Question of the Week - Old Version

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another_someone

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Re: Question of the Week - Old Version
« Reply #350 on: 17/06/2006 02:48:40 »
quote:
Originally posted by chris
"Why does a mirror reverse things in the horizontal, but not the vertical axis?"

Answers below please...



This is a question that comes up so often that I feel I should have a standard template with which to answer it.

A mirror does not reverse things.  What a mirror shows is a true image.  It is what we compare a mirror image to that is reversed.

You expect a mirror image to look like a person facing you.  The reason why a mirror image does not look like a person facing you is because the person facing you has turned around to face to.  It is the person who is facing you who is reversed.  The person who is facing you is reversed in the horizontal plane because (s)he has revolved around a vertical axis when turning around to face you.  If that person, rather than turning on their heals to face you, turned around by doing a handstand, then they would be reversed in the vertical plane and not in the horizontal plane.



George
« Last Edit: 17/06/2006 02:49:42 by another_someone »

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Offline chris

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Re: Question of the Week - Old Version
« Reply #351 on: 20/06/2006 09:49:44 »
But in terms of the physics of the light waves hitting the mirror, what's happening?

Chris

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ROBERT

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Re: Question of the Week - Old Version
« Reply #352 on: 29/06/2006 16:48:57 »
quote:
Originally posted by chris

But in terms of the physics of the light waves hitting the mirror, what's happening?



I found these sites on this subject:-
http://www.mathpages.com/home/kmath142.htm
http://www.mathpages.com/home/kmath354.htm
http://www.mathpages.com/home/kmath441.htm
« Last Edit: 30/06/2006 14:06:30 by ROBERT »

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ROBERT

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Re: Question of the Week - Old Version
« Reply #353 on: 29/06/2006 16:48:57 »
quote:
Originally posted by chris

But in terms of the physics of the light waves hitting the mirror, what's happening?



I found these sites on this subject:-
http://www.mathpages.com/home/kmath142.htm
http://www.mathpages.com/home/kmath354.htm
http://www.mathpages.com/home/kmath441.htm
« Last Edit: 30/06/2006 14:06:30 by ROBERT »

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Offline rochelle

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Re: Question of the Week - Old Version
« Reply #354 on: 10/07/2006 15:49:04 »
I have a question for you scientists! Lets see if you can answer this one. Tell me why.......tell me why I've never gotten goose bumps? I do get cold, and I do get the shivers, but goose bumps have never followed after experiencing those feelings.
 Hopefully someone will have an answer!
My bf's answer is that I have no soul, but thats obviously not a logical answer.

Rochelle Eloranta
 

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #355 on: 15/07/2006 05:57:23 »
Goose bumps are a vestige from the days when humans were covered with hair.

When it's hot and you need to cool down, little muscles at the base of each hair relax. Your hair becomes relaxed. Your sweat glands pump out body heat in sweat. Your blood vessels get big to take more heat to the skin to get rid of it. When it's cold, the arrector muscle pulls the hair up. The duct to the sweat glands gets small to conserve heat. Our blood vessels also get small to save heat.

Hair standing up doesn't make very good insulation - we don't have enough fur for that. Humans don't have very much hair on their bodies anymore. Millions of years ago, humans probably did. And that hair standing on end helped keep people warmer. Those little muscles we have on the end of each hair still work. They still make goose bumps.

Cold is not the only thing that can cause our hair to stand on end. Fear or anger can cause the same reflex. The same is true for other mammals. You'll notice that on a cat or dog. Their fur gets bigger when they're angry or afraid.


Perhaps you have some kind of genetic abnormailty that stops you from getting goosebumps. I have heard of someone who couldn't produce tears before but never the goosebumpless disease.

Sorry
Steven
« Last Edit: 03/08/2006 05:37:41 by Mjhavok »
Steven
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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #356 on: 03/08/2006 05:40:52 »
"Why does a mirror reverse things in the horizontal, but not the vertical axis?"

I think the entry in wikipedia below explains this quite well.

http://en.wikipedia.org/wiki/Reflection_(physics)

Steven
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Offline narasimeena

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Re: Question of the Week - Old Version
« Reply #357 on: 11/09/2006 20:20:34 »
quote:
Originally posted by NakedScientist

THIS WEEK'S QUESTION : - Have a go - brownie points to the person who gets closest to the correct answer, which we'll post in a week's time.

"WHY IS THE SKY BLUE ?"


