Question

3.3.2 test (cst): forces
question 13 of 20
which statement describes an action - reaction pair?
a. you push against a wall, and the wall applies a force to your hands.
b. you push a book off the edge of a shelf, and the book falls to the floor.
c. the sun pulls on the earth, and the earth pulls on the moon.
d. you throw a ball straight up, and earths gravity pulls it downward.

Explanation:

According to Newton's third law, for every action, there is an equal and opposite reaction. In option A, when you push against the wall (action), the wall pushes back on your hands (reaction). In option B, the book falling is due to gravity (not a direct reaction to the push). In option C, the Sun - Earth and Earth - Moon forces are not an action - reaction pair (they involve three objects). In option D, throwing the ball up and gravity pulling it down are not an action - reaction pair (gravity is a field force acting on the ball, not a reaction to the throw in the sense of Newton's third law for contact forces in this simple analysis).

Answer:

A. You push against a wall, and the wall applies a force to your hands.