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How much centrifugal force?

  1. Apr 27, 2009 #1
    i'm looking for some kind of formula for how much centrifugal force an object in motion has. for example i have a metal ring spinning x fast how much force is there. it a brake was applied to it so to speak how much force would be exerted on the break. i have a idea that is going to revolutionize space travel and make it possible for anyone.
     
  2. jcsd
  3. Apr 27, 2009 #2
    F = dp/dt is all you need to know, where F = force, and dp/dt is change in momentum with respect to time.

    How can you make space travel available to everyone when you don't even understand newtons second law of motion?
     
  4. Apr 27, 2009 #3
    just because i don't understand the math doesn't mean i don't understand how it works i just don't know how to get figures so to speak. i don't understand the dp/dt thing can u explain that. i think i can convert centrifugal force to linear with my idea but i need to get the ring spinning so fast that my "brake" don't actually stop the centrifugal force.
     
  5. Apr 27, 2009 #4

    berkeman

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    Staff: Mentor

    dp/dt is the calculus representation for the change in momentun per unit time. p = mv is the linear momentum, with m = mass and v = velocity.

    It would be good for you to find a basic physics book at your local library or bookstore, and spend some time learning the basics of mechanics. You don't necessarily need calculus to understand the most basic formulas and concepts. But at some point, it would be good for you to pick up differential and integral calculus, to help your understanding of basic physics better.

    Will you be able to take physics and calculus soon? What year are you in high school?
     
  6. Apr 27, 2009 #5
    lol i'm out of high school. i didn't take any physics classes. i've started college for biochemistry but i had some financial problems so i'm waiting until i get this state job i applied for to go back. What does the d stand for?
     
  7. Apr 27, 2009 #6

    berkeman

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    The d stands for a differential, which is part of differential calculus. Here's a reasonable intro to differential calculus that starts with the basics:

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

    A differential is a "change", so dp represents a change in momentum. But the differential is special, because when you write dp/dt, that means the change in momentum during a change in time, but you shrink the time interval infinitessimally small. That gives you the most accuracy, when you express dp/dt as a continuous function, just like the velocity as a function of time is continuous.

    There are pretty good tutorials for mechanics, physics, calculus, etc. on the Internet. There's a good MIT video series as well... I'll see if I can find the link. It's listed over in the PF Learning Materials forum, I think.....
     
  8. Apr 27, 2009 #7

    berkeman

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  9. Apr 27, 2009 #8
    k i don't know if this formula is going to work for me then. I've been told that with physics its impossible to do what i'm trying to do but i don't see why its not possible and my ideas have been deleted off of here so i try not to talk about them on here. but i've seen videos on youtube of people successfully changing centrifugal force to linear ok i got a simpler version of my idea. if you have a metal ring lets say spinning at 1/4 of light speed and you have a "brake" so to say to act against it but not enough to stop it just to apply a force in a certain direction and on the opposite side of the ring you have something equally as powerful on the otherside acting to keep it going in the same dirrection as its already spinning. but if you put this picture in your head the left one acting against it will create an upwards force and the right one trying to keep it spinning acting against the other brake will have an upwards force as well but i'm imagining no where as near. I've talked to john Hutchinson he thinks my idea will work but hes the only other person that does.
     
  10. Apr 27, 2009 #9
    I do greatly appreciate your help by the way its very helpful
     
  11. Apr 27, 2009 #10

    berkeman

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    I remember a long time ago, I was trying to come up with a mechanism that would do something similar -- convert rotary motion and energy into linear motion. The problem is that for an isolated system (nothing goes in or out), momentum is conserved and cannot change. So, whatever your linear momentum is to start (p=mv), that's what you are stuck with, no matter what you do in that closed system. The only reason rockets can fly through space, is that the fuel that they burn ejects mass out the nozzle. This shoots some mass one way, and the mass of the rocket goes the other way.

    So any trick that you could think of to convert isolated rotational motion into isolated linear motion, would violate the conservation of linear momentum principle. And that is extremely unlikely/impossible.

    That's why it is good to learn as much real math and physics as you can, so that you don't waste any brain cycles on something that is basically impossible. That frees up brain cycles to work on hard science problems that *may* be possible, and believe me, there is plenty of room for invention and innovation in the realm of real science.
     
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