Infinite acceleration?!

[Verthanthi]

Originally posted by poop juice
its surprising how often things people are "certain" about turn out to be wrong

You didn't answer my question. Are you saying that an object can never have a velocity of 0? That would be my definition of at rest. And unless you're trying to apply Heisenberg's Uncertantiy Principle or you're playing with reference frames, yes object can come to rest.

While it's true that you can always find a reference frame where the object I claim is at rest is moving, I can also find a reference frame where any object you claim is moving is at rest. So don't waste our time with doing that. The uncertantity principle (from my admittedly light understanding of it) is only meaningful for subatomic particles, so that's also fairly irrelevant.

However, if you're saying that having v=0 doesn't constitute rest, or that objects can never have v=0, I'd by all means like to see your definition/proof.

[EternalEntropy]

Originally posted by Verthanthi
You didn't answer my question. Are you saying that an object can never have a velocity of 0? That would be my definition of at rest. And unless you're trying to apply Heisenberg's Uncertantiy Principle or you're playing with reference frames, yes object can come to rest.

While it's true that you can always find a reference frame where the object I claim is at rest is moving, I can also find a reference frame where any object you claim is moving is at rest. So don't waste our time with doing that. The uncertantity principle (from my admittedly light understanding of it) is only meaningful for subatomic particles, so that's also fairly irrelevant.

However, if you're saying that having v=0 doesn't constitute rest, or that objects can never have v=0, I'd by all means like to see your definition/proof.

Also on a side note there is no such thing as an absolute zero velocity. There is relative zero velocity but there is always *some* kind of motion. You wouldnt even know what direction to fly in achieve no velocity because velocity is always relative to something. Take for instance the motion of the earth around the sun, you would need to counteract this to achieve zero velocity relative to the sun. You will notice the sun is moving in space also, so you would need to figure out zero velocity in comparison to the center of the milky way (most likely a black hole). Unfortunately galaxies also move in relativity to each other and so you would need to figure out what the center of the universe is (?) and achieve a zero velocity with that. Beyond that is anybody's guess but I wont go there. Also there is the movement of the atoms themselves. Unless at zero kelvin (thought to be impossible to reach) atoms will always be in motion.

[Da1andonly]

Lol this reminds me of philosohpy...dunno what these were called..something like palindromes =P

If you shoot an arrow towards a screen, it shouldn't get there.
Why? Because when you shoot the arrow, it has to be on a specific place EVERY millisecond right? And in order to be on a specific place, the arrow has to stand still. If it moves, it's not on a specific place. So when you shoot it, it stands "still", cause it's on a specific place, but still it reaches the target. Impossible

[pv=nrt]

Eternal, I disagree about the atoms at zero kelvin. At that themperature the atoms would be moving so slow they would appear to be still, while actually still moving. I think I remember seeing something about researchers getting down into the 5 K range, but that may be my mind playing tricks on me.

[geekbot]

Re: Re: Infinite acceleration?!

EternalEntropy is smrat.

There is something wrong with the statement "Whenever anything moves from rest it must have infinite acceleration." There is no difference between going from 0 m/s to 1 m/s and going from 2 m/s to 3 m/s. See here's a graph:

velocity
    |
    |
 \  |
  \ |
   \|
__________________ time
    |\
    | \
    |  \
    |   \
    |    \
    |     \
    |      \

Here a constant acceleration is applied. See, the velocity is decreasing (change in velocity = acceleration) which means the object is slowing down. At time=0, it velocity is 0 and the object starts moving backwards. A nice straight line that doesn't change, bend...velocity goes through zero and the acceleration was constant (constant is not infinity). No calculus required.

If you want to the case where the object starts at rest, erase the part before time=0.

[Da1andonly]

What's zero kelvin? -271'something degrees celsius?

If it is, the atoms aren't moving at all, cause that's the absolute "zerospot", everything is frozen down.

If it isn't, excuse me

[TelC@t]

Originally posted by wadi
I assumed he was reffering to the fact that in a perfectly elastic "hard"(no warping of either object or wall) collision, an object moves from x velocity to x velocity in the opposite direction over time approaches 0 giving it infinite acceleration.

Gosh u suck at physics

In the case you have stated, the object travels towards the wall at velocity x will have to come to a stop first before it starts to travel in the opposite direction. So unless it is feasible for an object to go from velocity x to 0 velocity in 0 secs, it is not possible to have infinite acceleration.

