Decreasing diameter of a spehere and drag

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SUMMARY

The discussion centers on the effects of decreasing the diameter of a sphere on its falling rate through a liquid, specifically examining Stoke's Law and buoyancy principles. According to Stoke's Law, the drag force decreases with a smaller radius, suggesting a faster fall. However, the derived velocity equation indicates that a smaller radius results in reduced velocity due to the interplay of buoyancy, drag force, and weight. This contradiction highlights the complexity of fluid dynamics and the need for careful consideration of all forces acting on the sphere.

PREREQUISITES
  • Understanding of Stoke's Law and its application in fluid dynamics
  • Familiarity with buoyancy principles and Archimedes' principle
  • Basic knowledge of forces including drag, buoyancy, and weight
  • Ability to manipulate and solve equations involving fluid dynamics
NEXT STEPS
  • Research the implications of Stoke's Law on different shapes and sizes of objects in fluids
  • Explore the relationship between drag force and velocity in various fluids
  • Study the effects of fluid density on the buoyancy of submerged objects
  • Investigate experimental methods to measure the descent of objects in viscous fluids
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Physics students, engineers, and anyone interested in fluid dynamics and the behavior of objects in various liquids.

wkfrst
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Hey all,
I have been mulling this around in my head for awhile and cannot make sense logically.
In thinking about a sphere falling through some random liquid, how does decreasing the diameter of the sphere affect the rate at which it falls?

I am thinking of two formulas and the seem to contradict each other in terms of their results.
First would be Stoke's law dealing with drag force:
F(d)= 3(pi)μVd
Here if I reduce the radius, the force of drag decreases which makes me think the sphere would fall faster because it has less resisting its fall.

The next would be a derived equation using the force of buoyancy, drag force, and weight. This assuming these are the only three forces on a falling sphere. It is solved for velocity.
V= [2r^2(ρ(sphere)-ρ(fluid))g]/(9μ)
Here it appears that if the radius is reduced, the velocity is also reduced and it therefore falls slower.
My "logic" tells me a smaller sphere would fall faster, but it has failed me many times in physics.
Thanks for the help.
 
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