This document discusses Newton's Third Law of Motion and provides examples of action-reaction force pairs. It explains that for every action, there is an equal and opposite reaction. Examples given include a swimmer pushing off a wall and a person pushing a cart. The document then provides two problems checking understanding - the first about the relative forces on a firefly hitting a bus, and the second about the acceleration of a rifle compared to a bullet during firing. The answers explain that the forces are equal due to Newton's Third Law, but acceleration depends also on mass.

1. Chapter 4
NEWTON’S 3rd LAW OF MOTION
Action – Reaction Pairs Examples
Figures from OpenStax College, ancillaries to College Physics. OpenStax College. 21 June 2012.
http://cnx.org/content/col11406/latest/, licensed under a CC 4.0 International License, unless otherwise specified.

2. Newton’s 3rd Law
• For every action, there is an equal and opposite reaction.
“NewtonsLawOfUniversalGravitation.svg;” by Dna-Dennis derivative work: Onio72 (talk)) [CC BY 3.0 Unported]

3. Example 1 – swimmer pushing on a wall

4. Example 2 – Person pushing a cart

5. Check Your Understanding 1
While driving down the road, a firefly strikes
the windshield of a bus and makes a quite
obvious mess in front of the face of the driver.
The firefly hit the bus and the bus hits the
firefly.
Which of the two forces is greater: the force on
the firefly or the force on the bus?
http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm

6. Check Your Understanding 1 - Answer
The forces are equal! For every action, there is an equal
reaction. The fact that the firefly splatters only means that
with its smaller mass, it is less able to withstand the larger
acceleration resulting from the interaction.
http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm

7. Check Your Understanding 2
A rifle recoils when it is fired as a result of action-reaction
force pairs. A gunpowder explosion creates hot gases that
expand outward allowing the rifle to push forward on the
bullet. The bullet pushes backwards upon the rifle. The
acceleration of the recoiling rifle when compared with that
of the bullet is:
a. greater.
b. smaller.
c. the same.
http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm

8. Check Your Understanding 2 - Answer
Correct Answer: B
The force on the rifle equals the force on the bullet. Yet,
acceleration depends on both force and mass.
𝐹 = 𝑚 𝑎
The bullet has a greater acceleration due to the fact that it
has a smaller mass.
http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm