AP Physics C: Mechanics / Unit 2: Force and Translational Dynamics
2.3 Newton's Third Law
Notes
For every force A exerts on B, B exerts an equal and opposite force on A. The pair acts on different objects, so they don't cancel.
Practice
A truck hits a fly. The force on the fly compared with the force on the truck:
Third-law pair.
The Earth pulls you down with 600 N. You pull the Earth:
Equal and opposite.
Third-law pair forces don't cancel because they:
Each acts on a different body.
Ready for more? Take the Unit 2 test.