Galaxies

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Thanks for all the replies.....

One other question...for the mathematicians...

If I am standing still on the earth, and the earth spins on its axis, the earth rotates around the sun, the solar system moves within the galaxy, the galaxy is spinning and the galaxy is moving in X direction..... how fast am I moving...



If I am standing still; how fast am I moving.... I'm sure that one might even stump Gollum.

Relative to what?

 

[Wiccan_Child]

Thanks for all the replies.....

One other question...for the mathematicians...

If I am standing still on the earth, and the earth spins on its axis, the earth rotates around the sun, the solar system moves within the galaxy, the galaxy is spinning and the galaxy is moving in X direction..... how fast am I moving...



If I am standing still; how fast am I moving.... I'm sure that one might even stump Gollum.

Motion is relative, mon frère. How 'fast' you're going depends on how fast the observer is going: if I'm sitting on the Earth with you, it looks like you aren't moving at all. If I'm sitting on the Sun (and burning my bum), it looks like you're orbitting me at ~30000 m/s.

And then relativistic effects come in if it looks like you're going really fast .

 

[Allister]

Relative to what?

Myself? I don't know.

if I'm sitting on the Earth with you, it looks like you aren't moving at all. If I'm sitting on the Sun (and burning my bum), it looks like you're orbitting me at ~30000 m/s.

OK, so we're sitting on the earth. Can't we just add up the speeds?

Earth spin
+
Earth yearly orbit
+
Solar System speed
+
Galaxy rotation
+
Galaxy speed


So If I am sitting still how fast am I moving?

 

[Wiccan_Child]

Myself? I don't know.

From the point of view of yourself, you aren't moving at all.

From the point of view of someone on a train, you're whizzing past at several miles per hour.

OK, so we're sitting on the earth. Can't we just add up the speeds?

No!

Speed is a measure of how fast displacement changes. That is, how fast the distance between two points (say, one on Earth, one on the Sun) is changing.

We have your point (you're sitting still on the Earth). From which point are we measuring speed?

Earth spin
+
Earth yearly orbit
+
Solar System speed
+
Galaxy rotation
+
Galaxy speed


So If I am sitting still how fast am I moving?

Again, from whose point of view? Notice that a speed-camera records a car travelling at 70mph doesn't take into account its motion around the Sun. Why? Because the camera is also moving around the Sun. Relative to the camera, the car is moving at 70mph. Their movement round the Sun doesn't matter, because they're both moving round the Sun in exactly the same way.

When you're in a car, do you feel the wind rushing past your ears? No. Why? Because the air is moving with you. Relative to you, the air has zero speed. Relative to a tree outside, it's moving with the same speed as you (say, 30mph).

It's all relative.

 

[Avatar]

Allister, (seriously, no offense intended) but are you sure you're an atheist?

 

[Allister]

WC, I get what you're saying.

I am sitting on the earth. Not moving. zilch momentum. stationary.

BUT, the Earth is spinning, nay? So I am spinning too. How fast am I, as a part of the Earth moving?

The Earth orbits the Sun. I, sitting quietly in front of a fire, am also a part of the Earth. How fast am I moving.

The Solar system is moving. I, sitting quietly in front of a fire on a cold winter's night, as part of the earth, which is part of the solar system. How fast am I moving...

And so on.


It's a relative. Don't get all Einsteinian with me.

 

[Allister]

Allister, (seriously, no offense intended) but are you sure you're an atheist?

Completley. Don't mistake curiosity with stupidity.

I am not a scientist. I like to dabble in laymen science stuff but mostly it's not my thing.

Can't I ask questions from a layman's perspective without my non belief in sky people being questioned?

 

[Avatar]

Completley. Don't mistake curiosity with stupidity.

I am not a scientist. I like to dabble in laymen science stuff but mostly it's not my thing.

Can't I ask questions from a layman's perspective without my non belief in sky people being questioned?

Yes, of course. Again, I meant no offense.

 

[Wiccan_Child]

WC, I get what you're saying.

I am sitting on the earth. Not moving. zilch momentum. stationary.

With respect to something else on the Earth, yes. With respect to the Sun, no.

BUT, the Earth is spinning, nay? So I am spinning too. How fast am I, as a part of the Earth moving?

You're rotating around the centre of the Earth at a speed of ~463m/s. But that's only as viewed from the centre of the Earth.

The Earth orbits the Sun. I, sitting quietly in front of a fire, am also a part of the Earth. How fast am I moving.

You're orbiting the Sun at a speed of ~30000m/s. But again, that's only as viewed from the Sun.

From the point of view of the Earth (and you and I), it's the Sun that's orbiting us at ~30000m/s.

The Solar system is moving. I, sitting quietly in front of a fire on a cold winter's night, as part of the earth, which is part of the solar system. How fast am I moving...

And so on.

And so forth .

It's a relative. Don't get all Einsteinian with me.

