CONCEPT OF RELATIVE MOTION- How Can We Say That Planets revolve around Sun?

[TruthSeeker]

Modern Concept of motion tells that motion is a combined effect of the state of object and the observer.

We Know that Galileo was punished for supporting the Heliocentric Theory instead of Geocentric Theory.

So the Motion being relative say that both theories are not equally wrong?

So still Heliocentric Theory Being followed? Isn't this theory fully correct only if the concept of absolute motion prevails?

The Earth moves around the sun relative to the sun. The Sun moves around the Earth relative to the Earth. But the solar system moves around the galaxy, relative to the galaxy center. And the galaxy center moves around the solar system, relative to the solar system. And any object in the universe is static, in the center of the universe, relative to the rest of the universe.

However, there are other factors at play. For example, electromagnetism will create electromagnetic fields around every object. The movement of one object relative to another which has a large electromagnetic field and gravity will determine the shape and properties of the electromagnetic field and how it affects the objects in question. That is, because the electromagnetic field of the sun is more powerful than that of the Earth, the field of the sun has a greater effect on Earth's than vice-versa. We see that with comets as well (notice the tail they form when they get close to planets and the sun).

Position is relative, but there are other factors at play as well, which are relative too, but also affect influences and outcomes.

 

[brucep]

The problem is that it is just a transformation equation. It doesn't analyze the interactions causing the acceleration.

Attached to wrong post.

 

[brucep]

I agree. In my textbook, to derive the equation of relative velocity(constant velocity),it used a method. I used the same method to prove that acceleration is relative. I don't think there is no problem with that derivation.

Yes. you are right. Mathematics can be used to derive whatever you want. Mathematics being language of physics. we can actually use any sort of assumptions and mathematics helps us to make predictions from our assumptions. Mathematics does only that. Help us to make predictions. Nothing more.

Acceleration is not relative. What's relative is the changing instantaneous speed over the course of the acceleration and or deceleration. This is a cool site where you can get some information about the relationship between the acceleration and the instantaneous speed. Under no circumstance does acceleration effect the tick rate of clocks. It's the instantaneous relative speed over the course of the acceleration or deceleration that is the source of the changing tick rate of clocks. Just 'tossed' that in since so much confusion exists concerning this subject.
The Relativistic Rocket
http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

Since a = g you can derive g and just substitute a

http://www.khanacademy.org/science/...on-of-time--acceleration-and-initial-velocity

To derive g take the derivative of

dr/dTau = -(2M/r)^1/2

= 1/2[(2M)^1/2/r^3/2] dr/dTau = -M/r^2 [substitute -(2M/r)^1/2 for dr/dTau ] For Newton it's dr/dt =-(2M/r)^1/2

 

[brucep]

That's because we are confined to a single reference frame and our adaption to this condition.
I am Absolutely sure that the Planets should move around the Sun and Not Sun moving around a planet Earth is just the impression of our's. Don't you think that's wrong?

You can absolutely understand that different objects have different velocities and accelerations in different frames. So why should the concept of absolute be introduced?

Acceleration isn't frame dependent. If it was frame dependent g and the gravitational field would be frame dependent. The local measurement of acceleration is an invariant measurement.

 

[Russ_Watters]

Attached to wrong post.

Huh?

 

[ash64449]

I didn't use the word qualitative and don't know why you think it applies.

I mean Isn't Heliocentric Theory more accepted than Geocentric Theory? That's why i used the qualitative.

 

[ash64449]

The problem is that it is just a transformation equation. It doesn't analyze the interactions causing the acceleration.

Yes. you are right.

But that equation clearly says that rate at which other object sees is different.

I agree with the fact that acceleration(of force) can be felt. But if that particular object keeps on accelerating,it will sure affect the way he sees other object moving? Don't you agree on that way?

In other words, is everything that we see on our reference frame an illusion?

 

[ash64449]

The modern concept is the same as Galileo's (motion is relative) plus Einstein's (length contracts and time dilates at high relative speeds).


The Geocentric view was that all of the objects in the sky orbited Earth. This is feasible for most objects but not all. In particular the planets pose a problem, because they move quickly enough out of their expected orbit to appear in the wrong position. To explain this a complex system of epicycles was invented to try to account for their erratic trajectory. It was never quite satisfactory, no matter how many improvements were made to it.

Enter Galileo. His principal discovery was that Jupiter was orbited by its own moons. If those moons did not orbit Earth, then perhaps Jupiter did not orbit Earth. If Jupiter did not orbit Earth, then perhaps the rest of the known planets did not orbit Earth. If they did not orbit Earth then perhaps they orbited the Sun. If that were true, then perhaps the Earth orbited the Sun also. This set the stage for the Heliocentric view.

