# The Ball Bearing Problem

#### Endorser

Hello All,

I have been giving a practical assignment to calculate how terminal velocity changes as the diamter of ball bears increase. I have chosed to use stokes law
http://en.wikipedia.org/wiki/Stokes'_law to assist me with the prac.

I required different sized ball bearing but must be of the same weight, using a lathe is way to extreme for this, how else can i get hold of ball bearings off different diamater and the same mass.

They must be of the same materical preferable steel.

thanks

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#### ideasrule

Homework Helper
If you want different diameters with the same mass, the density of the ball has to change, meaning you need to use a different material for each ball. That's not practical, so why not use the same material and vary both mass and radius? Terminal velocity will still change with changing radius, and it's not hard to arrive at a theoretical prediction once you know the material's density.

#### Endorser

so why not use the same material and vary both mass and radius? QUOTE]

The assesment task asks me to measure different "sphere diameters" not different mass or material or density

#### lewando

Homework Helper
Gold Member
If you want to control the mass and vary the diameter, consider using StyrofoamTM spheres of varying diameter. You can adjust the mass by installing screws, nails, coins, etc.

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