Subject: To accurately measre terminal velocity (ball bearings and viscous fluids)

I am trying to devise an experiment to find the effect of radius on the 
terminal velocity of ball bearings. I plan to do this by dropping the balls 
into a large cylinder containing a viscous fluid (golden syrup) I will allow 
sufficient distance for the balls to reach there TV and then I must measure the 
time taken to cover a certain distance. However I am having difficulties 
devising a way to accurately measure this time. One idea was to use light gate 
but I think the viscous and walls of the cylinder would diffract and refract 
the light beam. Do you have any solutions?

Re: To accurately measre terminal velocity (ball bearings and viscous fluids)