This is mainly due an effect called as Tindall Effect a property of collides. "If you shine a beam of light through a solution, the light is not effected and passes through. If you shine the beam through a colloid the small aggregates scatter the light and the material looks cloudy or milky" This causes the sky to apprea blue.
Do I get a brownie for this!


Narasi Ramachandran
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Offline narasimeena

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Re: Question of the Week - Old Version
« Reply #358 on: 11/09/2006 20:22:52 »
"WHY IS THE SKY BLUE ?"

This is mainly due an effect called as Tindall Effect a property of collides. "If you shine a beam of light through a solution, the light is not effected and passes through. If you shine the beam through a colloid the small aggregates scatter the light and the material looks cloudy or milky" This causes the sky to apprea blue.
Do I get a brownie for this!



Narasi Ramachandran
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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #359 on: 12/09/2006 00:39:55 »
Yes, this question was answered a while back. :-D
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Offline David_D

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Re: Question of the Week - Old Version
« Reply #360 on: 13/09/2006 04:03:33 »
quote:
Our ancesters had much more hair than we do. In those days, when they became cold they would get goosebumps as a skin response which would raise the hairs on their body. ...


I've heard that humans have as many hairs as a chip, but our hair is much finer.
 

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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #361 on: 13/09/2006 20:23:44 »
Why it's dark in the night?
(It was a serious question).
« Last Edit: 15/09/2006 13:41:58 by lightarrow »

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #362 on: 11/10/2006 01:08:54 »
Hairy chips yuk. I prefer mine with salt and vinegar. lol.
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Offline science_guy

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Re: Question of the Week - Old Version
« Reply #363 on: 29/10/2006 08:07:32 »
Why it's dark in the night?
(It was a serious question).

I was taught that not as many photons reach the planet when the sun is on the other side.  The Earth's "night" side is not completely dark, because the light from the sun bounces off the moon and light shines from faraway stars.  More recently, though, light pollution from the lights in citys have made it harder to see stars.  The night sky is never completely dark.

That answer your question?
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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #364 on: 29/10/2006 09:55:08 »
No.
The question is very simple: why in the night there is not as such ligh as in the daylight? (Or almost, or more?).
I'm not talking about complete dark, just the usual concept of dark we all have.
(The answer is not trivial)
.
« Last Edit: 29/10/2006 09:58:06 by lightarrow »

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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #365 on: 21/11/2006 09:34:21 »
No one have any idea?

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Offline Heliotrope

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Re: Question of the Week - Old Version
« Reply #366 on: 28/11/2006 19:26:45 »
First of all define night. Then define dark.
Your answer will follow logically.

If not, I'll have a go at it when you have some definitions.
Reaching out to embrace the random, reaching out to embrace whatever may come.

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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #367 on: 29/11/2006 22:53:03 »
First of all define night. Then define dark.
Your answer will follow logically.
If not, I'll have a go at it when you have some definitions.


Night = the sun is behind the earth.
Dark = There is not enough light to play tennis or to read a book or to make precision work...

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Offline ukmicky

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Re: Question of the Week - Old Version
« Reply #368 on: 29/11/2006 23:31:31 »
Its dark at night for us humans because we have evolved to do most of our survival work (hunting and gathering) during daylight conditions. And therefore we have not been equipt with enough light collecting cells in our eyes or specialist systems like cats have for us us to see well in low light conditions.

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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #369 on: 30/11/2006 12:35:34 »
Its dark at night for us humans because we have evolved to do most of our survival work (hunting and gathering) during daylight conditions. And therefore we have not been equipt with enough light collecting cells in our eyes or specialist systems like cats have for us us to see well in low light conditions.
Interesting consideration, Michael.
But my question was different: why it is physically dark in the night? Why there is (almost) no light, or much less light in the night than during the day?
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Offline kalimna

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Re: Question of the Week - Old Version
« Reply #370 on: 15/12/2006 18:20:28 »
And Im guessing that your answer has little to do with the fact  that of all the photons streaming from the sun (primary source of 'light' received by the earth), at night they are only interacting with the side facing the sun? And hence the side away from the sun is receiving only starlight (and reflected sunlight from the moon)....
Or am I missing something here?
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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #371 on: 16/12/2006 13:39:05 »
And Im guessing that your answer has little to do with the fact  that of all the photons streaming from the sun (primary source of 'light' received by the earth), at night they are only interacting with the side facing the sun? And hence the side away from the sun is receiving only starlight (and reflected sunlight from the moon)....
Or am I missing something here?

