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sunnyguha
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If a sphere is moving through air.
Will it have more drag if it is spinning while moving or just moving ?
Will it have more drag if it is spinning while moving or just moving ?
sunnyguha said:If a sphere is moving through air.
Will it have more drag if it is spinning while moving or just moving ?
Lsos said:The side that is spinning into the direction of the ball's motion will have more friction than the side that's spinning away from from this direction (since it's moving faster with respect to the air). Since drag rises with speed squared, the side spinning into the direction of motion will have gained more drag than the other side will have lost, and therefore the total drag will be greater.
MikeyW said:If you're integrating drag (speed^2) over a surface, you've just assumed that the size of the two surfaces are equal. What if the higher drag surface is smaller?
boneh3ad said:Yes. It would change the location of the forward stagnation point as well as the separation lines as opposed to a sphere that isn't spinning. It would also change the character of the von Kármán vortex shedding.
sunnyguha said:If a sphere is moving through air.
Will it have more drag if it is spinning while moving or just moving ?
Andy Resnick said:The drag is different, I'm not sure if it's more or less. The Magnus effect is the reason curveballs curve:
http://en.wikipedia.org/wiki/Magnus_effect
And this effect was also put to use (the Flettner rotor)
http://en.wikipedia.org/wiki/Rotor_ship
MikeyW said:I have a feeling it may be the same. The rotation breaks the vertical symmetry because the stagnation points move, but I don't believe it breaks the upstream/downstream symmetry (apart from the direction of the flow, which shouldn't affect the following argument).
MikeyW said:To find drag you're integrating pressure times the normal vector around the surface of the sphere, and taking the horizontal component. Pressure is not affected by direction of flow, only speed (therefore it is upstream/downstream symmetric), so an integration of the horizontal component of the normal times pressure will be zero due to cancellation of the upstream/downstream hemispheres.
The present study numerically investigates two-dimensional laminar flow past a circular cylinder rotating with a constant angular velocity, for the purpose of controlling vortex shedding and understanding the underlying flow mechanism... α is the circumferential speed at the cylinder surface normalized by the free-stream velocity. Results show that the rotation of a cylinder can suppress vortex shedding effectively... With increasing α, the mean lift increases linearly and the mean drag decreases, which differ significantly from those predicted by the potential flow theory.
Drag is a force that opposes the motion of an object as it moves through a fluid (such as air or water). It is caused by the friction and pressure differences between the fluid and the surface of the object.
Drag slows down the motion of an object by exerting a force in the opposite direction of its motion. This force increases as the speed of the object increases and can eventually balance out the force propelling the object forward, causing it to reach a constant speed.
The amount of drag on an object is affected by its size, shape, speed, and the properties of the fluid it is moving through. Objects with larger surface areas, streamlined shapes, and higher speeds experience greater drag.
Drag can be reduced by changing the shape or surface of an object to make it more streamlined, or by reducing its speed. In some cases, adding a fluid layer (such as a lubricant) can also help to reduce drag.
Drag is an important concept in many fields of science, including aerodynamics, hydrodynamics, and fluid mechanics. It is also relevant in areas such as sports (e.g. reducing drag in swimming or cycling), transportation (e.g. designing more efficient vehicles), and even biology (e.g. understanding the movement of organisms through fluids).