Day 56: Unbalanced Forces Lab


Physics 11 – Today the classes did the main modeling lab for unbalanced forces and Newton’s Second Law.  I’ve used the modified atwood lab in the past, but wasn’t satisfied with it due to friction and hand-waving with transferring mass from cart to hanging mass.  I also tried to setup an atwood apparatus as described by Josh Gates.  In this setup, you hang a mass from one side of the pulley, and on the other side you hang another mass via a force sensor.  If you time how long it takes for the force sensor to travel a certain distance, you can calculate its acceleration.  You get the Fnet directly from the force sensor. I also found this lab setup to be difficult, particularly because it really works best with a wireless force sensor.  In the end I opted to have the students get data directly from a force and motion simulation.

Prior to starting the lab, we qualitatively discussed unbalanced forces via Peer Instruction.  I did this instead of the suggested modeling lab with qualitatively measurement of pulling a person on a cart.  PI afforded some good discussion and I’m relatively confident that students understood the idea of unbalanced forces causing an acceleration.

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