Class Exercise on force pairs

 

The free body diagram for our object looks like this:

The forces are:

A gravitational force (W) exerted on the block by the Earth

A normal force exerted on the block by the ramp.

A frictional force exerted on the block by the ramp.

 

The pair forces are:

A gravitational force exerted on the Earth by the block.

A normal force exerted on the ramp by the block

A frictional force exerted on the ramp by the block.

 

We should not draw these forces on the same diagram, since they are exerted on different objects. Instead we have:

 

Pair force exerted on the Earth:

Pair forces exerted on the ramp: