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

[singh94]

Interesting, are you proposing that your mothers eggs, fathers sperm, mothers womb etc aren't rotating with the earth?

I thought that would be the reply but i wasnt sure so any ways tell me atleast one thing must have come into existence... so atlest one thing would have required friction or some force.
so we come back to the same point... how did the first of the things to come into being start rotating with earth/ ans that and your theory according to me is foolproof.

 

[Doc Al]

if the frictional force is constant ... and the Earth's speed be constant, how can we attain equilibrium?

It's not constant. (Have you read this thread from the beginning?)

Another doubt... so we are moving with a speed of 1000miles per hourin west to est direction... if i start runnning in the east to west direction at 5 miles per hour then what should be my real speed... 995miles in the west to east direction or what?

What do you mean by 'real speed'? Speed is relative.

do i need to exert a force of 1005 miles per hour because if not then i am running in 2 opposite directions at the same time which is definitely not possible

A speed is not a force. And if you are moving at a constant velocity, the net force on you is zero. (Of course, on Earth you'll be centripetally accelerating.)

 

[JaredJames]

I thought that would be the reply but i wasnt sure so any ways tell me atleast one thing must have come into existence... so atlest one thing would have required friction or some force.
so we come back to the same point... how did the first of the things to come into being start rotating with earth/ ans that and your theory according to me is foolproof.

What first things to come into being?

Your father and mother are rotating with the earth, when you grow in your mother you are also rotating. The molecules you are made from have always been rotating with the earth.

It is only when you go back to the origins of Earth that this argument is relevant. At which point, frictional forces come into play and are what set them in motion.

You are arguing that a human life being created is some mystical process and the molecules, particles, atoms etc "pop" into existence at that point and need to be accelerated. This is non-sense. You are made from materials already existing on the planet, moving with the planet.

 

[singh94]

It's not constant. (Have you read this thread from the beginning?)

What do you mean by 'real speed'? Speed is relative.

A speed is not a force. And if you are moving at a constant velocity, the net force on you is zero. (Of course, on Earth you'll be centripetally accelerating.)

i know a speed is not a force but to acquire a speed that i didnt posses initially i neeeda force also const velocity doesn't need force but aquiring a velocity which didnt exist before needs one.
By real i mean to a person on Earth who can see me. Also while at it... a person who is in space out of Earth's atmosphere.

 

[cepheid]

if the frictional force is constant ... and the Earth's speed be constant, how can we attain equilibrium?
Another doubt... so we are moving with a speed of 1000miles per hourin west to est direction... if i start runnning in the east to west direction at 5 miles per hour then what should be my real speed... 995miles in the west to east direction or what?

There is no absolute notion of what is at rest and what is moving. All motion is relative. Speed is something that depends on the reference frame in which it is measured. In your example above, your velocity relative to the surface of the Earth is 5 mph, westward. Your velocity as measured in an inertial reference frame is 995 mph, eastward. Both statements are equally valid.

ido i need to exert a force of 1005 miles per hour because if not then i am running in 2 opposite directions at the same time which is definitely not possible

This statement is nonsense. Force is not measured in miles per hour. Miles per hour is a unit for velocity or speed. I would highly recommend first reading up on some basic physics, and then later moving on to concepts like relative motion, before posting further on this issue.

EDIT: Beaten by a longshot!

 

[JaredJames]

a person who is in space out of Earth's atmosphere.

So? Is there a point to this statement?

 

[singh94]

What first things to come into being?

Your father and mother are rotating with the earth, when you grow in your mother you are also rotating. The molecules you are made from have always been rotating with the earth.

It is only when you go back to the origins of Earth that this argument is relevant. At which point, frictional forces come into play and are what set them in motion.

You are arguing that a human life being created is some mystical process and the molecules, particles, atoms etc "pop" into existence at that point and need to be accelerated. This is non-sense. You are made from materials already existing on the planet, moving with the planet.

see u r coming back to friction which is all we have been arguing about... so instead of talking about the origin of Earth time why not explain the frictional force at this time as it will be more convinient.
I am talking about anything hat came into existense dropped on Earth from space from outer space anything which was not on Earth initially. not about u and me being born so now instead of cutting my statements please answer them.

 

[singh94]

There is no absolute notion of what is at rest and what is moving. All motion is relative. Speed is something that depends on the reference frame in which it is measured. In your example above, your velocity relative to the surface of the Earth is 5 mph, westward. Your velocity as measured in an inertial reference frame is 995 mph, eastward. Both statements are equally valid.



This statement is nonsense. Force is not measured in miles per hour. Miles per hour is a unit for velocity or speed. I would highly recommend first reading up on some basic physics, and then later moving on to concepts like relative motion, before posting further on this issue.

EDIT: Beaten by a longshot!

i thought u people would be and mature enough to understand that I am 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.

 

[JaredJames]

see u r coming back to friction which is all we have been arguing about... so instead of talking about the origin of Earth time why not explain the frictional force at this time as it will be more convinient.
I am talking about anything hat came into existense dropped on Earth from space from outer space anything which was not on Earth initially.

Read the thread, it's discussed it from the start.

not about u and me being born so now instead of cutting my statements please answer them.

Are you not, perhaps a quote of your earlier post:

Yes... but we come into existence when we are born so we have to be at rest first before we start moving with inertia.

Oh look, I'm not cutting anything up, I'm directly answering what you write.

 

[Doc Al]

I am talking about anything hat came into existense dropped on Earth from space from outer space anything which was not on Earth initially. not about u and me being born so now instead of cutting my statements please answer them.

Have you already forgotten your earlier post?

Yes... but we come into existence when we are born so we have to be at rest first before we start moving with inertia.

 

[singh94]

So? Is there a point to this statement?

i mean what is my speed relative to a person who is in free space away from all forces and at compele rest.

 

[JaredJames]

i thought u people would be and mature enough to understand that I am 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.

No, you don't.

If you are already at 1000mph, you only need to exert a force to give you an additional 5mph.

also i know what r the units of force velocity etc. which concern physics thank u very much.

Then show you do, stop posting statements which don't make sense and have incorrect units.

 

[Doc Al]

i mean what is my speed relative to a person who is in free space away from all forces and at compele rest.

Sorry, but the idea of something being at 'complete rest' is nonsensical. All motion is relative.

And being free from all forces would not define a velocity anyway. It just would mean that the velocity would remain constant (with respect to any inertial frame).

 

[singh94]

have you already forgotten your earlier post?

i am talking about anything that came on Earth when it was being created. Any thing from outer space (meteors aliens gases anything which was just moving in a straight line towards Earth due to its inertia or the Earth's gravitational field.
Now do u get wat i am trying to say?

 

[Doc Al]

i am talking about anything that came on Earth when it was being created. Any thing from outer space (meteors aliens gases anything which was just moving in a straight line towards Earth due to its inertia or the Earth's gravitational field.
Now do u get wat i am trying to say?

No, not at all.

 

[singh94]

Sorry, but the idea of something being at 'complete rest' is nonsensical. All motion is relative.

And being free from all forces would not define a velocity anyway. It just would mean that the velocity would remain constant (with respect to any inertial frame).

I am on Earth okay? i move in e-w at 5 miles per hour now wat is my speed for a person whos inertia of state is at rest and wh is not under an external forces?
also answer my other question concerning force for quiring speed of 1005 miles

 

[singh94]

No, not at all.[/QUOTE
then i give up trying to explain to u. maybe someone else will be able to.

 

[singh94]

I am on Earth okay? i move in e-w at 5 miles per hour now wat is my speed for a person whos inertia of state is at rest and wh is not under an external forces?
also answer my other question concerning force for quiring speed of 1005 miles

r u there Mr.Doc Al?

 

[Doc Al]

I am on Earth okay?

I'll accept that for the moment.

i move in e-w at 5 miles per hour now wat is my speed for a person whos inertia of state is at rest and wh is not under an external forces?

Again, a person who is 'at rest' is meaningless. Do you mean a person on Earth who is at rest with respect to earth? If so, then the relative speed is 5 mph, of course.

also answer my other question concerning force for quiring speed of 1005 miles

The force needed to change one's velocity depends on (1) how big a change you want and (2) how fast you want to change.

 

[D H]

Stop using text-speech, singh94. The correct wording is you rather than u, I rather than i, what rather than wat, are rather than r.

 

[singh94]

I'll accept that for the moment.

Again, a person who is 'at rest' is meaningless. Do you mean a person on Earth who is at rest with respect to earth? If so, then the relative speed is 5 mph, of course.

The force needed to change one's velocity depends on (1) how big a change you want and (2) how fast you want to change.

i mean a person who is in space. if everything was not moving(not at respect to each other but in actual) then he would be at rest with respect to them. now do u get it

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 don't 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

 

[singh94]

Stop using text-speech, singh94. The correct wording is you rather than u, I rather than i, what rather than wat, are rather than r.

Gee i didn kno dat :)

 

[JaredJames]

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 don't 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 traveling at 1005mph east or 995mph east. Put simply, you are always traveling east unless you are going faster than 1000mph in a westerly direction.

 

[Doc Al]

i mean a person who is in space. if everything was not moving(not at respect to each other 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 don't 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.

 

[singh94]

No, you don't have two velocities.

You are either traveling at 1005mph east or 995mph east. Put simply, you are always traveling east unless you are going faster than 1000mph in a westerly direction.

yes u r right.

 

[JaredJames]

Gee i didn kno dat :)

I didn't know that

yes u r right.

you are

Really? Asking for trouble after being warned.

 

[singh94]

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 Earth's center my v would be zero as the displacement is zero.

 

[singh94]

I didn't know that


you are

Really? Asking for trouble after being warned.

i don't kno wether it is u jarednjames or the original person but know that u can't force me to stop writing in short forms just cause u don't like it. either u bear with me, or u ignore me but stop trying to bully me OK?

 

[Doc Al]

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 Earth's 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.)

 

[JaredJames]

i don't kno wether it is u jarednjames or the original person but know that u can't force me to stop writing in short forms just cause u don't 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.