Enter Copernicus, Kepler and Newton. Copernicus proposes that the planets orbit the Sun. Kepler shows that the area swept out along the orbit accumulates at a fixed rate. Newton confirms both men's ideas through the invention of calculus and the discovery of the universal law of gravitation.


No. The planets obviously do not orbit the Earth. The Geocentric view is therefore wrong. The Heliocentric view is Copernicus's correction to this. It eliminates epicycles and accounts for Galileo's discovery of the moons of Jupiter.


It's not a theory. It's just a correction to the older incorrect beliefs that prevailed in medieval Europe.


No, it's fully correct once Kepler demonstrated the absolute rate of change of the area swept by an arc of an orbit. This is more fully proven and explained by Newton's calculus and his discovery of gravity.

Totally agreed with you.

A doubt. Is whatever we see in our reference frame an illusion? I mean we "see" sun and all planets orbit us in a strange way. So we can all put these events as an illusion?

 

[ash64449]

Acceleration isn't frame dependent. If it was frame dependent g and the gravitational field would be frame dependent. The local measurement of acceleration is an invariant measurement.

Einstein said that we cannot choose a reference frame where gravity of the earth vanishes when he tried to explain equivalence principle!!

 

[ash64449]

Acceleration is not relative. What's relative is the changing instantaneous speed over the course of the acceleration and or deceleration.

I am a little bit confused by this sentence. isn't Change is instantaneous velocity divided by time interval over which that change in velocity takes place an acceleration?

If changing instantaneous speed is relative,Why not acceleration?

 

[ash64449]

The above sounds confused. When you drop an object here on earth it does not fall at a constant velocity. It accelerates toward the ground at 32ft/sec/sec. .

Sorry OnlyMe!!! you were confused by my sentence. I am extremely sorry for that. Let me clarify what i mean so that you can help me clear my doubt.

According to me ,If Acceleration was not relative, Equivalence principle cannot be constructed.

Take for example a room that is floating in the outer space. A man is inside that room. Another man too is floating outside the room.

Now think someone from outside pulled the room with constant acceleration.(Very important: In the frame outside the room or according to the man outside the room). The man inside the room feels that force ,considers that the force is obviously pulling him down. But then too he considers himself as being at rest,(his frame:accelerated frame).

Now think that man inside the room has ball in his hand. he doesn't drop the ball. But just let go the ball from his hand. Man inside the room sees that the ball moves down with constant acceleration. He considers that room acts force on him and the ball and that's why ball falls down with that acceleration.

But how does the ball fall down with respect to the man outside?.

Room is accelerating outside the frame of the man outside. So when the man inside the room lets go the ball, acceleration to the ball is not imparted,relative to the man outside. So now the ball moves with constant velocity with respect to reference frame outside the room

So the fact is that Equivalence principle saying that acceleration is indistinguishable from gravity actually works in different frames.

Not that Ball is moving with constant velocity with respect to outside the room but moving with an acceleration with respect to man inside the room.

Man inside the room is accelerating with respect to man outside but not accelerating with respect to him. He is at rest. But he feels a force.

See.. Acceleration is relative. It is due to this why equivalence principle exists.

But as brucep said it will mean that acceleration due to gravity 'g' would vary according to different reference frame.

But it is impossible to take that sort of reference frame.

This is what i meant in the earlier post

 

[Russ_Watters]

I mean Isn't Heliocentric Theory more accepted than Geocentric Theory? That's why i used the qualitative.

That's not what qualitative means. Qualitative is a subjective judgement of aesthetic quality as opposed to quantitative, which is an objective judgement of calculation accuracy.

Yes. you are right.

But that equation clearly says that rate at which other object sees is different.

That's correct, but the fact that the time rate of change of distance can be calculated from either frame doesn't mean that either can be said to be accelerating. Objectively, the rocket that fires its engines is the one accelerating away from the other. Otherwise, you need to inject seemingly random gravitational fields that switch on and off conveniently at the same time the rocket fires/stops its engines.

I agree with the fact that acceleration(of force) can be felt. But if that particular object keeps on accelerating,it will sure affect the way he sees other object moving? Don't you agree on that way?

I'm not sure if I agree - it isn't a complete sentence and doesn't seem to say anything useful. How will the acceleration "affect the way he sees [the] other object moving"?

In other words, is everything that we see on our reference frame an illusion?