You don't miss anything, the answer has nothing to do with that.

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Offline kalimna

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Re: Question of the Week - Old Version
« Reply #372 on: 16/12/2006 15:09:49 »
Hmmm, well in that case, Im stumped! Unless the answer is one of those metaphysical philosophising answers. 'Why is it dark?' - 'Because it is not light'.......
Throw us a bone here :)

Adam
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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #373 on: 17/12/2006 14:44:40 »
Hmmm, well in that case, Im stumped! Unless the answer is one of those metaphysical philosophising answers. 'Why is it dark?' - 'Because it is not light'.......
Throw us a bone here
:)

Ok. The bonus is:
star's light.

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Offline Soul Surfer

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Re: Question of the Week - Old Version
« Reply #374 on: 07/02/2007 10:04:05 »
Just latched on to this I think he is talking about "Olbers paradox"  If the universe was infinite every line of sight would end up on a star and it would be uniformly bright.  The fact that it is dark at night means that the universe is finite in space time or both.

It is also essential for life to work to have a heat flow so a uniform high temperature universe without light or dark bits would be boring and devoid of life.
« Last Edit: 07/02/2007 10:05:39 by Soul Surfer »
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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #375 on: 07/02/2007 12:00:17 »
A winner! At last! Cheers!

The Wiki explanation, however, is focused more on the universe's expansion, and the consequent Doppler redshift of light from distant stars (frequency and intensity becomes lower and lower with distance).


http://en.wikipedia.org/wiki/Olber%27s_paradox

So, folks, the night is dark Because of the Big Bang!
« Last Edit: 07/02/2007 12:15:12 by lightarrow »

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jolly

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Re: Question of the Week - Old Version
« Reply #376 on: 24/02/2007 19:12:30 »
i guess its because as your skin gets cold it shrinks, as all things do, and as it shirks it makes little hills with air between them which helps them retain heat when used in conjuction with the bodies hairs, the bodies heat then has to travel up through these little hills as if theres extra skin there. so it could be like the body gives itself an extra two or three layers of skin slowing down heat loss; and keeping you warmer just long enought for you to find a jumper.lol best guess why is it?

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jolly

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Re: Question of the Week - Old Version
« Reply #377 on: 24/02/2007 19:13:55 »
sorry answered without realising it had finished.

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #378 on: 04/04/2007 17:00:29 »
QUESTION: WHAT IS THE SPEED OF GRAVITY?
Steven
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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #379 on: 04/04/2007 19:32:34 »
QUESTION: WHAT IS THE SPEED OF GRAVITY?
C

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #380 on: 04/04/2007 19:50:06 »
Einstein extracted a wave equation from his theory of general relativity that does state that gravity would travel at approximately 186,000 miles a second or "C". To my knowledge though, this hasn't been demonstrated.
Steven
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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #381 on: 05/04/2007 08:05:52 »
Einstein extracted a wave equation from his theory of general relativity that does state that gravity would travel at approximately 186,000 miles a second or "C". To my knowledge though, this hasn't been demonstrated.
Do you mean experimentally? Of course not, since, AFAIK, gravitational waves hasn't been even detected yet.
« Last Edit: 05/04/2007 13:23:56 by lightarrow »

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #382 on: 05/04/2007 12:28:11 »
Yes I meant experimentally.
Steven
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lyner

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Re: Question of the Week - Old Version
« Reply #383 on: 15/04/2007 16:58:17 »
As a measurement exercise, it is a nightmare. There is so much 'gravitational interference' from every other mass in the universe. The waves are expected to be very small and v e r y  l o w  f r e q u e n c y. If they were easy to spot, we would have seen them already.
If you could get near a large binary star system, orbiting around its centre  of mass,  or a couple of black holes interfering with each other, - better, still , a  supernova in our back yard, you would be in a better position to detect these waves (if, of course, they exist).
The LIGO   (Laser Interferometer Gravitational-Wave Observatory) is hoping to detect gravitational waves by tiny amounts of movement between mirrors situated on the Earth and spaced by a few km.  LISA (Laser interferometer space antenna) is planned in the fairly near future, which will detect the relative wobbling of a set of satellites  - spaced by a few million km - as gravitational waves go past.
Nothing to report yet but keep your fingers crossed and avoid slamming doors and general loud behaviour; that realy doesn't help the sensitive equipment.

