Newton's Second Law
Net force equals mass times acceleration: F = ma.
About this topic
Newton's second law states that the acceleration of an object is proportional to the net force and inversely proportional to its mass: F = ma. A 1 N force gives a 1 kg mass an acceleration of 1 m/s². Acceleration points in the direction of the net force.
To solve problems, draw a free-body diagram, add the forces as vectors to get the net force, and then divide by mass. Use it separately in the x and y directions. Doubling the force doubles the acceleration, while doubling the mass halves it.
Example: a 1200 kg car is pushed forward by an engine force of 3000 N against 600 N of resistance. The net force is 2400 N, so a = 2400/1200 = 2 m/s². A shopping trolley accelerates more slowly when full, and a small rocket engine can move a light satellite quickly. Engineers use the law in vehicle design, sports science and spaceflight.
Common mistakes: using a single applied force instead of the net force, mixing up mass and weight, and thinking that a large force always means a large velocity. Force produces acceleration, not velocity.
Key ideas
- Acceleration is proportional to force
- Inversely proportional to mass
- Unit: newton = kg·m/s²
Quick check
Use cases: where Newton's Second Law helps
- Homework: review the key idea behind Newton's Second Law before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Newton's Second Law without notes.
- Visual learning: play with the interactive lab to see how Newton's Second Law changes when you adjust its inputs.
- Teaching a friend: explain Newton's Second Law in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Newton's Second Law?
Net force equals mass times acceleration: F = ma.
What will I learn in Newton's Second Law?
Acceleration is proportional to force. Inversely proportional to mass. Unit: newton = kg·m/s².
Is Newton's Second Law part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Newton's Second Law lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Newton's Second Law?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.