Viscosity,Fluid flow and terimal velocity

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SUMMARY

The discussion centers on the conditions under which the buoyant force (Fb) equals the drag force (FD) for a sphere moving through a fluid. The buoyant force is defined as Fb = ρVg, where ρ is the fluid density, V is the volume of the sphere, and g is the acceleration due to gravity (9.80 m/s²). The drag force is given by FD = 6πηrv, where η is the fluid's viscosity, r is the sphere's radius, and v is its velocity. The relationship Fb + FD = Fg indicates that the forces acting on the sphere must balance for it to reach terminal velocity.

PREREQUISITES
  • Understanding of buoyancy and Archimedes' principle
  • Familiarity with fluid dynamics concepts, specifically drag force
  • Knowledge of basic physics equations involving force, mass, and acceleration
  • Basic understanding of viscosity and its role in fluid flow
NEXT STEPS
  • Study the principles of buoyancy and how they apply to objects submerged in fluids
  • Learn about the derivation and application of Stokes' Law for drag force
  • Explore the concept of terminal velocity in different fluid mediums
  • Investigate the effects of varying viscosity on the motion of spheres in fluids
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in fluid mechanics, particularly those studying the dynamics of objects in fluids and the forces acting on them.

ChunkymonkeyI
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Homework Statement


When does Fb(Buoyancy force) equal the drag force(FD)?
and Fb+FD=Fg

Homework Equations


Fb=density of water times volume of water times 9.80 m/s^2
FD=6pi times viscosity times radius times v
Fg=mg

The Attempt at a Solution


All ik is the solid has 2 be in the air going to the water but idk how 2 really prove that please help me
 
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This problem is really confusing. Do we have a ball falling in water? Not sure what is going on here.
 
It is a sphere of radius r moving with speed v in a fluid of viscosity η. The drag force is FD=6πηrv.
The buoyant force is FB=ρVg, where ρ is the density of the liquid and V is the volume of the sphere.

ehild

PS: ChunkymonkeyI, what did you mean: "All ik is the solid has 2 be in the air going to the water but idk how 2 really prove that please help me" We use English here.
 
Last edited:

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