Unit 6 (Newton’s 3rd Law vs Equilibrium)

Question 1

When a boy pushes a wall; the wall pushes back on the boy! If the boy is wearing rubber shoes on a clean floor he can remain at rest, why? Is it because the action and reaction forces cancel each other out?

(yes or no)

Answer 1

No!

Question 2

Why can action–reaction forces NEVER cancel each other out?

Answer 2

Each force acts on a different subject/object. They can ONLY cancel out if the force is on the same subject.

Question 3

If the boy above pushes on the wall again… but this time is on a skateboard… why is the outcome different than when he was standing on the floor?

Answer 3

Because the forces are NOT balanced.

Question 4

If the boy above pushes on the wall again… but this time is on a skateboard… why is the outcome different than when he was standing on the floor?

Answer 4

Because the forces are NOT balanced.

Question 5

f 300 Newton girl stands on a scale what happens if she pulls down on a bar above the scale with a force of 75 N? (what would this look like on a free-body diagram?)

Answer 5

The scale reading will increase because the bar will push downward.