Cracking the SAT Physics Subject Test

Once again, Situation 1 yields the fastest door-shutting results, followed by
Situation 2. (In Situation 3, the door is being pushed on, but it is not rotating.) In
this final example, the same angle and amount of force (100N) is used, but in
different locations.

SCENARIO 3

Same question: in which situation will I close the door faster?

Those of you who have tried this at home will immediately notice that the door in
Situation 2 closes much more easily. From these three scenarios, we can then make
the following conclusions about how to effectively spin or rotate an object:

• In Scenario 1, the amount of force used mattered, which is the
  magnitude of Force (F).


• In Scenario 2, the angle at which the door was pushed mattered,
  which is the angle (theta, θ).


• In Scenario 3, the location at which the force was applied
  mattered, which is the radius (r).

From that, we can write an equation for torque: