Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

A barge

A barge is being pulled along a canal by teams of horses on the shores. Analyze all the forces in which the barge participates.

force acting on bargeforce related to it by Newton's third law
ropes' forward normal forces on bargebarge's backward normal force on ropes
water's backward fluid friction force on bargebarge's forward fluid friction force on water
planet earth's downward gravitational force on bargebarge's upward gravitational force on earth
water's upward "floating" force on bargebarge's downward "floating" force on water

Here I've used the word "floating" force as an example of a sensible invented term for a type of force not classified on the tree in the previous section. A more formal technical term would be "hydrostatic force." Note how the pairs of forces are all structured as "A's force on B, B's force on A": ropes on barge and barge on ropes; water on barge and barge on water. Because all the forces in the left column are forces acting on the barge, all the forces in the right column are forces being exerted by the barge, which is why each entry in the column begins with "barge."

Last Update: 2009-06-21