An introduction to…Friction

In this experiment you will determine the frictional force between a wooden block and the bench top (or other suitable surface) as the load on the block is varied.

Refer to the diagram below.

Put a load of 200g on the wooden block.

Pull the loaded block horizontally at a slow, steady speed whilst noting the pulling force used. This will give a value for the dynamic friction force between the block and the surface.

Measure the mass of the wooden block.

Record the added mass, the total mass of block and added mass, pulling force measurements and the average pulling force for that load in a suitable table.

Repeat for added masses in the range 200g to 1000g.

Plot a graph of Average Pulling Force (y-axis) against Total Mass (x-axis).

Draw the best-fit line through your points.

It is suggested that the Pulling Force is directly proportional to the Total Mass. Comment on the extent to which your results support this suggestion.

The static friction force is the maximum force between two surfaces that are not moving. For a given load record the static friction force by noting the maximum force on the spring balance just before the block starts to move. The static force is greater than the dynamic force so it is harder to get something moving than to keep it moving. (What is the significance of this to ABS in vehicles?)

Take measurements to determine how the static to dynamic ratio depends upon the contact force (ie the total mass).

Apparatus:

Spring balance (10N)

1Kg ×100g mass set

Wood block with hook

Suitable surface