Dynamics
Balanced and unbalanced forces, two-dimensional free-body diagrams, F = ma, friction and action–reaction pairs.
Learning goals
- Draw free-body diagrams for force systems in at most two dimensions
- Describe the effect of balanced and unbalanced forces on a body
- Describe ways a force may change motion
- Identify action–reaction pairs on interacting bodies
- Apply resultant force = mass × acceleration
- Explain the effects of friction on motion
G3 Science (Physics) · Topic 4
Work through the lessons in order, then take the topic check to find the force models that need another look and practise them.
Before you begin
Build the idea in order
- Forces on one body
- Resultant force
- F = ma
- Friction and force pairs
Lessons
Free-body diagrams
Balanced and unbalanced forces, two-dimensional free-body diagrams, F = ma, friction and action–reaction pairs.
Resultant force and balanced motion
Balanced and unbalanced forces, two-dimensional free-body diagrams, F = ma, friction and action–reaction pairs.
Newton's second law
Balanced and unbalanced forces, two-dimensional free-body diagrams, F = ma, friction and action–reaction pairs.
Friction and resistive effects
Balanced and unbalanced forces, two-dimensional free-body diagrams, F = ma, friction and action–reaction pairs.
Newton's third-law interaction pairs
Balanced and unbalanced forces, two-dimensional free-body diagrams, F = ma, friction and action–reaction pairs.
Check your understanding
Dynamics topic check
Check the required topic capabilities and get focused practice for ideas that need another look.
What to remember
- Zero resultant force means zero acceleration: an object stays at rest or continues at constant velocity.
- A free-body diagram shows only forces acting on the named object, including forces in up to two dimensions.
- Use F = ma with the resultant force, not one force selected from the diagram.
- An action–reaction pair is equal and opposite but acts on two different interacting bodies.
- Friction opposes relative motion or the tendency for surfaces to slide.
Topic and syllabus information
Dynamics is Topic 4 in K326 / K327 Physics component · 2027.
The lesson and questions stay at the depth required for this course.
Reviewed 9 Aug 2026
Course and syllabus information
- Course
- SEC G3 Combined Science Physics component
- Edition
- SEC G3 Combined Science Physics component 2027