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Weightlessness in a common swing

  1. Feb 12, 2012 #1

    Our sensation of weight is given by gravity together with normal forces. It is said that in a swing you'll feel weightless at the top of the ride (180 degrees), because there is no seat that gives you normal force. But from my experience there is something strange even before 180 degrees, when swing stops and goes other way around, just like a free fall. It might be just because after 90 degrees there is no force projection on the seat as well? And this "180 degree fact" is slightly wrong?

  2. jcsd
  3. Feb 12, 2012 #2
    Interesting. I must admit I have been to numerous parks with my kids....used the swings and thought about what's going on as well as watch them playing on them.
  4. Feb 12, 2012 #3


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    When you swing, you will feel a centripetal force pressing you against the seat (more correctly, pressing the seat against you) but that has nothing to do with gravity- you would feel it even if you were "swinging" in a weightless environment. Of course, in that case your swing would just keep going in a circle.
  5. Feb 12, 2012 #4
    You feel a normal force, because of the centripetal acceleration needed to make you follow a circular arc, and because of the radial component of gravity.

    When the swing is a its highest point, there is no centripetal acceleration and there's only the force of gravity.

    If the swing makes an angle A with the vertical, the force of gravity mg on you will have a component mg sin (A) wich will accelerate the swing tangentially, but will not be felt by someone on the swing. There is also a component mg cos(A), in a radial direction to the outside wich is compensated by a normal force in the opposite direction.

    The normal force that you feel on the swing (mg cos(A)) becomes 0 when the swing is at 90 degrees. If this is the highest point, you'll be weightless at this point.

    On a swing with ropes or chains, you can't go higher than that, unless you go so fast, that the centripetal acceleration at the top of the swing is equal to the acceleration of gravity, and you are then weightless at 180 degrees. This is hardly swinging, because you'd turn circles.

    If you make swing with bars, it's possible to swing higher than 90 degrees.(if you can hold on). You would actually become weightless somewhere between 90 degrees and the highest point. (at 90 degrees, there's an inward normal force needed, at the highest point, there's an outward force needed, so you won't fall off head first)
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