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Need help explaining this video

  1. May 27, 2006 #1

    near the end of the video clip, the pilot does a "roll" and at the same time he is pouring water into a cup even though when he is now in an upside down position the water does not spill out of the cup, how is that possible?
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. May 27, 2006 #2

    Andrew Mason

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    The fact that the tea in the cup does not spill is easy to explain but just why the tea continues to pour is a little trickier.

    Analyse the forces on the tea in the cup as the plane is doing a roll. What are the forces acting on the tea? (think of the roll as circular motion about some point).

    Last edited by a moderator: Sep 25, 2014
  4. May 27, 2006 #3
    The spoilers are in the same color as the background.

    Imagin that you are holding a piece of string with a cork attached to the other end. If you start to spin the string above your head you will that you must hold against to stop the cork from flying away. If you release the string the cork will indeed fly away in the direction of the tangent:


    You need to use a force to stop the cork from flying away. This force is used to change the path of the cork so it moves in a cirular movement. This force is called centripetal force and is directed to the center.

    The phenomena can also be observed in roller-costers. What makes a roller-coster continue without "falling off" in a loop?

    The short answer is its speed.

    The larger the speed the larger is the force that is directed to the center. If that force passes a certain magnitude the item will stay in its orbit.

    You can verify this by yourself in a simple experiment. If you take a glass of water and turn it really quickly around, not fluid will be lost. Do it slower and all of the water will pour out.
  5. May 27, 2006 #4
    is there a specific name for this effect?
  6. May 27, 2006 #5


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    This is a simple application of circular motion, as the other posters have said you need only consider the forces acting to explain the effect.

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