Physics talk

[imdying]

and the built in fudge factor by the us military which changes day to day

That was turned off over a decade ago; accuracy is no longer degraded at all.

/edit: Here you go http://en.wikipedia.org/wiki/Selecti...e_availability

[Akzle]

i'm going to re-link this here. cos it's cool.

http://htwins.net/scale2/

[Ocean1]

and distance? I thought it was only subjective time that changed, or do you mean the ship stretches out as it approaches light speed?

It does. In fact if you ignore just the impossibility of actually observing it an object falling into a black hole would appear to stretch and stall, never actually reaching the event horizon.

Edit: in fact the ocupants would be in serious trouble from the same problem but different reason: they'd be torn apart by the variable gravity over the length of their body.

[bogan]

It does. In fact if you ignore just the impossibility of actually observing it an object falling into a black hole would appear to stretch and stall, never actually reaching the event horizon.

Edit: in fact the ocupants would be in serious trouble from the same problem but different reason: they'd be torn apart by the variable gravity over the length of their body.

Yeh, just when he said distance it sounds more like the distance travelled by the ship, rather than the ships length changing.

You would get massive red or blue shift at the point though, and it'd probably just fade out due to the time differential effecting the light emissions, actually, it would probably fade out going through the spectrum (i think it'd be blue shift).

Do the occupants stretch that much? isn't it only the viewer perception of them that gets stretched.

[p.dath]

Centrifugal growth can cause tyre diameter to increase 2% on a steel belt and more on older tyre.
At slow speeds inflation pressures can change the distance travelled per rotation also.
A under inflated tyre will cover less distance at slower speeds but will grow taller than a correctly inflated tyre at high speeds.
They are only small amounts.

The same goes for a gearbox driven speedo. As the bike gets faster the percentage of wheel slip increases and the speedo reads faster than true speed travelled. Some bike racing on salt lakes travelling 300 have a rear wheel speed of 330+ losing 30kph or more in wheel spin.

These are all small factors when riding a bike and wouldnt be enough to make a difference at road legal speeds though.

It's worse than that. Often different parts of a tyre spin a different speeds - which is related to tyre deformation. The effect is most pronounced when accelerating, braking, or when experiencing lateral force on the tyre.


Here is another one that I had trouble with initially. For a tyre to rotate, it has to slip. So at any point in time you are riding, you tyres *are* slipping. And as you cross the point of coming off, all that has happened is the slip has exceed the grip. Once you come to the understanding that moving tyres are permanently slipping you start to take on a different appreciation of how they work.

[imdying]

For a tyre to rotate, it has to slip.

To rotate, or to change speed of rotation?

[Dave-]

Proof please.

There's lots of material out there because it was published by Einstein

Is the speed of light, a photon's terminal velocity though?

Just occured to me and it's too hard to edit posts from my phone.

Yes, or so the current belief lies, I think there was some talk a wee while ago in quantum about a sub atomic particle that slows down as it reaches the speed of light or something hilariously weird like that.

and distance? I thought it was only subjective time that changed, or do you mean the ship stretches out as it approaches light speed?

So the length contraction is relative to the position of the observer, if you're on a spaceship doing 0.8c things look shorter to you, if you're on a stationary space ship and one goes by you at 0.8c then it's stretched.

I think. I can't remember and my level 1 physics text book is buried at the bottom of a box under a bunch of other boxes.

For anyone interested the twin paradox is quite a good read:

"If we placed a living organism in a box ... one could arrange that the organism, after any arbitrary lengthy flight, could be returned to its original spot in a scarcely altered condition, while corresponding organisms which had remained in their original positions had already long since given way to new generations. For the moving organism, the lengthy time of the journey was a mere instant, provided the motion took place with approximately the speed of light." - Albert Einstein

Explained in a bit more plain english:

"If the stationary organism is a man and the traveling one is his twin, then the traveler returns home to find his twin brother much aged compared to himself. The paradox centers around the contention that, in relativity, either twin could regard the other as the traveler, in which case each should find the other younger—a logical contradiction. This contention assumes that the twins' situations are symmetrical and interchangeable, an assumption that is not correct. Furthermore, the accessible experiments have been done and support Einstein's prediction. ..." - Robert Resnick

http://en.wikipedia.org/wiki/Twin_paradox

Also interesting is the Helios Probes, which hold the record for the fastest man made objects
http://en.wikipedia.org/wiki/Helios_(spacecraft)

The Helios probes got up to 252,792 km/h which is pretty fuckin' fast, that's around the equator in about 10 minutes.

speed of light is 1.079x10^9 (a billion kilometers per hour) so the fastest man made objects have achieved about 0.02% the speed of light....aka....fuck all.

