Third Law of Motion
The Sun and the Earth exert a force of gravity on each other. Draw a force diagram.
See Figure 3-8.
FES = gravitational force of the Earth on the Sun,
FSE = gravitational force of the Sun on the Earth.
Two spacecraft push off from each other. Draw a force diagram.
See Figure 3-9.
F12 = contact force of craft 1 on craft 2,
F21 = contact force of craft 2 on craft 1.
A basketball player jumps up. While he is in the air, he pushes the basketball horizontally. Draw all the forces while he is pushing the ball. Ignore the tiny gravitational force between the player and the ball.
See Figure 3-10.
Fpb = contact force of player on ball,
Fbp = contact force of ball on player,
FEp = gravitational force of Earth on player,
FpE = gravitational force of player on Earth,
FEb = gravitational force of Earth on ball,
FbE = gravitational force of ball on Earth.
Notice that the magnitude of the force of the player on the ball is the same as that of the ball on the player. But the player moves hardly at all, while the ball springs toward another player. Why is the basketball affected more than the player? (Hint: Look at equation 1.)