MathsGradeUp logoMathsGradeUp
PhysicsGCSEAQA & EdexcelYears 10–11

GCSE Physics Forces Notes

A force is a push or a pull. Understand resultant forces and Newton's three laws and you can explain and calculate how any object moves.

Practise this topic free Ask Study Coach

Key concepts

Force
A push or pull on an object, measured in newtons (N). Forces can be contact (friction, normal, tension) or non-contact (gravity, magnetism, electrostatic).
Resultant force
The single force that has the same effect as all the forces acting. If it is zero, the object stays still or moves at constant velocity.
Weight vs mass
Mass (kg) is the amount of matter; weight (N) is the force of gravity on that mass: W = mg.
  • A resultant force of zero means the object is in equilibrium (balanced forces).
  • Weight acts from the object's centre of mass.
  • Scalars have size only (mass, speed); vectors have size and direction (force, velocity, acceleration).

Key formulas

Newton's second law

F = m × a

resultant force (N) = mass (kg) × acceleration (m/s²).

Weight

W = m × g

g = 9.8 N/kg on Earth.

Momentum

p = m × v

momentum (kg·m/s) = mass × velocity.

Required practicals

  • Investigate the relationship between force, mass and acceleration using a trolley and light gates.
  • Investigate the extension of a spring with added force (Hooke's law).

Worked example

A resultant force of 30 N acts on a 6 kg trolley. Find its acceleration.

  1. 1Write the equation: F = m × a.
  2. 2Rearrange for a: a = F ÷ m.
  3. 3Substitute: a = 30 ÷ 6.
  4. 4Calculate: a = 5 m/s².

Answer: a = 5 m/s²

Common mistakes

✗ Confusing mass (kg) with weight (N).

✓ Mass is matter and never changes; weight is a force and depends on gravity: W = mg.

✗ Using a single force instead of the resultant in F = ma.

✓ F must be the resultant (net) force acting on the object.

✗ Treating vectors as scalars.

✓ Give direction for forces, velocities and accelerations.

Quick check

Try these, then reveal the answers.

What is the resultant force on an object moving at constant velocity?Reveal answer

Zero.

Find the weight of a 5 kg mass. (g = 9.8 N/kg)Reveal answer

W = 49 N

State Newton's second law as an equation.Reveal answer

F = m × a

Practise more questions with Study Coach feedback

Exam tips

  • Draw a free-body diagram and label every force before you calculate.
  • Check whether a quantity is a vector — if so, state the direction.
  • Rearrange F = ma before substituting to protect the method mark.

Related practice

Practise this topic

Exam-style questions with instant Study Coach feedback.

Flashcards

Quick-fire recall to lock in the key facts.

Worksheets

Printable practice you can work through offline.

Past papers

Full papers with examiner-grade marking.

Study Coach

Ask for a step-by-step explanation any time.

All Physics

Every Physics topic across every exam board.

Related topics

Newton's Laws of MotionSpeed, Velocity & Acceleration

Key terms explained

Short, exam-ready definitions with a formula, a worked example and an examiner tip.

What is resultant force?Full glossary

Frequently asked questions

What is the difference between mass and weight?+

Mass is the amount of matter in kilograms and is the same everywhere; weight is the gravitational force on that mass in newtons and changes with gravitational field strength.

What does a resultant force do to an object?+

A non-zero resultant force causes acceleration (speeding up, slowing down or changing direction); a zero resultant force means constant velocity or rest.

Create a free account to practise forces with Study Coach feedback

Try 5 questions now, get instant examiner-grade marking and ask the Study Coach to explain anything. Free during our early launch period — no credit card required.

Create free account Try the Study Coach

Related on MathsGradeUp

Keep studying

Practise it