**Physlet Physics: Newton's Third Law and Contact Forces**

*Interactive Animation*

This animation gives students the challenge to match the motion of a particular physical situation involving a two-body system. Given a net force of 12N, students must determine the correct ratio of contact forces between the larger and smaller block to make the animation run as it should. (Hint: Even if students have to do some trial and error, they should figure out that the force on the smaller green block must be equal, but opposite to, the force on the larger red block. This bears out Newton's Third Law, and gives kids a chance to model the situation in a unique way.)

**PhET Simulation: Gravity Force Lab**

*Mobile-Friendly Interactive Simulation*

In introducing force pairs, it can be useful to examine Newton's Third Law in the context of gravitational attraction. This resource helps students visualize the gravitational force that two objects exert on each other. No matter how you change the mass of either object, they exert the same amount of gravitational force on each other. They are force pairs that obey Newton's Third Law.

*Teachers: For a great video explanation to supplement this sim, see Veritasium's "Best Film Ever on Newton's Third Law" in Expert Views tab above.*