Day 66: Newton’s 3rd Law

Physics 11 – We started off with a short look back at the conceptual work we did with gravity.  In particular, we reviewed how the gravitiational force between two objects is the same for both objects.  This was demonstrated using some scaffolded models and a tug-a-war with force gauges.  This work set a good foundation for Newton’s 3rd Law.

Having covered spring forces and gravity, the above video gave the students a convincing argument that interaction pairs have equal and opposite forces, regardless of the masses involved.  Once again, many thanks to Frank Noschese for his invaluable sharing of ideas, experience and resources.

Next we came back to how we do Force Diagrams (Free Body Diagrams):

pair

The students were now given a second reason on why they’re asked to label forces with the details of “_____ on _____”.  The first reason given was that if they student couldn’t figure out the agent that was causing the force, there is a good chance that they are imagining a force that doesn’t exist.  Today, the second reason given is that this description clearly outlines the interaction pair.

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