Part 02 · Newton's laws and forces · Card 3 of 10
Newton's second law
Net force equals mass times acceleration (F = ma). The same push gives a small mass more acceleration.
Last updated
Analogy
Pushing an empty shopping trolley versus a full one.
Example
Car acceleration
a = F / ma = 3000 N / 1200 kga = 2.5 m/s^2
In practice
A 1200 kg car with a 3000 N net force accelerates at 2.5 m/s squared.
Practice
Flashcards
- What does Newton's second law say?Net force equals mass times acceleration (F = ma).
- What is the SI unit of force?The newton (N), equal to 1 kg m/s^2.
Interview questions
- Explain Newton's third law using a rocket in space.
- Engine pushes gas backward
- Gas pushes rocket forward with equal force
- Forces act on different objects, so rocket accelerates
Questions people ask
Does your mass change on the Moon?
Mass is the amount of matter in an object, measured in kilograms, and it never changes. Weight is the gravitational force on that mass, measured in newtons. An astronaut keeps the same mass on the Moon but weighs about six times less there.
Why does F = ma use net force?
Acceleration depends on the combined effect of all forces, not on any single one. If you push a box with 10 N but friction pulls back with 10 N, the box does not accelerate. Always add all the forces first, then divide by mass.