- #1
daniscp
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Is there any experiments I could do to prove that the Drag Coefficient of a Sphere is more or less 0.5 depending on the roughness of the sphere?
Experimental work to prove that the Drag Coefficient of a sphere is 0.5
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Discussion Overview
The discussion revolves around experimental methods to determine the drag coefficient of a sphere, specifically focusing on whether it can be shown to be approximately 0.5, with considerations for the sphere's surface roughness. The scope includes experimental design and measurement techniques.
Discussion Character
- Exploratory, Experimental/applied, Technical explanation
Main Points Raised
- One participant inquires about possible experiments to demonstrate that the drag coefficient of a sphere is around 0.5, depending on its roughness.
- Another participant suggests using a wind tunnel or levitating the sphere in a vertical tube to measure its terminal velocity, or alternatively, dropping the sphere and timing its fall to compare calculated fall times with and without drag.
- A participant expresses frustration about not being able to devise an experiment to measure drag force, despite having access to a wind tunnel.
- One suggestion includes using strain gauges to measure drag force.
- Another participant proposes measuring flow velocity behind the sphere using a pitot tube to calculate momentum change, which could provide a drag coefficient value near 0.5, with some uncertainty.
Areas of Agreement / Disagreement
Participants do not reach a consensus on a specific experimental method, and multiple approaches are discussed without agreement on which is best or most feasible.
Contextual Notes
There are limitations regarding the assumptions made about the conditions under which the drag coefficient is measured, such as the effects of surface roughness and the accuracy of the measurement techniques proposed.
Who May Find This Useful
Researchers and students interested in fluid dynamics, experimental physics, and those looking to explore the relationship between surface characteristics and drag forces on objects in fluid flow.
- #2
Mech_Engineer
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The obvious question- do you have access to a wind tunnel?
Other than that, it might be possible to levitate the sphere in a vertical tube with air blowing through at its terminal velocity, or perhaps drop the sphere a long distance and measure its fall time very precisely, and compare that time to a calculated fall times with and without drag?
Other than that, it might be possible to levitate the sphere in a vertical tube with air blowing through at its terminal velocity, or perhaps drop the sphere a long distance and measure its fall time very precisely, and compare that time to a calculated fall times with and without drag?
- #3
Mech_Engineer
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I recognize your name now... Isn't this basically a repost of your previous thread?
- #4
daniscp
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Mech_Engineer said:
Yeah I have access to a wind tunnel...
It's not a repost since I've decided now to focus on proving that the drag coefficient of a sphere is 0.5. The only thing I need to think of is an experiment to measure the drag force...but can't come up with one
- #5
brewnog
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How about some strain gauges?
- #6
jaap de vries
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You can measure the flow velocity behind the ball using a pitot at several locations that you can calculate the momentum change which is equal to the drag force so you divide that by D*rho*V^2*0.5 and you will probably get a value near 0.5 (plus or minus 0.5).
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