travelling east unless you are going faster than 1000mph in a westerly direction.
Mentor
P: 41,564
 Quote by singh94 i mean a person who is in space. if everything was not moving(not at respect to eachother but in actual) then he would be at rest with respect to them. now do u get it
Just being 'in space' does not determine an object's velocity. It can have any allowable speed.
 finally i am on earth and moving with the earth constant speed of 1000 miles.
OK.
 if i move in opposite direction at a speed of x miles per hour and i reach the speed in 1 second then why dont i need a force of which can give me a speed of 1000+x miles in opposite diretion in 1 sec. otherwise i have two different velocities at same time 1000 miles in earth direction an five miles in opposite direction which is not possible
Once again, a force is not associated with a velocity, but with a change in velocity. And that's only x mph.

As far as your velocity is concerned, that depends on what you are measuring it with respect to. With respect to the earth's surface, it would be x mph. With respect to the earth's center, it would be 1000 + x mph. With respect to the Sun, something else entirely. And so on.
P: 21
 Quote by jarednjames No, you don't have two velocities. You are either travelling at 1005mph east or 995mph east. Put simply, you are always travelling east unless you are going faster than 1000mph in a westerly direction.
yes u r right.
P: 3,387
 Quote by singh94 Gee i didn kno dat :)
I didn't know that
 Quote by singh94 yes u r right.
you are

Really? Asking for trouble after being warned.
P: 21
 Quote by Doc Al Just being 'in space' does not determine an object's velocity. It can have any allowable speed. OK. Once again, a force is not associated with a velocity, but with a change in velocity. And that's only x mph. As far as your velocity is concerned, that depends on what you are measuring it with respect to. With respect to the earth's surface, it would be x mph. With respect to the earth's center, it would be 1000 + x mph. With respect to the Sun, something else entirely. And so on.
change in velocity is being 1000miles in east to 5 miles in west. also with earths center my v would be zero as the displacement is zero.
P: 21
 Quote by jarednjames I didn't know that you are Really? Asking for trouble after being warned.
i dont kno wether it is u jarednjames or the original person but know that u cant force me to stop writing in short forms just cause u dont like it. either u bear with me, or u ignore me but stop trying to bully me OK?
Mentor
P: 41,564
 Quote by singh94 change in velocity is being 1000miles in east to 5 miles in west.
Huh? Are you moving 5 mph with respect to the surface or 1005 mph? Kind of makes a difference.

 also with earths center my v would be zero as the displacement is zero.
Huh? The surface of the earth is moving with respect to the center at 1000 mph. (Roughly speaking, at the equator.)
P: 3,387
 Quote by singh94 i dont kno wether it is u jarednjames or the original person but know that u cant force me to stop writing in short forms just cause u dont like it. either u bear with me, or u ignore me but stop trying to bully me OK?
Forum rules say you can't, you agreed to them on signing up.
Mentor
P: 41,564
 Quote by singh94 i dont kno wether it is u jarednjames or the original person but know that u cant force me to stop writing in short forms just cause u dont like it. either u bear with me, or u ignore me but stop trying to bully me OK?
Think twice about continuing to violate our rules.
P: 21
 Quote by jarednjames Forum rules say you can't, you agreed to them on signing up.
allright then if that is the case ill stop imediately but i may make some slips here or there.
P: 21
 Quote by Doc Al Think twice about continuing to violate our rules.
i APOLOGISE TO DOC AL JADERNJAMES AND ALL WHO TOLD ME TO STOP WRITING IN SHORT FORMS.
SORRY
P: 21
 Quote by Doc Al Think twice about continuing to violate our rules.
the earth is rotating the center may not move from its position but it is also rotating if u take the earth and shrink it to the size of the center of the earth then it would still rotate right? so the position of a point on earths surface to the center remains same.
Mentor
P: 41,564
 Quote by singh94 the earth is rotating the center may not move from its position but it is also rotating if u take the earth and shrink it to the size of the center of the earth then it would still rotate right? so the position of a point on earths surface to the center remains same.
No. Imagine a wheel spinning on its axle. The axle is fixed--its speed is zero (with respect to some frame). But the rim of the wheel is moving with respect to that frame. Same with the earth.

(Don't confuse rotational speed with translational speed.)
Mentor
P: 11,864
 Quote by singh94 u cant force me to stop writing in short forms
Hint: "Mentor" = "Moderator" here. Mentors have the power to ban people.

If you insist on using text-speak, you are welcome to find another physics forum that allows you to do so.
P: 3,387
 Quote by singh94 the earth is rotating the center may not move from its position but it is also rotating if u take the earth and shrink it to the size of the center of the earth then it would still rotate right? so the position of a point on earths surface to the center remains same.
The further out you move away from the centre of the earth, the greater the distance you travel and the higher your velocity becomes.

A good example is a geostationary satellite. It is constantly above one point on the surface of the earth, but it's distance travelled and speed is many times greater.
Emeritus
Sci Advisor
PF Gold
P: 5,196
 Quote by singh94 i thought u people would be and mature enough to understand that im just saying that do i need to exert a force which gives me a speed of 1005 miles so that i can run against the direction of the earth.also i know what r the units of force velocity etc. which concern physics thank u very much.
I know that this has already been answered, but I felt that I should respond since it was addressed to me:

1. You mean that you thought that we would be psychic enough that we would somehow be able to make (correct) assumptions about your level of physics knowledge, in spite of the fact that you failed to communicate that level clearly? Well, NO, we can't read your mind. All we have to go on when it comes to gauging your physics knowledge are the things that you write. EDIT: and besides, there is no such thing as "a force that gives you a speed of 1005 mph." Any force CAN give you that speed provided you apply it for long enough time. Once again, based on what you have typed, we have no choice but to assume that you don't understand the impulse-momentum theorem.

2. You DON'T have to "run against the direction of the Earth." It's NOT like being on a treadmill, because you are MOVING WITH THE EARTH. In other words, if you don't move, it means you are stationary with respect to the Earth's surface. Even when you are standing still, it appears to an outside observer (who is not rotating with the Earth) that both the Earth and you (on it) are rotating at the same rate. Do you get it now?

Also, read the rest of the thread. You do NOT need to invoke friction at any point in history (not even going back to Earth's formation) to understand why everything that makes up part of the Earth is rotating. Only conservation of angular momentum need be applied.
Mentor
P: 15,201
 Quote by cepheid You do NOT need to invoke friction at any point in history (not even going back to Earth's formation) to understand why everything that makes up part of the Earth is rotating. Only conservation of angular momentum need be applied.
That's going a bit too far. In the long term, you cannot apply conservation of angular momentum for the simple reason that the Earth's angular momentum has not been constant. the Earth's rotation rate was considerably higher (4-6 times higher!) shortly after the Moon formed compared to its current rate. The atmosphere and oceans are not moving around the Earth at 4-6 times Earth rotation rate precisely because of friction.
Emeritus
Sci Advisor
PF Gold
P: 5,196
 Quote by D H That's going a bit too far. In the long term, you cannot apply conservation of angular momentum for the simple reason that the Earth's angular momentum has not been constant. the Earth's rotation rate was considerably higher (4-6 times higher!) shortly after the Moon formed compared to its current rate. The atmosphere and oceans are not moving around the Earth at 4-6 times Earth rotation rate precisely because of friction.
Thanks. Yeah, that is a fair point. I failed to consider tidal effects.

Edit: but weren't the atmosphere and oceans being torqued on as well?

 Related Discussions Introductory Physics Homework 2 Precalculus Mathematics Homework 5 Earth 21 Classical Physics 1 Classical Physics 5