# The Physics Thread 115 replies

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random_soldier1337

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#1 10 years ago

So I'm like a Physics geek and stuff and I wanted to create a thread to discuss Physics oriented stuff ("Physics geeks unite!"). I guess it could be used for universal Physics needs on filefront, provided it survives that long. Otherwise,...whatever. I'm currently studying relativity in my class and I was studying about time dilation. The fact that time is relative and that time is different from all different perspectives and all frames of reference, is this the fact that leads to the idea of there being several different universes? I thought about this but then I remembered that it is a dimension used for measuring the universe we live in just as the x,y and z coordinates are. So I'm sort of wondering where this idea of time travel and several different universes originates from because this does lead to some sort of confusion especially since the time dilation effect defies what would be referred to as "common-sense". Also, just a minor question but what is the Lorentz Factor supposed to be? Is it like a constant or a value that measures something(s) or what? The explanation on Wikipedia doesn't seem to make sense and the best guess I can make is that it is a constant, in the case of time dilation, and for a given relative velocity it can be used to measure the time dilation for the observer for a given period of the proper time.

MrFancypants Forum Admin

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#2 10 years ago

The Lorentz factor is not a constant, it is a factor used to determine the effects of the speed of an object on an observer.

If you insert a low speed you'll see that because of the equation the factor will be close to one, so there isn't much of a time dilation/mass effect/length contradiction. If you get closer to the speed of light the factor becomes larger than one, so the effects increase. The factor describes the way in which the effects increase over an increase of velocity.

random_soldier1337

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#3 10 years ago

Okay. Thanks. New question. (hypothetical situation) Say if there is a passenger on a bullet train travelling at 0.482c and he drops a shiny stainless steel ball bearing of radius 0.0125 m through a height of 1.36 m, what would be the time measured for the drop of the ball bearing by the passenger and by a stationary observer outside? I've determined 0.527 s by the passenger and 0.601 s by the observer. Though my real question is, would the radius of the ball bearing be of any relevance? I think it's a something to throw a person off but I'm not sure because often I make a mistake thinking a value is irrelevant. Also if everything was the same as in the previous case but it was the stationary observer that dropped the ball bearing instead of the passenger, wouldn't the proper time and the dilated time be reversed i.e. the stationary observer would observe the ball bearing to drop for 0.527 s and the passenger observe it drop for 0.601 s? My thinking is that because from a certain perspective it could be said that the passenger is the stationary observer and the stationary observer is the person who is moving by really fast, right?

Nittany Tiger Forum Mod

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#4 10 years ago
Siddharth Gupta;4787281Though my real question is, would the radius of the ball bearing be of any relevance? I think it's a something to throw a person off but I'm not sure because often I make a mistake thinking a value is irrelevant.

In this case, no. 2.15 mm is small compared to 1.36m.

Also if everything was the same as in the previous case but it was the stationary observer that dropped the ball bearing instead of the passenger, wouldn't the proper time and the dilated time be reversed i.e. the stationary observer would observe the ball bearing to drop for 0.527 s and the passenger observe it drop for 0.601 s? My thinking is that because from a certain perspective it could be said that the passenger is the stationary observer and the stationary observer is the person who is moving by really fast, right?

I don't think so, though you can do coordinate transforms (the name for the relativity version is on the tip of my tongue at the moment) to be sure. Just do it for time.

And is all physics game in this thread?

MrFancypants Forum Admin

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#5 10 years ago

Now don't drop your homework on me, its been a couple of years since I had to do that kind of stuff ;)

0.527 and 0.601 seems to be right. Maybe your teacher wanted you to think about length contraction, but I think length contraction only occurs in direction of the movement of the intertial system.

Also, the observer has either damn good eyes or will be sucked into the train if he tries to get close enough to observe such a small ball bearing (if Bernoulli has to say anything here, at least).

As for reverseing the situations, I think in that case you have to use the inverse of the Lorentz-factor, but as I said, it has been a while.

Captain Fist

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#6 10 years ago

I hate math.

random_soldier1337

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#7 10 years ago
Killer Kyle;4787302In this case, no. 2.15 mm is small compared to 1.36m.[/quote] Umm... actually that's 12.5 mm...
Killer Kyle;4787302I don't think so, though you can do coordinate transforms (the name for the relativity version is on the tip of my tongue at the moment) to be sure. Just do it for time.[/quote] Could you clarify though? The relative velocities between the 2 moving objects remains the same so it only matters who is dropping the ball bearing, in which case the person dropping the ball bearing is the stationary person and has the proper time. At least that's how far my thinking goes. Sorry, I'm not sure I understand what you mean.
Killer Kyle;4787302And is all physics game in this thread?[/quote] Wait, what what do you mean "Physics game"? I made this thread to discuss anything physics related. As long as it's actually real-world physics or physics that presents real-world/similar to real world situations (or relatively, given how absurd my question is with a guy being able to see a ball bearing on a bullet train moving at nearly half the speed of light:lol:). EDIT: I mean it can be anything physics related as long as the rationales are derived from actual physics explanations/calculations/laws,etc.
MrFancypants;4787309Now don't drop your homework on me, its been a couple of years since I had to do that kind of stuff ;) 0.527 and 0.601 seems to be right. Maybe your teacher wanted you to think about length contraction, but I think length contraction only occurs in direction of the movement of the intertial system.
Sorry about that. I just thought the values would be of some help. Basically all I wanted to ask was would the times be measured simply be reversed if it was the other person dropping the ball bearing or would there be some difference by calculation or another method. [quote=MrFancypants;4787309]Also, the observer has either damn good eyes or will be sucked into the train if he tries to get close enough to observe such a small ball bearing (if Bernoulli has to say anything here, at least).
That's why I said the situation was hypothetical. ;) [quote=MrFancypants;4787309]As for reverseing the situations, I think in that case you have to use the inverse of the Lorentz-factor, but as I said, it has been a while.
But... that would mean that time would be accelerated rather than dilated for the person who is observing the ball bearing being dropped. Is that supposed to happen? I think I might have misunderstood "inverse" of the lorentz factor. [quote=Ihaterednecks;4787342]I hate math.

Then what are you doing here?

Captain Fist

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#8 10 years ago
Then what are you doing here?

Commenting.

Nittany Tiger Forum Mod

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#9 10 years ago

Siddharth Gupta;4787350Umm... actually that's 12.5 mm...

Could you clarify though? The relative velocities between the 2 moving objects remains the same so it only matters who is dropping the ball bearing, in which case the person dropping the ball bearing is the stationary person and has the proper time. At least that's how far my thinking goes. Sorry, I'm not sure I understand what you mean.

Sorry about that. I haven't been good with in-head conversions for quite a while.

I'm not sure if you mathematically perform the Lorentz transforms (That's what I was talking about earlier that I couldn't remember) on the times that you will get the reversal that you think will occur. I'll think about it and/or do the math later.

Wait, what what do you mean "Physics game"? I made this thread to discuss anything physics related.

You misread the sentence. When I said "Is all Physics game?," I was asking if all anything physics related ok for this topic (from classical mechanic to particle theory and everything else).

But you already answered my question in the edit.

Danger: If I get back into grad school, expect fluid dynamics discussion because that was never covered for my major as an undergrad, and I need to learn some now. Reason: I'm now a meteorology major, and they rely heavily on fluid physics.

random_soldier1337

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#10 10 years ago

All right. No problem. "All physics is game" as you would put it (can't believe I forgot that expression:p).