# Instantanious speed

Discussion in 'Physics & Math' started by Jimbothegreat, Jan 17, 2003.

1. ### JimbothegreatRegistered Member

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Is it possible to measure the instantanious speed? Like, when a car is moving along, to figure out its speed, you need to know how far it moved in a set time. How can you find how fast it is traveling at an INSTANT in time. I am stuck because it must have a speed but isn't speed defined as the ditance traveled in a certain amount of time? What if time = 0? Any thoughts?

3. ### spookzBannedBanned

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nope
just a stoned giggle

5. ### IggDawgRegistered Senior Member

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calculus. or limits if you're the masochistic type. but those are just extremely good approximations. there's really no way to get perfect instantaneous speed, since there is no such thing as an infinitely small slice of time. I think the Planck time is about as close to the quantum unit of time as we have, and it's non-zero of course. so barring any further drolling on I'll just say "no"

-IggDawg

7. ### notme2000The Art Of FactRegistered Senior Member

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I actually read a new scientific theory in Popular Science a couple months ago. Perhaps time does equal 0. It doesn't exist. There is an infinite amount of still frames and our consciousness is passing thriough each of them. But the thing is, it doesn't even have to happen in order. For exampine, if in one frame you are falling, you'd think in the next frame you'd land, but perhaps in the next frame you're waking up, but IN THAT FRAME you have the memory of going to sleep the night before, and no memory of falling. So time would be 100% illusion...

8. ### chrootCrackpot killerRegistered Senior Member

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It is not possible to build an instrument which measures instantaneous speed, but it possible to work with the concept theoretically.

- Warren

9. ### chrootCrackpot killerRegistered Senior Member

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This is an example of why one should not read Popular Science to learn about metaphysics....

- Warren

10. ### notme2000The Art Of FactRegistered Senior Member

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The whole theory was very toungue in cheek, they didn't pass it off as credible or anything.

11. ### On Radioactive Waveslost in the continuumRegistered Senior Member

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The heisenberg uncertainty priciple would say- no, you cannot know exactly the position and velocity.

12. ### blobranaRegistered Senior Member

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The uncertainty principle is a perhaps a convenient way to describe the way that , as in a reel of film, an event (single frame) give you no exact information about the previous events (frames).
The new thinking is that time it self is a quanta ( 10 power -42 seconds) and that it is actually a vibrating string/membrane (?) and forms the space/time from which particles ( different vibrations of this) arise.

13. ### hlreedRegistered Senior Member

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What do you think a speedometer on your car measures?

14. ### notme2000The Art Of FactRegistered Senior Member

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Movement. Without time, there is no movement, thus no speed. Let's say time froze as a car was going 200 miles an hour, when time continued would the car STILL be going 200 miles or would it stay stationary?

15. ### chrootCrackpot killerRegistered Senior Member

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It measures the number of times the wheel turns in a small interval of time. It measures an approximation to the instantaneous speed.

- Warren

16. ### hlreedRegistered Senior Member

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If you are at x, then your velocity is dx/dt no matter how you are moving.
That is what a speedometer does.

17. ### chrootCrackpot killerRegistered Senior Member

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No real speedometer does this. Only an ideal one.

- Warren

18. ### hlreedRegistered Senior Member

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Warren,
You must not like machines. You are one you know.

19. ### chrootCrackpot killerRegistered Senior Member

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Uh what? Crack open an engineering book, skippy.

- Warren

20. ### On Radioactive Waveslost in the continuumRegistered Senior Member

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Oh yeah? What if you were moving in place, aka rotation ? Then x would not change, yet you would still have a velocity, measured in cycles per time unit.

Also, the spedometer only measures the wheels spinning. It wouldnt work in the case of skidding with your tires locked up even though the car is still moving.

21. ### RamblerSenior MemberRegistered Senior Member

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I am assuming in this example you are not able to measure anything using a time interval?? since velocity is the rate of change of position (dx/dt) it would seem that you can not measure the speed...

what if you were able to measure the kinetic energy of the vehicle at time t = 0 (by destroying it??) if you could measure that then you would have the speed it was travelling at the time you measured it's kinetic energy??

22. ### WhiteKnightRegistered Member

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Measure the air resistance. :bugeye:

23. ### IggDawgRegistered Senior Member

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Upon reading the replies since my post I'm going to have to go with the unceartainty thing. I hadn't thought of that.

But as far as getting the best working approximation which is all that matters anyways, I think calc would be your best bet. get an accelerometer and tally the frame by frame readings. then integrate. That's really the best way to go about it. if you tried to get a REAL instantaneous speed reading, you'd end up with some unsolvable equation due to quantum mechanics.

-IggDawg