# Newton's third law of motion

##### Intros

###### Lessons

##### Examples

###### Lessons

**Understanding Newton's third law and free body diagrams**A rock sits on a table. Draw complete free body diagrams for the rock and the table and highlight the action-reaction pair that includes the rock pushing down on the table.

**Calculations with Newton's second and third laws**- An 85.0 kg fireman slides down a pole with an acceleration of 2.85 $m/s^{2}$. Find the action-reaction force pair that involves the pole and calculate these forces.
- Two ice skaters stand on a frictionless ice rink and face each other, each holding the end of a rope. 50.0 kg skater A pulls on the rope, pulling 40.0 kg skater B with a force of 25.0 N.
i. Draw a free body diagram and find the acceleration of skater B.

ii. When skater A pulls on skater B, does skater A accelerate? If so, draw a free body diagram and calculate the acceleration.

###### Free to Join!

StudyPug is a learning help platform covering math and science from grade 4 all the way to second year university. Our video tutorials, unlimited practice problems, and step-by-step explanations provide you or your child with all the help you need to master concepts. On top of that, it's fun — with achievements, customizable avatars, and awards to keep you motivated.

#### Easily See Your Progress

We track the progress you've made on a topic so you know what you've done. From the course view you can easily see what topics have what and the progress you've made on them. Fill the rings to completely master that section or mouse over the icon to see more details.#### Make Use of Our Learning Aids

#### Earn Achievements as You Learn

Make the most of your time as you use StudyPug to help you achieve your goals. Earn fun little badges the more you watch, practice, and use our service.#### Create and Customize Your Avatar

Play with our fun little avatar builder to create and customize your own avatar on StudyPug. Choose your face, eye colour, hair colour and style, and background. Unlock more options the more you use StudyPug.

###### Topic Notes

In this lesson, we will learn:

- Newton's third law of motion
- Explaining physical phenomena using Newton's third law
- Calculations with Newton's second and third laws

__Notes:____Newton's third law__: when one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.- Also stated: "for every action, there is an equal and opposite reaction."

- Each force in action-reaction force pair is located on a different object in the pair. Each force in action-reaction force pair also has the same "type."
- Example: if a wooden block slides across a floor, the floor exerts a force of friction on the block and the block exerts a force of friction that is equal in magnitude but opposite in direction on the floor. The forces in this pair are on different objects (one acts on the block, and the other acts on the floor), and both are the same type of force (friction).

**Newton's Third Law**For object A exerting a force on object B:

$\vec{F}_{A on B} = - \vec{F}_{B on A}$

$\vec{F}_{A on B}:$ force A is exerting on B, in newtons (N)

$\vec{F}_{B on A}:$ force B is exerting on A, in newtons (N)

2

videos

remaining today

remaining today

5

practice questions

remaining today

remaining today