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06252026–2028 syllabus

PHYSICS · CHAPTER 1

Motion, forces and energy

Describe motion quantitatively, explain how forces change it, and account for energy transfers.

Core + Supplement4 connected sectionsSyllabus-aligned guide

LEARNING OBJECTIVES

What you will be able to do

  • measure length, time, mass, volume and density reliably
  • interpret distance–time and speed–time graphs
  • apply force, momentum, work, energy, power and pressure equations
  • explain moments, equilibrium, elasticity and energy conservation

AT A GLANCE

Syllabus0625Coverage2026–2028Sections4LevelCore + Supplement

INTRODUCTION · THE BIG IDEA

Describe motion quantitatively, explain how forces change it, and account for energy transfers.

Mechanics turns movement and interactions into measurable quantities. A graph can describe an entire journey, while a force diagram explains why the motion changes.

The same chapter links everyday machines, collisions and energy resources through conservation laws: momentum and energy are tracked rather than lost without explanation.

01

SECTION 01

Measurement, motion and graphs

Core concept

Use a ruler or tape at eye level, repeat timings where possible, and obtain the volume of an irregular solid by displacement. Speed describes how quickly distance changes; velocity also includes direction.

On a distance–time graph, gradient is speed. On a speed–time graph, gradient is acceleration and area under the graph is distance travelled. A horizontal speed–time line means constant speed, not rest.

RULE 1
speed = distance ÷ time
RULE 2
acceleration = change in velocity ÷ time
RULE 3
distance = area under a speed–time graph
ORIGINAL STUDY DIAGRAMBuild a motion description
1Choose a positive direction
2Record values with units
3Calculate gradient or area
4State speed, velocity or acceleration
Original worked example

Reading a speed–time graph

  1. A car increases speed uniformly from 4 m/s to 16 m/s in 6 s.
  2. Acceleration = (16 − 4) ÷ 6 = 2.0 m/s².
  3. Distance during this interval is the trapezium area: ½(4 + 16) × 6.

Answer: Acceleration = 2.0 m/s² and distance = 60 m.

02

SECTION 02

Mass, weight, density and forces

Core concept

Mass measures the amount of matter and remains constant; weight is the gravitational force on that mass. Density compares mass with volume.

A resultant force produces acceleration in its direction. With zero resultant force, an object remains at rest or moves with constant velocity. Friction and drag oppose motion, while terminal velocity occurs when drag equals weight.

RULE 1
weight = mass × gravitational field strength (W = mg)
RULE 2
density = mass ÷ volume (ρ = m/V)
RULE 3
resultant force = mass × acceleration (F = ma)
Force effects
SituationResultant forceMotion
Balanced forceszerorest or constant velocity
Unbalanced forcesnon-zerovelocity changes
Falling at terminal speeddrag = weightconstant downward velocity
Original worked example

Finding density by displacement

  1. A stone has mass 135 g.
  2. Water rises from 40 cm³ to 90 cm³, so stone volume = 50 cm³.
  3. Density = 135 ÷ 50.

Answer: Density = 2.7 g/cm³.

03

SECTION 03

Moments, deformation and momentum

Core concept

For an object in equilibrium, resultant force and resultant moment are zero. The centre of gravity is the point through which the whole weight may be considered to act; a wider base and lower centre of gravity improve stability.

A spring obeys Hooke's law only up to its limit of proportionality. Momentum is conserved in an isolated collision, although kinetic energy may be transferred to heating, sound or deformation.

RULE 1
moment = force × perpendicular distance
RULE 2
F = kx
RULE 3
momentum = mass × velocity (p = mv)
RULE 4
force = change in momentum ÷ time
Original worked example

Balancing a beam

  1. A 30 N load acts 0.40 m left of a pivot.
  2. Its anticlockwise moment is 30 × 0.40 = 12 N m.
  3. A force acts 0.60 m to the right. For balance, F × 0.60 = 12.

Answer: The balancing force is 20 N.

04

SECTION 04

Energy, work, power and pressure

Core concept

Energy stores include kinetic, gravitational, elastic, chemical, thermal, nuclear, magnetic and electrostatic. Energy is transferred mechanically, electrically, by heating or by radiation, while total energy is conserved.

Useful output is always less than or equal to total input. Renewable resources can be replenished; non-renewable fuels are finite. Pressure increases when force is concentrated over a smaller area, and liquid pressure increases with depth and density.

RULE 1
kinetic energy = ½mv²
RULE 2
change in gravitational potential energy = mgΔh
RULE 3
work done = force × distance
RULE 4
power = work done ÷ time
RULE 5
efficiency = useful output ÷ total input × 100%
RULE 6
pressure = force ÷ area
RULE 7
liquid pressure change = ρgΔh
Original worked example

Efficiency of a lifting motor

  1. A motor lifts 240 kg through 5.0 m using 16 000 J of electrical energy.
  2. Useful energy = mgh = 240 × 10 × 5.0 = 12 000 J.
  3. Efficiency = 12 000 ÷ 16 000 × 100%.

Answer: Efficiency = 75%.

QUICK CHAPTER SUMMARY

The ideas to carry forward

  • Graph gradients and areas reveal motion quantities.
  • A non-zero resultant force changes velocity.
  • Moments, momentum and energy are powerful conservation tools.
  • Every numerical answer needs a suitable unit and sensible precision.

QUICK REVISION CHECKLIST

Can you do each of these without your notes?

  • measure length, time, mass, volume and density reliably
  • interpret distance–time and speed–time graphs
  • apply force, momentum, work, energy, power and pressure equations
  • explain moments, equilibrium, elasticity and energy conservation
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