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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #384 on: 16/04/2007 12:24:27 »
[...]
Nothing to report yet but keep your fingers crossed and avoid slamming doors and general loud behaviour; that realy doesn't help the sensitive equipment.
Yes. I have never been able to understand how they can remove the error due to all the tiny earthquakes there are constantly in our planet.

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lyner

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Re: Question of the Week - Old Version
« Reply #385 on: 18/04/2007 09:39:21 »
There would be some directivity in the sensitivity of the measuring array, presumably. You could avoid Interference from Earth by looking 'tangentially', perhaps, and then pick your moments for measurement when you are not pointing at anything too close and 'noisy'.
That's the technique for radio astronomy, after all, when your telescope is not steerable.
I would like to know the effective 'beamwidth' of the detector; it could be pretty narrow in the case of the LISA system, because of the enormous aperture. LIGO is not that big, however. Just a lot less sensitive, I would guess.

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jolly

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Re: Question of the Week - Old Version
« Reply #386 on: 28/04/2007 01:51:30 »
Sorry thats a silly question.
Gravity does not have a speed.
What are you really asking? Earth gravity I suppose your talking about. It depends on the mass, different masses are affected differently.
The speed of an object affected by earths gravity?
Gravity itself doesnt have a speed its a force- Not like light which is radiation and has a speed of sorts.
The question makes no sense.
I mean black holes are the strongest gravity zones so are you asking a what speed are you pulled into them? because that again depends on the blackholes size.
Are you asking at what speed you travel around blackholes- our sun travels about 42,000 miles an hour around our milky ways super massive black hole.
But your question is about gravities speed and really it does not have a speed- In my opinion!

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #387 on: 28/04/2007 01:57:28 »
If the sun disapeared we wouldn't instantly verge off out of orbit. This means gravity isn't instant. Saying "Sorry thats a silly question" isn't helping the discussion.
Steven
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jolly

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Re: Question of the Week - Old Version
« Reply #388 on: 28/04/2007 12:14:55 »
If the sun disapeared we wouldn't instantly verge off out of orbit. This means gravity isn't instant. Saying "Sorry thats a silly question" isn't helping the discussion.

How is that exactly- there would be no orbit if the sun disapeared- and you would verge off- actually. Gravity is a constent and therefore always affects things with in it arena- instantly. So what are you asking? If the sun disapeared how quickly will we be influenced by another star? answer is straight away.

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #389 on: 28/04/2007 14:02:04 »
If the sun disapeared we wouldn't instantly verge off out of orbit. This means gravity isn't instant. Saying "Sorry thats a silly question" isn't helping the discussion.

How is that exactly- there would be no orbit if the sun disapeared- and you would verge off- actually. Gravity is a constent and therefore always affects things with in it arena- instantly. So what are you asking? If the sun disapeared how quickly will we be influenced by another star? answer is straight away.

Sorry what I mean to say was "If the sun disapeared we wouldn't instantly verge off out of orbit instanly". It would verge off but not instantly." If you disagree with that you are wrong.
Steven
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jolly

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Re: Question of the Week - Old Version
« Reply #390 on: 28/04/2007 16:04:01 »
Hello, if the sun disappeared there would be nothing to orbit.
We would stop and go somewhere else- straight away. All the planets would fly off in the same direction. As the gravity from either the super massive blackhole at the milky ways core or a closer star would pull us in.
What are you getting at that our speed and direction would remain the same for a while after the sun disappeared- that is totally un-true. The secound the sun disappeared the earth and other planets would pull towards the next high gravity source.
So what you planning- Gonna destroy the sun as part of some stupid experiment, to see if your ideas are correct- Thats inteligent.

Even if you did fly off in the same dirrection for a while the gravity from near by stars would have an affect on you and slow you down.
Gravity has no speed- It is intentanious- As its always there.
« Last Edit: 28/04/2007 16:08:45 by jolly »

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #391 on: 28/04/2007 16:19:49 »
I disagree.
Steven
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Offline i am bored

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Re: Question of the Week - Old Version
« Reply #392 on: 28/04/2007 18:19:15 »
QUESTION: WHAT IS THE SPEED OF GRAVITY?
  9.8 m/s^2
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Offline lightarrow

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Re: Question of the Week - Old Version
« Reply #393 on: 28/04/2007 19:43:56 »
Hello, if the sun disappeared there would be nothing to orbit.
Yes, but when? If the sun moved, clearly orbits should vary as well. Let's say that the sun suddenly moves at 00:00. When will the planets feel this variation? Not immediately, because that "information" cannot travel faster than light's speed. According to Einstein's general relativity, it travels exactly at light's speed, indeed.

