S4.8.6 For the adult
Newton's third law
If every push has an equal push back, how can anything ever start to move?
What this chapter teaches
If A exerts a force on B, then B exerts a force of the same size and type on A, in the opposite direction. The two forces act on different objects, so they never cancel. A weight and the push of a table are not a pair.
Three questions to ask
There is no one right wording. Listen for the idea.
- When you walk, what is the pair of the ground pushing your foot forward?
- Why do the two forces of a pair not cancel each other?
- A book rests on a table. Which force is the partner of the push of the table on the book?
After the chapter, the learner can
- Identify force pairs in walking, swimming and rockets
- Explain why the two forces in a pair act on different objects
What they copy into their notebook
Third law: the two forces of a pair are equal, opposite, of the same type, and on different objects. They never cancel. A weight and the push of a table on a book are not a pair.