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Homework Help: Relation of Pressure and Weight of Air.

  1. Oct 3, 2006 #1
    The problem is in the context of your being a volleyball team manager and having to fill up the balls before a match...

    The question itself reads as follows:

    The game is only an hour away, so you start putting air in the first of your volleyballs. You open the ball's inlet valve and the ball fills with ordinary air at normal atmospheric density and temperature. The air in the volleyball now has a real (i.e., gravitational) weight of 0.1 newtons. When you place the ball on a scale, what measured weight does the scale report for the volleyball? Briefly explain the value reported by the scale.

    I cannot determine whether or not the ball would have any mass or not because in the opener of the problem set, my professor has stated that the skin of the ball has zero weight. Does this mean that the ball would weigh, in fact, zero? I find it hard to believe that air would weigh nothing, but I was discussing this with a friend and they tried to use the analogy of a vase-- technically there's still air in the vase since it's not a vacuum, but would that weight register on a scale?

    I tried thinking of air as a fluid and buoyant forces, but since the ball isn't floating, I'm not sure. I'm leaning toward zero weight just because the ball has same pressure as the weight around it, but I'm not sure this is the correct weight, or if it is the right answer, I can't articulate the logic behind it very well.

    Thanks for your help!

  2. jcsd
  3. Oct 3, 2006 #2


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    Think about what medium you're measuring it in. If you're measuring the weight of air in air, does it have any meaning?

    What about more dense air in less dense air (the case of the basketball)?
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