No. There is no such thing as an illusion here. Differences in choice of reference frames are not illusions, they are just choices on how to view it.

It is no more correct to call this an illusion than it is to look at someone's front and back and call those different views illusions.

 

[ash64449]

That's not what qualitative means. Qualitative is a subjective judgement of aesthetic quality as opposed to quantitative, which is an objective judgement of calculation accuracy.

Thank you!

That's correct, but the fact that the time rate of change of distance can be calculated from either frame doesn't mean that either can be said to be accelerating. Objectively, the rocket that fires its engines is the one accelerating away from the other. Otherwise, you need to inject seemingly random gravitational fields that switch on and off conveniently at the same time the rocket fires/stops its engines.
I'm not sure if I agree - it isn't a complete sentence and doesn't seem to say anything useful. How will the acceleration "affect the way he sees [the] other object moving"?

If the rate of change of distance is different is different frame, one has to consider that the other object is moving at that rate. I think that's what relative velocity is all about.

Say that in my reference frame, an object's velocity is 4m/s and in your frame 7m/s. What is the obvious meaning of this sentence?

The meaning is that in my reference frame, the object changes it's position at that rate and in your reference frame,object changes it's position at that rate.

But we "cannot" absolutely say at which rate that object is 'actually' changing(or moving).

If you Agree withe above,surly you have to agree with that statement that acceleration is relative due to the following argument:

Acceleration in other sense also represents particular change in the position too. Clearly change of position is different in different frames, that's why velocity( that's what velocity is) is relative.

But Acceleration represents change in velocity and a particular change in position too. So Acceleration should be relative.

Russ, I have replied just now to OnlyMe. Can you give me your opinion about my reply to him?

 

[Russ_Watters]

I am a little bit confused by this sentence. isn't Change is instantaneous velocity divided by time interval over which that change in velocity takes place an acceleration?

If changing instantaneous speed is relative,Why not acceleration?

Again, the math isn't at issue here. At issue is the cause and effect that makes the acceleration happen. You're trying to "win" this with word and math games instead of dealing with that reality.

 

[OnlyMe]

Sorry OnlyMe!!! you were confused by my sentence. I am extremely sorry for that. Let me clarify what i mean so that you can help me clear my doubt.

According to me ,If Acceleration was not relative, Equivalence principle cannot be constructed.

Take for example a room that is floating in the outer space. A man is inside that room. Another man too is floating outside the room.

Now think someone from outside pulled the room with constant acceleration.(Very important: In the frame outside the room or according to the man outside the room). The man inside the room feels that force ,considers that the force is obviously pulling him down. But then too he considers himself as being at rest,(his frame:accelerated frame).

Now think that man inside the room has ball in his hand. he doesn't drop the ball. But just let go the ball from his hand. Man inside the room sees that the ball moves down with constant acceleration. He considers that room acts force on him and the ball and that's why ball falls down with that acceleration.

But how does the ball fall down with respect to the man outside?.

Room is accelerating outside the frame of the man outside. So when the man inside the room lets go the ball, acceleration to the ball is not imparted,relative to the man outside. So now the ball moves with constant velocity with respect to reference frame outside the room

So the fact is that Equivalence principle saying that acceleration is indistinguishable from gravity actually works in different frames.

Not that Ball is moving with constant velocity with respect to outside the room but moving with an acceleration with respect to man inside the room.

Man inside the room is accelerating with respect to man outside but not accelerating with respect to him. He is at rest. But he feels a force.

See.. Acceleration is relative. It is due to this why equivalence principle exists.

But as brucep said it will mean that acceleration due to gravity 'g' would vary according to different reference frame.

But it is impossible to take that sort of reference frame.

This is what i meant in the earlier post

I think I see the issue now.

To begin acceleration has a very clear definition. It is not a relative issue in the sense that it seems you are describing. It is not defined by how fast two objects move toward or away from eachother. It is defined as the changing rate of motion, of an individual object or observer. That can be increasing speed or decreasing speed and/or a change in direction described as a changing velocity.

When acceleration is not the result of free fall in a gravitational field, which could be an orbit or falling off a roof, acceleration can be measured as the object's or observer's resistance to the constantly changing speed or velocity.

Now with that in mind turn back to your box in space example, an example which works well in describing the equivalence principle. To the man in the box who sees nothing outside the box, the experience and measurements are no different than if he/she were standing on the ground on earth. This is what the equivalence principle is attempting to describe.., without information from outside the box, the man in the box cannot say that the box is not just sitting on the ground some where.

