68 (This is for yesterday, only I fell asleep right after dinner and didn’t post it then) This is one of my favorite AP labs. Static equilibrium! I set up six stations each with a meterstick that has some masses resting on it or hanging off it. Two trusses, two supported by two tension forces, and two with one end supported on a rod clamp and the other pulled in the other direction by a tension force. Two have unknown masses, two have unknown tension forces, and two have unknown meter stick masses. All the tension forces have a spring scale attached, but the “unknown” tension forces have paper wrapped around them so they can’t be read. Students have to take whatever measurements they can (I give them protractors, rulers, one more meter stick, and a plumb bob) on two of the stations and determine the unknown value. They must also provide me with equations for net force and net torque.
Net Torque Equals Zero