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Bernoulli's Equation with a ping pong ball

  1. Aug 14, 2013 #1
    1. The problem statement, all variables and given/known data

    There is a ping pong ball being lifted and suspended in the air by a hair dryer. A.)What is the upward vertical force needed to suspend the ping pong ball? A ping pong ball has a Mass of about 2 grams. B.)If the pressure underneath and inside the ping pong ball is 1 atm what is the pressure above the ping pong ball in newtons per square meter and C.)what is the average speed of the air in m/sec.

    2. Relevant equations

    Bernoulli: P+(1/2)ρV^2+mgh= P+(1/2)ρV^2+mgh
    P=F/A

    3. The attempt at a solution
    For A.) I started with P=F/A and i assumed that the Pressure would be that of 1 Atm and the area of a ping pong ball would be around .005 m^2 based on experience. So the force I got was .005 newtons. I feel that I am extremely off.
    For B and C) I used the bernoulli equation but mixed and matched symbols and somehow got huge numbers. A walk through of how to approach this problem would be greatly appreciated.
     
  2. jcsd
  3. Aug 14, 2013 #2

    rcgldr

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    Homework Helper

    The size of an official ping pong ball is 40 mm, and the mass is 2.7 grams. If the ball is hovering, then the drag force equals the weight of the ball, about 26.5 N, but part of the drag is due to increased pressure below the ball and decreased pressure above the ball.

    It ends up complicated, since the coefficient of drag for a sphere depends on smoothness, wind speed, and the size of the ball, and there are issues like turbulence. Link to Nasa article:

    http://www.grc.nasa.gov/WWW/K-12/airplane/dragsphere.html
     
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