Section 5.1 Action-Reaction Pairs (Newton’s Third Law)
Subsubsection Key Ideas
Principle 5.1.2. Action-Reaction Pairs.
Forces come in pairs known as Action-Reaction Pairs. Since all forces arise from an interaction between two different systems, you can always find an Action-Reaction Pair to any force. Action-Reaction Pairs are always the same type of force, always involve the same two objects or systems acting on each other, and always have the same magnitude and point in opposite directions. The Action-Reaction Pair Principle is sometimes known as Newton’s Third Law of Motion.
Activity 5.1.1. Book at Rest.
(a)
When a book is sitting at rest on a flat table, there are two forces acting on it. Identify these two forces and explain why they are not Newton’s 3rd Law pairs.
(b)
Identify the Action-Reaction (Newton’s 3rd Law) pair for each force acting on the book from the previous question, which is sitting at rest on a flat table.