[bogan]

Here is another one that I had trouble with initially. For a tyre to rotate, it has to slip. So at any point in time you are riding, you tyres *are* slipping. And as you cross the point of coming off, all that has happened is the slip has exceed the grip. Once you come to the understanding that moving tyres are permanently slipping you start to take on a different appreciation of how they work.

You mean that the different parts of the contact patch are 'slipping' in different directions so it can sit flat on the road, with a net slip of 0? Or that it is always slipping a tiny tiny bit?

[pzkpfw]

and distance? I thought it was only subjective time that changed, or do you mean the ship stretches out as it approaches light speed?

Distance also changes. You don't see yourself change, but if you go very very fast, another observer will see you get shorter, in the direction of travel. You will "see" the Universe getting shorter.

You'll have heard that if you went "very very fast" to the next star over, that you'd think less time had elapsed than someone left behind would think. Well, you'd also have travelled what was to you a shorter distance than that person back home would measure.

http://en.wikipedia.org/wiki/Length_contraction


Edit: Darn you Dave-, and your fast typing.

[Dave-]

Distance also changes. You don't see yourself change, but if you go very very fast, another observer will see you get shorter, in the direction of travel. You will "see" the Universe getting shorter.

You'll have heard that if you went "very very fast" to the next star over, that you'd think less time had elapsed than someone left behind would think. Well, you'd also have travelled what was to you a shorter distance than that person back home would measure.

http://en.wikipedia.org/wiki/Length_contraction


Edit: Darn you Dave-, and your fast typing.

interestingly though because the stars are so massively hugely far apart, even compared to the speed of light, the distance between the points barely changes.

So at the speed of light the stars don't streak through the sky all awesomely....they just sort of sit there going "you're only going the speed of light, it's still going to take you 4000 years to get here...."

[bogan]

Distance also changes. You don't see yourself change, but if you go very very fast, another observer will see you get shorter, in the direction of travel. You will "see" the Universe getting shorter.

You'll have heard that if you went "very very fast" to the next star over, that you'd think less time had elapsed than someone left behind would think. Well, you'd also have travelled what was to you a shorter distance than that person back home would measure.

http://en.wikipedia.org/wiki/Length_contraction


Edit: Darn you Dave-, and your fast typing.

Won't the observer see you get longer? Cos if your distance to the star gets shorter, the meter ruler on the ship has to get longer right? It all makes sense, it just seems more like a secondary effect of the time dilation than a phenomenon in itself.

[schrodingers cat]

There's lots of material out there because it was published by Einstein

I'm afraid I can't allow that answer Dave.

Thus far ACTUAL behaviour at the speed of light has not been proved.

Please refrain from confusing yourself further

[Dave-]

I'm afraid I can't allow that answer Dave.

Thus far ACTUAL behaviour at the speed of light has not been proved.

Please refrain from confusing yourself further

Yeah you're right, we wont know for sure until we do it.

And we won't come even close to achieving this until we stop waring with each other.

edit: was that a 2001 space odyssey reference there too?

[Ocean1]

Yeh, just when he said distance it sounds more like the distance travelled by the ship, rather than the ships length changing.

You would get massive red or blue shift at the point though, and it'd probably just fade out due to the time differential effecting the light emissions, actually, it would probably fade out going through the spectrum (i think it'd be blue shift).

Do the occupants stretch that much? isn't it only the viewer perception of them that gets stretched.

From their perspective frequency shift is irrelevant. And the difference in gravity over even 1m is enough to tear anything that large appart close to an event horizon.

And not even very close.

[MisterD]

Rock fan-dom was definitely over represented on my Physics degree course.