# Drag - Terminal Velocity of a solid sphere.

1. Apr 3, 2013

### MrWinesy

1. The problem statement, all variables and given/known data

A solid sphere - 20mm in diameter, σ (specific gravity) = 1.3

dropped in water μ=1*10^-3 and ρ=1000

determine the terminal velocity for the sphere.

(hint- guess the value for the drag coefficient then iterate)

2. Relevant equations

Fd=(1/2)*Cd*ρ*(U^2)*A

3. The attempt at a solution

tried guessing the drag coefficient but have no confidence in estimate or of the next step.

(also the relationship equation connecting viscosity, specific gravity and density would be much appreciated).

2. Apr 3, 2013

### rude man

What they have in mind I guess is this:
1. guess at the terminal velocity.
2. determine the Reynolds number for a sphere in water at that velocity.
3. Determine the drag coefficient based on the Reynolds number.
4. Compute the drag force based on c and v.
5. Compare with your guess of v.
6. Re-guess v etc.

There are several Websites that together can give you all the info you need:
1. kinematic viscosity of water
2. Reynolds number for a sphere at a given velocity
3. Drag coeff. as a function of the Reynolds number for a sphere.

Along the way you can pick up any theory and data you didn't know.