It's Newtonian, actually. You can't ask "How fast am I moving?" without first specifying the motion of the person doing the measurement. There's no such thing as absolute motion (except for light, but that's special...)

 

[Allister]

Yes, of course. Again, I meant no offense.

No worries, no offense taken.

It's Newtonian, actually.

Oh, I saw the word relative and assumed Einstien was involved somewhere...

You can't ask "How fast am I moving?" without first specifying the motion of the person doing the measurement. There's no such thing as absolute motion (except for light, but that's special...)

I don't mean to go round and round in circles but.......huh?

Why can't we just add the speeds up?

OK, let's take the person sitting on the Earth out of the equation.

How fast is the Earth moving? It is spinning and it is orbiting the sun. It is also, simultaneously whizzing along with the solar system through the galaxy, which in turn is spinning.

Again, I don't mean to go round and round in circles but I don't see why it isn't possible to calculate the overall speed of the Earth, given all the crazy movement that's going on.

 

[ragarth]

Why can't we just add the speeds up?

OK, let's take the person sitting on the Earth out of the equation.

How fast is the Earth moving? It is spinning and it is orbiting the sun. It is also, simultaneously whizzing along with the solar system through the galaxy, which in turn is spinning.

Again, I don't mean to go round and round in circles but I don't see why it isn't possible to calculate the overall speed of the Earth, given all the crazy movement that's going on.

Let's simplify the system. You're in deep space, there's nothing else around you except two asteroids: A and B. You stand upon asteroid A, and the two asteroids are approaching each other at a speed of 100 miles per hour.

Are you traveling 100mph, is the other asteroid travelling 100mph, is each asteroid traveling 50mph, or some other fraction of 100 apiece?

It's relative. Depending on your point of reference the speeds at which either asteroid is moving changes, whether that point of reference is asteroid A, B, or some position in space.

In your question, it sounds like you're attempting to make the center of the galaxy your reference point. This is good, but now we're getting into some crazy math because the vector of your motion changes due to the various circling orbits. In reference to the center of the galaxy, your speed changes based on the time of day and year due to the rotation of the earth around it's axis and the earth around the sun.

 

[ragarth]

1038mph person at equator
67000mph earth's orbit around the sun
447000mph sun around the galaxy

maximum speed of an individual on the planet with galactic center as reference:

1038+67000+447000= ~515038mph

minimum speed of an individual on the planet with galactic center as reference:

447000-67000-1038= ~378962mph

So, your speed around the galactic center will vary from ~515038mph to ~378962mph

 

[Allister]

Let's simplify the system. You're in deep space, there's nothing else around you except two asteroids: A and B. You stand upon asteroid A, and the two asteroids are approaching each other at a speed of 100 miles per hour.

Are you traveling 100mph, is the other asteroid travelling 100mph, is each asteroid traveling 50mph, or some other fraction of 100 apiece?

I'm with you... makes sense.

It's relative. Depending on your point of reference the speeds at which either asteroid is moving changes, whether that point of reference is asteroid A, B, or some position in space.

OK, but regardless of the observer both asteroids are moving at set speeds, yes? I mean, they're in space, once something starts moving it never stops or alters course, speeds up or slows down (barring outside influence). Their speeds don't vary.

So how fast are they moving?
How fast is the Earth moving?

In your question, it sounds like you're attempting to make the center of the galaxy your reference point.

What ever works best

This is good, but now we're getting into some crazy math because the vector of your motion changes due to the various circling orbits. In reference to the center of the galaxy, your speed changes based on the time of day and year due to the rotation of the earth around it's axis and the earth around the sun.

Can we not just reduce it to averages.

 

[Wiccan_Child]

Oh, I saw the word relative and assumed Einstien was involved somewhere...

Well, Einstein refined the idea with his theories of special and general relativity, but it was Newton who first figured out that there's no such thing as absolute motion. You can't say "this thing is travelling at this particular speed", because its speed looks different depending on how you're travelling.

I don't mean to go round and round in circles but.......huh?

Why can't we just add the speeds up?

Because think about what you want to add up. We have the Earth, the Sun, and the galactic core.

Sitting on the Earth, we're not moving at all. It's the Sun and core that are moving, and they have particular speeds. Not us.

Sitting on the Sun, it's the Earth and core which move, not us.

At the core, it's the Earth and Sun which move.


Consider two planets, A and B:

From the point of view of A, it is stationary and B is orbiting it.
But B sees it as stationary, and A orbiting it.
Which is right?

OK, let's take the person sitting on the Earth out of the equation.

How fast is the Earth moving? It is spinning and it is orbiting the sun.

Ah, no it's not. it's the Sun that orbits us. Just look up at the sky! You can see it moving, clear as day (unless it's night).

It is only when we take the Sun to be stationary that the Earth moves round in a nice ellipse. If we took the Earth as stationary, the Sun would move round us in a nice ellipse.

But which do we take, and why?

