Newton's Laws of Motion
Isaac Newton's three laws of motion describe the relationship between forces and movement. They explain everything from how rockets launch to why we wear seatbelts, and are foundational to physics and engineering.
What You Need to Know
Key Concept Diagram
Newton's 1st Law (Inertia): an object at rest stays at rest, and an object in motion stays in motion, unless acted on by a net external force
Newton's 2nd Law: Force = mass x acceleration (F = ma); larger force or smaller mass means greater acceleration
Newton's 3rd Law: for every action there is an equal and opposite reaction
Net force: the overall force on an object after all forces are combined
Balanced forces produce no acceleration; unbalanced forces cause acceleration
Key Vocabulary
Inertia
The tendency of an object to resist changes to its state of motion; related to mass
Net Force
The overall force on an object, found by adding all individual forces (considering direction)
Acceleration
The rate of change of velocity; caused by a net (unbalanced) force
Newton's Third Law
For every action force there is an equal and opposite reaction force
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
A book sits on a table. According to Newton's First Law, the book will:
Question 2
A force of 20 N acts on a 4 kg object. What is the acceleration?
Question 3
A swimmer pushes against the wall of a pool and moves away from it. Which law explains this?
Key Concepts Summary
- ●Newton's 1st Law (Inertia): an object at rest stays at rest, and an object in motion stays in motion, unless acted on by a net external force
- ●Newton's 2nd Law: Force = mass x acceleration (F = ma); larger force or smaller mass means greater acceleration
- ●Newton's 3rd Law: for every action there is an equal and opposite reaction
- ●Net force: the overall force on an object after all forces are combined
- ●Balanced forces produce no acceleration; unbalanced forces cause acceleration