So basically you assumed a scenerio where an object can undergo a deceleration from velocity x to 0 velocity 0 secs and then acelerate from 0 velocity to velocity x in 0 seconds.

[!cER]

Re: Infinite Acceleration

I'm confused as why it must have infinite acceleration. Have you taken any calc?

In the first instant an object moves from rest t=0, and it moves some distance (if it didnt move any didnt move any distance then the time wouldnt equal zero). Therefore the acceleration which is change is distance divided by change in time is a distance divided by zero which is infinite. This also applies when the object chnges direction as it has to stationary at one instant in time.

Anyway, for objects turning around, the object does come to rest for a small amount of time, but the time is very small.

However I think the answer is something similar to what Fit of Rage said:

If you're dividing by zero, it's not infinite. It's undefined. Remember 7th grade Algebra? Think back.

As both time and distance are continuous they should reach zero and the same time, and therefore you get 0/0 which is undefined and can be whatever you want. However there is a problem with this :/. If it doesnt move at all in the first instant it hasnt accelerated and is still at rest, so the problem is just delayed. I guess the answer is just that you cant get 0 time, but im still unsure (this was all only hypothetical anyway)

Btw the definition of absolute zero is when the atoms stop moving, but it probably is unreachable.

[Sleepy Weasel]

Re: Re: Infinite Acceleration

Originally posted by !cER
In the first instant an object moves from rest t=0

Except it's not, t is small, but not 0.


Basically you're asking this question:

Originally posted by za gophar
if you shoot an arrow at a target, the arrow must go halfway. once it gets halfway, it must go half of the remaining distance. then it goes half of THAT remaining distance. if keeps on cutting the remaining distance in half... but how the hell does it hit the target? IN FACT, how could the arrow even begin to move? in order for it to get halfway to the target at all, it must get a fourth of the way first.. and so on....

That was raised in this thread:
http://forums.trenchwars.org/showthr...&threadid=4468

but phrasing it in a different way. It's just limits.

[Sleepy Weasel]

Re: Re: Infinite Acceleration

Originally posted by !cER
Therefore the acceleration which is change is distance divided by change in time is a distance divided by zero which is infinite.

Actually velocity is change in distance/change in time, dx/dt. Acceleration is change in velocity over time, the second derivative. And yes your time is very very close to 0 at the initial movement, but the distance is also very very close to 0, so there is nothing remotely close to infinite acceleration about it. If there is movement, time has passed. If time is 0, there has been no movement yet and therefore no velocity yet. Just because we don't really perceive stuff that happens much quicker than say .1 seconds, you can't say something that happens in .00001 seconds happened in 0 seconds.

[!cER]

Sleepy i agree with you, that was what i was trying to say when i said:

As both time and distance are continuous they should reach zero and the same time

Sorry that ive repeated and issue in an earlier thread , but thanks for all the intelligent responses

[EternalEntropy]

ok I'm sorry but you're an idiot. I made a nice long post explaining everything you asked about in detail. Yet you still go on about this infinite acceleration crap. Get it through your head, there is no infinite acceleration because all actions require time to do. You are thinking some bizaro stuff (wrong btw) that moving from 0 velocity to any speed requires an infinite acceleration.
The fact is that if you graphed the speed of the object it would look something like this.

Speed
|                                *
|                               *
|                             *
|                          *
|                     *
|               *           
|        *
|*
|______________________ Time

As with any graph, between two points there is an infinite number of smaller numbers. I think this is where you are confused. This doesnt change the fact that there is no infinite acceleration and that the difference between two speeds has a time associated with it, no matter how small (look at the graph).

[Monte Hazboun]

now I remember why I dropped outta university..

[Verthanthi]

Originally posted by EternalEntropy
stuff about things moving reletive to each other

Originally posted by Verthanthi
stuff about references frames

I say "tomato", you say "delicious red juicy thing". We're on the same page here, chummer.


Anyway, for the other guy, there have been a number of good explanations of why there is no infinite acceleration. If you're still not understanding the things we say, you probably won't until you've started calculus. If you are interested and it'll be a while before you can take calc, ask your parents/teachers about it, if they know I'm sure they'd be glad to give you a primer.

[poop juice]

"No matter how small the time interval, or how slowly an object moves during that interval, it is still in motion and its position is constantly changing, so it can't have a determined relative position at any time, whether during an interval, however small, or at an instant," - Peter Lynds