It is also, simultaneously whizzing along with the solar system through the galaxy, which in turn is spinning.

Again, I don't mean to go round and round in circles but I don't see why it isn't possible to calculate the overall speed of the Earth, given all the crazy movement that's going on.

Think about how it looks in your mind's eye. When you think about the solar system, you automatically centre on the Sun. Why? Because that's your reference point: you take that to be stationary, and everything else moves around it.

But if you took the Earth as stationary, everything would do exactly the same.

If you were given a diagram, there would be no way to tell the two apart.

 

[Allister]

1038mph person at equator
67000mph earth's orbit around the sun
447000mph sun around the galaxy

maximum speed of an individual on the planet with galactic center as reference:

1038+67000+447000= ~515038mph

minimum speed of an individual on the planet with galactic center as reference:

447000-67000-1038= ~378962mph

So, your speed around the galactic center will vary from ~515038mph to ~378962mph

515038mph.....

 

[Wiccan_Child]

OK, but regardless of the observer both asteroids are moving at set speeds, yes?

No .

 

[Allister]

From the point of view of A, it is stationary and B is orbiting it.
But B sees it as stationary, and A orbiting it.
Which is right?

Neither is orbiting the other. They are both moving.

It is only when we take the Sun to be stationary that the Earth moves round in a nice ellipse. If we took the Earth as stationary, the Sun would move round us in a nice ellipse.

But which do we take, and why?

Huh? Regardless of how we 'see' it, it is the Earth that orbits the Sun.

you take that to be stationary, and everything else moves around it.

Other than planetary moons everything does orbit the Sun.

But if you took the Earth as stationary, everything would do exactly the same.

But the Earth isn't stationary.

 

[Allister]

No .

And someone said Quantum Mechanics didn't make sense

 

[ragarth]

OK, but regardless of the observer both asteroids are moving at set speeds, yes? I mean, they're in space, once something starts moving it never stops or alters course, speeds up or slows down (barring outside influence). Their speeds don't vary.

So how fast are they moving?
How fast is the Earth moving?

We can say that the distance between the two asteroids is reducing at 100mph per second. But to assign a speed to each individual asteroid we need a point of reference. Between the two asteroids they're traveling 50mph, on asteroid A asteroid B looks like it's traveling 100mph, and on asteroid B asteroid A looks like it's traveling 100mph. motion is entirely relative to whatever you're measuring it at. How about another example?

Car A has 70mph showing on it's speedometer. Car B has 70mph showing on it's speedometer. They're on a collision course. That 70mph uses the earth as it's reference point (It's measured via the number of times the tires rotate per second, which are what propels the car across the planet's surface.) So in reference to the planet they're each traveling 70mph.

Now, car A has another car traveling beside it called Car C, and it's traveling at 60mph. Taking Car A and C only into account, the difference in their speeds is 10mph, so relative to Car C, car A is traveling at 10mph, and relative to Car A, Car C is traveling at -10mph (This is fluffed, speed is a scalar, so has no actual direction, by putting that negative sign in, it becomes a vector and so is technically now a velocity.) So, depending on your point of reference, Car A is traveling at 70mph or 10mph, and Car C is traveling at 60mph or -10mph.

Now let's take Car A and B and say they're headed directly at each other. Relative to the planet they're each traveling at 70mph, relative to each other they're each traveling at 140mph. This is empirically provable: If the two cars collide with a speed of 70mph apiece relative to the earth, the released momentum will be the same as two cars colliding if one is at 0mph and the other at 140mph relative to the earth. Conversely if we have a car traveling at 60mph, and a car traveling at 70mph rear ends it, the force of the collision is equivalent to that of a car traveling at 10mph colliding with a car traveling at 0mph.

Now, if that's too complex, let's use another example. Do you know those radar guns cops sometimes park at the side of the road to tell you your speed? Imagine one of them being towed by a truck at 10mph (relative to the earth). You're traveling towards it and your speedometer says 70mph(relative to the earth). The radar thing will, however, say 60mph because relative to it you are traveling 60mph.

 

[gaara4158]

No worries, no offense taken.



Oh, I saw the word relative and assumed Einstien was involved somewhere...





I don't mean to go round and round in circles but.......huh?

Why can't we just add the speeds up?

OK, let's take the person sitting on the Earth out of the equation.

How fast is the Earth moving? It is spinning and it is orbiting the sun. It is also, simultaneously whizzing along with the solar system through the galaxy, which in turn is spinning.

Again, I don't mean to go round and round in circles but I don't see why it isn't possible to calculate the overall speed of the Earth, given all the crazy movement that's going on.

I think I know where you're coming from. You assume that the universe is rigidly-shaped, and you just want to know how much space you are covering in a given amount of time. The problem is, we're not really sure that the shape of the universe is rigid; in fact, we observe that it is expanding. So as we ride this planet, there's no objective measure as to how much space we're covering in a given amount of time. Everything, even space, is moving relative to everything else.