Newton's Second Law (Cambridge (CIE) IGCSE Physics)

Newton's second law

• Newton's second law of motion states:

The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the object's mass

• Newton's second law of motion explains what happens when a non-zero resultant force acts on an object

• A resultant force occurs when the forces acting on an object are not balanced

• A resultant force acting on an object will cause a change in the object's motion

• This change in motion is an acceleration:

  • Speeding up

  • Slowing down

  • Changing direction

• If the resultant force on an object is not zero, the object will accelerate in the direction of the resultant force

• The bigger this resultant force, the larger the acceleration

• For a given force, the greater the object's mass, the smaller the acceleration experienced

Examples of Newton's second law

Objects like baseballs and lawnmowers accelerate when a resultant force is applied on them. The size of the acceleration is proportional to the size of the resultant force

Calculations using Newton's second law

Extended tier only

• Newton's second law can be expressed as an equation:

• Where:

  • F = resultant force on the object, measured in newtons (N)

  • m = mass of the object, measured in kilograms (kg)

  • a = acceleration of the object, measured in metres per second squared (m/s²)

• The acceleration occurs in the same direction as the resultant force

Formula triangle for acceleration, mass and resultant force

To use a formula triangle, simply cover up the quantity you wish calculate and the structure of the equation is revealed

• A more detailed explanation of how to use formula triangles is covered in the revision note Speed and velocity