Newton's second law
Newtons andra lag
PhysicsLegendary
Discovered 1687 · Isaac Newton
SPARKON03 / 10
Newton's second law
The ideaA total force changes how something moves, and the heavier it is, the less it changes.
F = m · a
Lets you predictKnowing force and mass, where a thing will be later.
Tests usually ask
  • Find the acceleration
  • Braking or friction force
Scan for the full explanation and a practice question.
SPARKON · 03 / 10
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Physics ★ Legendary: one of the biggest ideas in science

Newton's second law

Swedish: Newtons andra lag · Discovered: Isaac Newton, 1687

A total force changes how something moves, and the heavier it is, the less it changes.

F = m · a

Why it works

Push a shopping trolley and it speeds up. Push a full one just as hard and it speeds up less. Newton's law puts a number on that: acceleration equals force divided by mass.

Only the total force counts. If you push forward with 100 N and friction pulls back with 40 N, the force that changes the motion is 60 N.

What it lets you predict

Knowing force and mass, where a thing will be later.

How tests ask about it

  • Find the acceleration
  • Braking or friction force

Try it

A cyclist and bike together weigh 80 kg. The total forward force is 120 N. What is the acceleration?

Show the answer

a = F / m = 120 / 80 = 1.5 m/s².

Connects to

Energy conservationPythagoras' theorem

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