From outside the box, or even from inside if the man inside has information from outside the box, it is clear that the box is accelerating and the man standing inside the box is accelerating. When the man in the box lets go of a ball, it is true that he cannot tell that it does not accelerate toward the floor and that an observer outside the box could know that it no longer accelerates.

What each observer "sees" is not an illusion. But for either of them to draw conclusions about acceleration requires more information than is available from within the box. With all the necessisary information it becomes clear that the box and the man in the box are accelerating and once the man lets go of the box its motion is inertial.., moving at a constant velocity with the floor of the box accelerating toward it.

 

[OnlyMe]

Again, the math isn't at issue here. At issue is the cause and effect that makes the acceleration happen. You're trying to "win" this with word and math games instead of dealing with that reality.

Russ I don't think that ash is trying to win anything here. Keep in mind that he/she is working from grade 11 course work and seems to be exploring these concepts beyond what is going on in class.

I am a little bit confused by this sentence. isn't Change is instantaneous velocity divided by time interval over which that change in velocity takes place an acceleration?

If changing instantaneous speed is relative,Why not acceleration?

Ash, instantaneous speed is speed at one point — one instant. Even for an accelerating object at any one point it has an instantaneous speed. Time is not involved. The instantaneous speed between two objects or observers is relative, but it involves only an instant in time.

Acceleration is not relative. Acceleration occurs over time, and the object's inertial resistance to the changing velocity can be measured. (Again except where the acceleration is the result of free fall due to gravity.)

Don't confuse an accelerating change in the distance between objects, with acceleration.

I think Russ has been trying to point out that the math does not always describe all of the real life conditions, without some real life context.

 

[brucep]

I am a little bit confused by this sentence. isn't Change is instantaneous velocity divided by time interval over which that change in velocity takes place an acceleration?

If changing instantaneous speed is relative,Why not acceleration?

Because it's not a frame dependent quantity. All speed and velocity are relative. Look at the units for acceleration and velocity. For velocity it's meters per second [m/s] and for acceleration it's meters per second per second [m/s^2]. Acceleration and or deceleration require force. If acceleration was frame dependent then you could eliminate the gravitational field just by changing frames. Newton's 2nd law would be frame dependent. This is physics not semantics.

 

[brucep]

Sorry OnlyMe!!! you were confused by my sentence. I am extremely sorry for that. Let me clarify what i mean so that you can help me clear my doubt.

According to me ,If Acceleration was not relative, Equivalence principle cannot be constructed.

Take for example a room that is floating in the outer space. A man is inside that room. Another man too is floating outside the room.

Now think someone from outside pulled the room with constant acceleration.(Very important: In the frame outside the room or according to the man outside the room). The man inside the room feels that force ,considers that the force is obviously pulling him down. But then too he considers himself as being at rest,(his frame:accelerated frame).

Now think that man inside the room has ball in his hand. he doesn't drop the ball. But just let go the ball from his hand. Man inside the room sees that the ball moves down with constant acceleration. He considers that room acts force on him and the ball and that's why ball falls down with that acceleration.

But how does the ball fall down with respect to the man outside?.

Room is accelerating outside the frame of the man outside. So when the man inside the room lets go the ball, acceleration to the ball is not imparted,relative to the man outside. So now the ball moves with constant velocity with respect to reference frame outside the room

So the fact is that Equivalence principle saying that acceleration is indistinguishable from gravity actually works in different frames.

Not that Ball is moving with constant velocity with respect to outside the room but moving with an acceleration with respect to man inside the room.

Man inside the room is accelerating with respect to man outside but not accelerating with respect to him. He is at rest. But he feels a force.

See.. Acceleration is relative. It is due to this why equivalence principle exists.

But as brucep said it will mean that acceleration due to gravity 'g' would vary according to different reference frame.

But it is impossible to take that sort of reference frame.

This is what i meant in the earlier post

No the equivalence principal says that a = g. Inertial mass is equivalent to gravitational mass. mass is an invariant. It's not frame dependent. If you want to think acceleration is frame dependent [relative] go for it.

 

[Aqueous Id]

Totally agreed with you.

A doubt. Is whatever we see in our reference frame an illusion? I mean we "see" sun and all planets orbit us in a strange way. So we can all put these events as an illusion?

Good question. Plato wonders about "seeing the Sun in its proper place and not another" in his remarkable treatment of illusion.

 

[ash64449]

Again, the math isn't at issue here. At issue is the cause and effect that makes the acceleration happen. You're trying to "win" this with word and math games instead of dealing with that reality.

Sorry if you felt that way. I wasn't trying to 'win' at all.