Passage IV

Physics students performed 3 studies to determine the forces that several doors exerted on their hinges. The doors had various weights, W, and widths, D. Each door had 2 hinges; the hinges could be moved to vary the distance, S, between them. None of the doors had a doorknob.

The 2 hinges on each door were equidistant from the center of mass of the door (see the diagram).

Each hinge was fitted with 2 force sensors. With the door attached to a door frame, one of the sensors detected the horizontal force exerted by the door on the hinge,, and the other sensor detected the vertical force exerted by the door on the hinge,. Once and were determined for each hinge, was averaged over the 2 hinges, yielding the average horizontal force per hinge,, and was averaged over the 2 hinges, yielding the average vertical force per hinge,· Fromand, the average net force per hinge,could be calculated.

In the 3 studies, all forces were recorded in pounds (lb) and all lengths were recorded in inches (in).

Study 1

For a door with W=61 lb and D=30 in, the students determinedandat various S. The results are shown in Figure 1.

Study 2

For 3 doors, each with D = 30 in but a different W, the students determinedat various S. The results are shown in Figure 2.

Study 3

For 3 doors, each with W = 61 lb but a different D, the students determinedat various S. The results are shown in Figure 3.