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Forces Hub (Dynamics + Moments)

G3 Physics and O-Level Physics forces hub: Newton's Laws, free body diagrams, friction, terminal velocity, moments, and stability.

  • G3 Pure Physics K323 / retained O-Level Physics 6091
  • 14 lessons
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Before you begin

Follow the lesson route in order when the topic is new. If you are revising, begin with the topic check and return to the lesson it identifies.

How the ideas connect

  1. Forces and free-body diagrams
  2. Resultant force
  3. Moments and equilibrium
  4. Stability

Learn in order

Lesson route

01

Dynamics (Newton's Laws)

  1. 01What is a Force?Contact vs non-contact forces.
  2. 02InertiaHow mass resists change in motion.
  3. 03Weight & GravityGravitational field strength and weight.
  4. 04Free Body DiagramsDrawing forces correctly (arrows from the body).
  5. 05Newton's 1st & 3rd LawsInertia, balanced forces, and action-reaction pairs.
  6. 06Newton's 2nd LawCalculating acceleration from net force (F = ma).
  7. 07FrictionEffects of friction and how to reduce it.
  8. 08Terminal VelocityMotion with air resistance (zero net force).
02

Turning Effects (Moments)

  1. 09Moment of a ForceTurning effect = force × perpendicular distance.
  2. 10EquilibriumConditions for static equilibrium (net force and net moment are zero).
  3. 11Centre of GravityFinding CoG and its role in stability.
  4. 12StabilityStable, unstable, and neutral equilibrium.
03

Graphical Force Skills

  1. 13Adding ForcesFinding the resultant force (parallelogram/triangle method).
  2. 14Forces in EquilibriumClosed vector triangles for 3 balanced forces.

Prove your understanding

Practice and repair

Recommended next stepO Level Forces Hub (Dynamics + Moments) topic checkFind the exact ideas that need another look.Start topic check

Other ways to practise

Key ideas and reference

Use this concise Forces Hub (Dynamics + Moments) checklist for orientation. Open a linked lesson for definitions, derivations, diagrams and worked examples.

  • Contact vs non-contact forces.
  • Turning effect = force × perpendicular distance.
  • Finding the resultant force (parallelogram/triangle method).
  • Closed vector triangles for 3 balanced forces.
Course coverage and review details

This hub groups the reviewed O Level Forces Hub (Dynamics + Moments) lesson route.

G3 Pure Physics and retained O-Level access share this learner route while qualification-specific evidence remains separate.

Reviewed Jul 18, 2026

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Frequently asked questions

What should I study first in O Level Forces?

Start by identifying force types and resultants, then draw free-body diagrams before applying Newton's laws, friction, graphical equilibrium, moments and stability.

Which formulas and definitions must I know?

Apply resultant force equals mass times acceleration, weight equals mass times gravitational field strength, and moment equals force times perpendicular distance. Newton's law statements do not need to be recalled word for word.

What mistakes cost the most marks in this topic?

Common losses come from poor FBDs, mixing action-reaction pairs on the same body, and using non-perpendicular distances in moment calculations.

Should I do quiz or structured practice after this hub?

Take the forces quiz first for quick diagnosis, then do the structured set for longer free-body and moment explanations.