This is a simulation of a hinged rod in static equilibrium. The top picture shows the rod, supported by a hinge (in red) at the left end and a blue string at some point along the rod. The second picture of the rod shows the extended free-body diagram of the rod, showing all the forces acting on the rod and where they are applied. The force of gravity is shown in green, the two components of the force of tension are shown in blue, and the two components of the hinge force are shown in red.

You can use the sliders to control the position and angle of the string, as well as to set the weight of the rod.

There is also a checkbox which you can use to show an area representation of torque, the area having units of newton-meters. Taking the axis at the hinge, the torque from the force of gravity acting on the rod is shown in green, and represented by the green rectangle. That torque is directed clockwise. This is offset by the counterclockwise torque from the string, entirely associated with the vertical component of the force of tension.

The parallelogram representation comes from Brian Frank, who credited David Hestenes, but it also goes back much further than that, such as to William Clifford.

Simulation written by Andrew Duffy, and first posted on 8-21-2018.

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