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jolly

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Re: Question of the Week - Old Version
« Reply #394 on: 29/04/2007 11:57:09 »
Yes, but when? If the sun moved, clearly orbits should vary as well.

The sun is always moving around the milkly way at about 42,000 mph. and the orbits are affected to a degree.

Let's say that the sun suddenly moves at 00:00.
So what are you saying 'lets say the sun just stopped moving'- Not gonna happen thats impossible.

When will the planets feel this variation? Not immediately, because that "information" cannot travel faster than light's speed. According to Einstein's general relativity, it travels exactly at light's speed, indeed.
Right the affects of the super massive black hole at the center of the milkly way are felt throughtout our galaxcy- and beyond, as the next closest galaxcy is currently pulling towards us.
Gravity is a constent- in other words it is just there- immediate- It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.
We are all caught with-in gravity; and the affect of gravity- will be instentaniuos as a result. Gravity is nothing like light. Once in position- its there- and as a result you will feel the affects straight away.
Kinda like a spiders web.
Light is radiation- Gravity is a force, Gravity once it has formed this spiders web- ergo, the area of its influence. will affect the things with-in its grasp straight away- and under those circumstances it has no speed it will be felt straight away.


:-Because that "information" cannot travel faster than light

Since when is matter- information.
« Last Edit: 29/04/2007 12:07:11 by jolly »

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Offline rosy

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Re: Question of the Week - Old Version
« Reply #395 on: 29/04/2007 12:29:01 »
Nic- the "speed of gravity" being discussed here is the speed at which the effect of gravity propagates through space. It has been suggested (derived from the maths) that this occurs at the speed of light (3x108 ms-1), but this hasn't been experimentally demonstrated (even assuming it's true this would be unsurprising since the experiments are a total nightmare due to the amount of competition from noise).
9.8 ms-2 is the rate of acceleration due to gravity at the earth's surface, but the magnitude of that is due to the mass of the earth. On the moon it's about 1/6 of that value.

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another_someone

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Re: Question of the Week - Old Version
« Reply #396 on: 29/04/2007 15:43:06 »
Gravity is a constent- in other words it is just there- immediate-

Constant and immediate are not the same thing (a DC current in a wire is constant, but it still has a speed through the wire).

It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics (if the effects of the Sun's gravity were to take 8 minutes to reach the Earth when it was first formed, but instantly disappears when the Sun disappears, then the Earth will have experienced the gravity of the Sun for 8 minutes less than the Sun was actually producing gravity - thus if there is a time lag in the effect of an increase of gravity, then there should be a similar time lag in it diminishing).

Light is radiation- Gravity is a force

The difference is not as much as you indicate.

Light is merely a manifestation of the coulomb force (i.e. the force of an electric field).  We perceive light as a wave because of the finite speed at which the coulomb force travels, and the effects of General Relativity upon the coulomb force emanating from a moving electrically charged particle (as one would have from the electrons moving in a piece of wire under the effect of an electric voltage applied to the wire).

:-Because that "information" cannot travel faster than light

Since when is matter- information.

Gravity does carry information, just as an electric field carries information.

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon.  In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans.  Thus, if gravity was instantaneous, then this information would be received by us instantaneously.
« Last Edit: 29/04/2007 16:17:34 by another_someone »

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Offline Mjhavok

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Re: Question of the Week - Old Version
« Reply #397 on: 29/04/2007 16:15:15 »
It makes me happy when George answers.
Steven
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jolly

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Re: Question of the Week - Old Version
« Reply #398 on: 29/04/2007 22:02:43 »
Gravity is a constent- in other words it is just there- immediate-

Constant and immediate are not the same thing (a DC current in a wire is constant, but it still has a speed through the wire).

That is only true while the electric applience is being used.

Gravity is a constent- in other words it is just there- immediate-
It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics

Right yes, it may take a while to reach its full area of influence- but how are you going to find out what that speed is; because you are currently trapped with-in that area of influence- that is not just our sun but also the other stars and the supermassive black hole at our galaxys core. Even if you remove the sun- the others still affect you instantly. In other words it really does not matter how long it took to create it full area of influence- As once formed it will affect everything with-in its area of influence instentaiously.