 

[Doc Al]

i don't kno wether it is u jarednjames or the original person but know that u can't force me to stop writing in short forms just cause u don't 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.

 

[singh94]

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.

 

[singh94]

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

 

[singh94]

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 Earth's surface to the center remains same.

 

[Doc Al]

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 Earth's 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.)

 

[jtbell]

u can't 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.

 

[JaredJames]

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 Earth's 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 traveled and speed is many times greater.

 

[cepheid]

i thought u people would be and mature enough to understand that I am 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.

 

[D H]

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.

 

[cepheid]

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?

 

[asdofindia]

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.

I thought conservation of angular momentum was applicable only to a rigid body rotating on its own axis. In that case we'd have to be glued to Earth's surface from time immemorial.

(But that's what the gravitational force and friction do. Gluing us to the surface)

So, the answer is a complex interplay of conservative and non-conservative forces, and conservation of motion.

 

[Drakkith]

I agree with asdofindia. It is a result of several forces over a long period of time. But in the short term, we don't need friction to keep us rotating with the earth.

 

[asdofindia]

Imagine a magnetic sphere. Rotating.
Imagine a sticky man on it with iron legs. Let's say he already has acquired the velocity of the point right under his legs.
At every point, the man's velocity wants him to go tangential to the surface, to be thrown away from the sphere.
But the magnetic force pulls him onto the sphere.
(Centrifugal and centripetal forces)
Agreed till now?
The centrifugal force and centripetal forces are exactly opposite and cancel each other. But they've got no component along the surface of the sphere!
(So there's got to be friction?!?!)
I don't think I've understood my answer.

 

[Drakkith]

The centrifugal force and centripetal forces are exactly opposite and cancel each other. But they've got no component along the surface of the sphere!

What do you mean by this?

 

[asdofindia]

See, if we draw a free body diagram. We'd draw an arrow from the man to the centre, calling it centripetal force. And another opposite to it calling it centrifugal force, right?
I thought they'd cancel, but I don't think I've clearly finished that thought process, I made a quick reply...

And of course they wouldn't have any component tangential to the surface.

But a body already moving with a velocity tangential do not need a force to keep it moving along the tangent.
But that's along the tangent...

Oh... I think I'm confused. Let me think for a while...

 

[Drakkith]

The force holding the man to your sphere is the magnetic force between his legs and the sphere. This force is greater than the upward force trying to push him away. If it wasn't any small simply movement by the man would send him moving upwards and away.

Because of this, the man is constantly being pulled down towards the sphere while also moving...tangently??...through space around the sphere. The magnetic force on him is similar to the gravitational force on a satellite in orbit. The satellite is constantly falling towards the earth, but also moving, resulting in an orbit.

 

[asdofindia]

That makes me wonder whether or not to subtract mv²/r from GMm/r² when calculating the weight of a body

Edit:http://en.wikipedia.org/wiki/Centrifugal_force_(fictitious)#Earth"
Appears like there are effects due to centrifugal force

 

[Drakkith]

There are most definitely effects due to the centrifigal force. They are usually so small as to be irrevelent in day to day stuff. However, for space launches we do calculate that effect as well as the velocity of the Earth's rotation from the launch site in order to put something into orbit correctly.

 

[asdofindia]

Centripetal force, F_g=GMm/r²
Centrifugal force, F_r=mv²/r
So, when v is > v_max where v_max> \sqrt{GM/r} we do fly away! If it's \sqrt{2} times the v_max in the above equation, it'd escape Earth's gravity too (because that'd be 11.2 km/s)
If v/v_max is between 1 and \sqrt{2}, it'd fly away and fall down back.
(But luckily on earth, v is approximately 1/17 times v_max)
That's why we're not flying away from earth.

Now, let me do something I've never done before.

Since the centrifugal force on Earth is canceled out by the gravity (289 times stronger), we can safely assume the body to be at rest with respect to the reference frame of earth. (I don't know if that's right, because as I said, I've never done this before) (There'd be no longer any effects that'd be observed due to rotational motion of Earth with respect to the space around it)
So, since Earth and the body are both at rest (in that inertial frame) there wouldn't be the need of any frictional force.

We have to view this in the inertial frame of earth.

(I have understood my point)

 

[Lsos]

i mean a person who is in space. if everything was not moving(not at respect to each other but in actual) then he would be at rest with respect to them. now do u get it

I'm not sure what you are asking, but when you are in orbit in space then we can confidently say that you are NOT rotating with the earth. You are moving much, much faster than the Earth is spinning.

Now what happens when you re-enter the atmosphere? The atmosphere WILL slow you the fuk back down to it's own speed, and it will use extreme force to do so. The force is so great in fact, that whatever is re-entering must use some kind of heat shield, otherwise it will burn up with a brightness of the sun.

So you see what happens whenever something is not rotating with the earth. The Earth WILL slow or speed it up to match its own rotation, and violently so if need be. If you don't believe me go jump out of a moving car, and you'll see first hand how it feels when something is NOT rotating with the earth.