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Bernoulli Equation and Newton Law

  1. Sep 1, 2008 #1
    Hello friends,

    I have a problem in Bernoulli equation and Newton Law. I'm going to calculate how much power is needed to lift up an object with weight W.

    I'm planning to put the object in a 10 inches diameter. How can I calculate the power needed by the motor to lift up the object? Does the object has friction in it (the object will float)?

    The motor will be placed at the bottom of the tube and will give pressure to the object.

    I know that there is also an equation like: F= [tex]\frac{P}{A}[/tex]. but how to implement it? I have my assumption for this one that will happen with the object (Attached). Please correct me if I'm wrong.

    Any help means a lot.

    Thank you :)

    Attached Files:

  2. jcsd
  3. Sep 1, 2008 #2


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    Staff: Mentor

    That's a pretty difficult question, because it depends a lot on the geometry of the object - that's where coefficient of drag comes from.
  4. Sep 2, 2008 #3
    Hello Sir!

    Thank you for your reply.

    I have changed the design, right now I want to calculate drag force on this model (attached).
    There are two questions there. The first one could you give me a hint of how to solve the force of the slope area, and the second one is the drag force of the ball ( I don't use a aerodynamic law in here), you can assume the condition to help you give me a hint to solve this problem.

    What is the requirements to calculate them? Does Bernoulli Equation is still be used in here?

    Thank you.

    Attached Files:

  5. Sep 5, 2008 #4


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    Try to Google Rotameters (a device which used to measure flow rate). Their working principle is based on equilibrium between gravity forces and the forces from the flow, similar to your model.
    check this link for start:
    http://www.sensorsmag.com/sensors/Flow+Sensing/The-Basics-of-Rotameters/ArticleStandard/Article/detail/360731 [Broken]
    Last edited by a moderator: May 3, 2017
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