Gravity is a constent- in other words it is just there- immediate-

Constant and immediate are not the same thing (a DC current in a wire is constant, but it still has a speed through the wire).

It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon.  In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans.  Thus, if gravity was instantaneous, then this information would be received by us instantaneously.

O.k you cannot do that the information you talk about is really an effect you see happening as a result of gravities affect on something- But you percieve that; it may be that you think something has been caused by gravity when it has not or that the affect was so small you did'nt notice. Whatever you look at will be affected by all the different gravity sourses around it, which will make the thing you look at, act differently- so until you can identify all of the different gravity sourses and how they affect something inseperation- how can you know.

The trouble here is at the moment you cant- As all the different gravity influences are jumbbled up togther and we do not have the understanding or technology to see them in isolation- any assertion will simply be a best guess.
   
Just because you do not notice an affect does not mean you are not being affected-
e.g the plane thats lost it engine and is flying free- the passengers may not notice that they are glyding.
"honey, the ground is getting very close all a sudden" "stop worrying dear the pilot knows what he's doing" BANG

So as I said before we are under gravities influence and in that situation, its affect will be instentanious- ergo gravity has no speed.

on the creation of a new black hole you could look to see how quickly the things around it are affected- but you would need to add into that equation what other gravities are affecting those things near it as they may speed up or slow the black holes visual affects. 
« Last Edit: 29/04/2007 23:03:20 by jolly »

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another_someone

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Re: Question of the Week - Old Version
« Reply #399 on: 30/04/2007 03:17:44 »
Constant and immediate are not the same thing (a DC current in a wire is constant, but it still has a speed through the wire).

That is only true while the electric applience is being used.

Nothing to do with appliances - if I connect a wire from the positive terminal of a battery to the negative terminal of the same battery, a DC current will flow along that wire.

Gravity is a constent- in other words it is just there- immediate-
It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics

Right yes, it may take a while to reach its full area of influence- but how are you going to find out what that speed is; because you are currently trapped with-in that area of influence-

You don't need to observe its impact upon you (in any event, one cannot judge speed by looking at one location - one must observe at least two locations).  Thus, if you observe the impact of changes in gravity upon two or more other bodies that are separated by a distance, you can tell if a change in gravity effects both objects at the same time, or it effects one object before the other.

In other words it really does not matter how long it took to create it full area of influence- As once formed it will affect everything with-in its area of influence instentaiously.

But you have not explained, if there is a delay in gravity reaching you when it is being 'formed', why that same delay should not exist when the gravity is being destroyed?

In your world, one could get the rather perverse situation where you detect the loss of a  gravitational field before you detect the existence of a gravitational field (because the detection of the creation of the gravitational field took a finite time to reach you, but the collapse of the gravitational field arrived instantaneously).

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon.  In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans.  Thus, if gravity was instantaneous, then this information would be received by us instantaneously.

O.k you cannot do that the information you talk about is really an effect you see happening as a result of gravities affect on something- But you percieve that; it may be that you think something has been caused by gravity when it has not or that the affect was so small you did'nt notice. Whatever you look at will be affected by all the different gravity sourses around it, which will make the thing you look at, act differently- so until you can identify all of the different gravity sourses and how they affect something inseperation- how can you know.

The trouble here is at the moment you cant- As all the different gravity influences are jumbbled up togther and we do not have the understanding or technology to see them in isolation- any assertion will simply be a best guess.
   
Just because you do not notice an affect does not mean you are not being affected-
e.g the plane thats lost it engine and is flying free- the passengers may not notice that they are glyding.
"honey, the ground is getting very close all a sudden" "stop worrying dear the pilot knows what he's doing" BANG

So as I said before we are under gravities influence and in that situation, its affect will be instentanious- ergo gravity has no speed.

on the creation of a new black hole you could look to see how quickly the things around it are affected- but you would need to add into that equation what other gravities are affecting those things near it as they may speed up or slow the black holes visual affects. 


If one takes a solipsistic approach, one can never actually prove anything beyond one's own mere existence; but in practical terms, there is overwhelming evidence that the tides are caused predominantly my the pull of the moon upon the Earth.  You are correct that other bodies also have an influence, but the tides are so obviously synchronised to the orbit of the moon, and there is nothing else which is synchronised to the same extent with the ebb and flow of the tides, that I think we can regard it as highly improbable that the dominant force exerted upon the tides emanates from the Moon.