2.3 Newton’s Third Law

For every action, there is an equal and opposite reaction.

${F_{A \text{ on } B} = -F_{B \text{ on } A}}$

These forces are equal in magnitude and opposite in direction, but they act on different objects.

Example: If a 5 kg block pushes on a 10 kg block with a force of 20 N, the 10 kg block pushes back on the 5 kg block with a force of 20 N in the opposite direction. Using Newton’s Second Law, their accelerations differ because of their different masses.