
Aim: to estimate the Coefficients of Friction for two
solid surfaces 
If necessary, see the coefficients of friction
and friction, example. 

Dynamic Friction 
Method 
It is suggested that the force of friction be
measured using apparatus as shown below. 

We will be finding the coefficient of friction
between the wood or metal (or whatever) and the surface
of the bench (or whatever covers the bench). 
For a range of loads, find the force, mg which is
needed to keep the object moving at approximately
constant speed once you have given it a small push to
start it moving. 
Why do you need to give it a push? 
Find the coefficient of dynamic friction from a suitable graph. 

Static Friction 
Put the object on the surface and slowly increase
the angle of the slope. 
Find the maximum angle at which the object remains
stationary. 

Just before the object starts to slip down the
slope, the forces acting on it are in equilibrium. 
Therefore, the magnitude of F_{f} must be equal to a
component of mg and the magnitude of R must be equal to
another component of mg. 
Using these ideas you should be able to show that
the coefficient of static friction
μ_{s} is given by 

where θ is the
maximum angle at which the body remained stationary. 