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How Centrifugal Force Works

  1. Jun 14, 2003 #1


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    Ok, for some reason, I cannot understand exactly how centrifugal force works or the concept behind it. For example, when an Army helicopter is flying through the air and turns, why don't the soldiers slide towards the door or even fall out? Because I know that military choppers do not contain seat belts except in the cockpit. Can someone please explain to me how this happens or why it happens?

    I know its a newb question, but I'm just starting to enjoy and learn about physics and mathematics. Also, this isn't homework so I'm assuming this is the right forum. So go easy on me .
  2. jcsd
  3. Jun 14, 2003 #2
    acceleration is any change in velocity. Velocity has direction as well as magnitude. When the magnitude changes, such as linear acceleration, any massive object will feel a force F = ma. When velocity direction changes, you also have an acceleration. In a circle, this acceleration is a=v2/R, where v is the tangential velocity (if mass were to continue in straight line) and R is distance from center of circle. So then, the force of any circular motion (toward the outside of the circle) will be F = mv2/R.
    The reason the airmen dont fall out of the chopper is that the friction forces between the men and the seat are greater than the acceleration forces acting to push them around. Also, choppers tend to bank when they turn, directing the total acceleration (componant vector with acceleration of gravity) down into the seat.
  4. Jun 14, 2003 #3


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    Staff: Mentor

    Take a yoyo, let it settle all the way at the bottom, then whirl it around in a circle as if the yoyo were orbiting your finger. Feel the force? How about in your car when its turning?

    ANY curved motion has an associated acceleration causing a centrifugal force.

    Your helicopter example is a special case. A plane or helicoptor banks at a very specific angle for a specific rate of turn because a plane or helicoptor doesn't fly sideways very well. As a result, the component of the force of gravity pulling the soldiers toward the lower door is exactly balanced by the component of the centrifugal force pushing them towards the other door. Have you ever ridden in a plane? Generally, you won't even know you are turning unless you look out the window.
  5. Jun 14, 2003 #4
    Umm, i personally find your example misleading.
    As far as i remember centrifugal force is only felt by objects inside the rotating frame of refference, and since in your example the person't frame of refference is not the same of the yoyo's, then person is not feeling any centrifugal force (what he is feeling is the centripetal force).
    Am i right ?
  6. Jun 15, 2003 #5


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    Staff: Mentor

    Dunno. My physics teacher always used to say that a centrifugal force doesn't exist - its actually a centripetal acceleration. I said ok, but I'm not really sure. Whatever you call it, my point was that to keep the yoyo going around in the circle requires a constant force from your finger.
  7. Jun 16, 2003 #6
    Let me explain a little bit.
    If you are in an inertial frame of refference (a non-accelerating frame of refference), and an object is moving in circular motion (say, the yoyo is moving round your finger), you can observe an acceleration causing the circular motion and pointing towards the center of the circle (your finger in our example) when the speed (and not velocity) of the moving object is constant, this is a centripetal acceleration (caused by a centripetal force), which is what you feel as tension in the string of the yoyo, or what you feel by your finger.
    Now, if we supposed that a little ant was on the yoyo, the ant in not in an inertial frame of refference (since its frame of refference is accelerating towards the center of the circle), the ant feels that it will fly off the yoyo (and away from the center) this is called a centrifugal acceleration, caused by a centrilfugal force (remember how you feel when you are in a speedy car on a corner).
    If we try to understand why the ant feels so from an inertial frame of refference, we will see that the velocity of the ant at any moment is a tangent line to the circular motion, the ants body tends to stay in in that velocity, but the yoyo is moving (its velocity is going away from the velocity that the ant's body tend to conserve), so the ant feels like it is going outside of the circle at any moment (try to see what happens if the ant leaves the yoyo at any moment, and you look at both of them (the ant and yoyo) after some seconds, you will see that the ant's displacement will be to the outside of the circle).
    Maybe if you try to draw a little illustration you will know what i mean.
  8. Jun 17, 2003 #7
    Inertia can be felt whenever acceleration is present on a moving body. Acceleration:(1)Change in speed. (2)Change in direction. (3)Change in both speed snd direction.
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