# Pendulum Damping Force

1. Dec 21, 2007

### geordieman101

[SOLVED] Pendulum Damping Force

1. The problem statement, all variables and given/known data
I am attempting to find the damping force of my pendulum using Stokes' Law. However, I am having trouble finding the velocity of the spherical object to get this damping force.
The radius of the sphere is 0.014m, the viscosity of air is 1.82 x10^5, the mass of the object is 0.035kg, the length of the pendulum is 2.3m, the time period is 3.274s
The pendulum was released from an amplitude of 100cm, at an angle of 23.5 degrees or 0.41 radians

2. Relevant equations
F(damping)=-6πrηv
v=rw
2π/w=T=2πr/v

3. The attempt at a solution
Using 2π/w i managed to get the angular velocity of 1.92rad/s and therefore my calculation for the velocity is 0.02688m/s, and thus my calculation for the damping force as 1291N, but this seems to be too large compared to the weight in the opposite direction of the force being shown via mgsinθ or in this case mgθ

2. Dec 21, 2007

### Dick

1291N is ridiculous. Isn't the exponent on the viscosity of air number -5, not +5.?

3. Dec 21, 2007

### geordieman101

yes it is, my bad, but this would give the damping force as 1.29x10^-7N, surely this would be too small compared to 0.14N is what I am getting for the force of mgθ, the force due to gravity also seems incorrect to me as well

4. Dec 21, 2007

### Dick

I get the same thing for the damping force. Air is not very viscous. I don't see anything wrong with your g force either.