# Motion, Forces and Energy

> CIE IGCSE Physics · CIE IGCSE Physics (0625)
> Source: https://www.owlsprep.com/study/cie-0625-u1-overview/
> Weight: 15-20% of both MCQ (Papers 1/2) and Theory (Papers 3/4) sections

This unit covers core foundational physics concepts from measurement and motion to forces, energy and pressure, forming the base for all subsequent IGCSE Physics topics including thermal physics, waves and electricity.

**Prerequisites:** Basic secondary school numeracy and general science knowledge

## Learning objectives

- Use SI units, prefixes and standard measurement techniques correctly for core physical quantities
- Analyse linear motion using speed, velocity, acceleration and motion graph interpretation
- Apply force concepts including Newton’s laws, moments, momentum and pressure to solve quantitative problems
- Calculate work, energy transfer, power and efficiency for physical and engineered systems
- Distinguish between mass, weight and density, and perform related calculations for all states of matter

## Unit at a glance

The unit follows a logical learning sequence: it opens with foundational measurement skills, moves to descriptions of linear motion, explores the forces that change motion, then covers energy transfer, energy resources, and pressure in solids and fluids. Extended-only content is clearly marked for students taking the higher-tier syllabus.

Concepts build incrementally, so work through subtopics in the listed order to avoid gaps in understanding, and reference the unit cheatsheet for quick cross-subtopic formula reminders.

Work through the following subtopics in order to build your knowledge step-by-step:
- [Physical Quantities and Measurement Techniques](https://www.owlsprep.com/study/cie-0625-u1-physical-quantities-and-measurement-techniques/) — Learn SI units, prefixes, and practical measurement methods for length, time, volume and mass.
- [Speed, Velocity and Motion Graphs](https://www.owlsprep.com/study/cie-0625-u1-speed-velocity-and-motion-graphs/) — Calculate speed, velocity and acceleration, and interpret distance-time and velocity-time graphs for linear motion.
- [Mass, Weight and Density](https://www.owlsprep.com/study/cie-0625-u1-mass-weight-and-density/) — Distinguish between mass and weight, and calculate density of regular, irregular and fluid substances.
- [Forces, Elasticity and Newton's Laws](https://www.owlsprep.com/study/cie-0625-u1-forces-elasticity-and-newton-s/) — Identify types of forces, explore elastic deformation, and apply Newton's three laws of motion to solve problems.
- [Moments and Centre of Gravity](https://www.owlsprep.com/study/cie-0625-u1-moments-and-centre-of-gravity/) — Calculate turning moments of forces, analyse equilibrium systems, and locate centre of gravity for regular objects.
- [Momentum and Impulse (Extended Only)](https://www.owlsprep.com/study/cie-0625-u1-momentum-and-impulse/) — Calculate linear momentum and impulse, and apply the principle of conservation of momentum to collisions.
- [Energy, Work and Power](https://www.owlsprep.com/study/cie-0625-u1-energy-work-and-power/) — Identify forms of energy, calculate work done, power output, and energy transfers between systems.
- [Energy Resources and Efficiency](https://www.owlsprep.com/study/cie-0625-u1-energy-resources-and-efficiency/) — Evaluate renewable and non-renewable energy resources, and calculate energy efficiency of systems.
- [Pressure](https://www.owlsprep.com/study/cie-0625-u1-pressure/) — Calculate pressure in solids, liquids and gases, and apply the hydraulic pressure principle to real systems.

## Common pitfalls

- **Wrong:** Confusing mass and weight in force calculations
  - Why it fails: Mass is a scalar measure of matter in kg, while weight is a gravitational force measured in Newtons
  - Correct: Always convert mass to weight using $W = mg$ when calculating forces involving gravity
- **Wrong:** Mixing up distance-time and velocity-time graph gradients
  - Why it fails: Gradient of a distance-time graph is speed, while gradient of a velocity-time graph is acceleration
  - Correct: Label graph axes first before interpreting gradients or areas under curves
- **Wrong:** Using force alone to calculate work done
  - Why it fails: Work done requires both force and the distance moved in the direction of the applied force
  - Correct: Use $W = F \times d$, ensuring $d$ is the distance parallel to the applied force

## Cheatsheet

| Concept/Formula | Relevant Subtopic | Key Note |
| --- | --- | --- |
| $v = \frac{\Delta d}{\Delta t}$ | Speed, Velocity and Motion Graphs | Average speed = change in distance / change in time |
| $W = m \times g$ | Mass, Weight and Density | Weight = mass × gravitational field strength ($g≈9.8$ N/kg on Earth) |
| $\rho = \frac{m}{V}$ | Mass, Weight and Density | Density = mass / volume, units kg/m³ or g/cm³ |
| $F = m \times a$ | Forces, Elasticity and Newton's Laws | Resultant force = mass × acceleration |
| $M = F \times d$ | Moments and Centre of Gravity | Moment of a force = force × perpendicular distance from pivot |
| $p = m \times v$ | Momentum and Impulse (Extended Only) | Momentum = mass × velocity, conserved in closed systems |
| $W = F \times d$, $P = \frac{W}{t}$ | Energy, Work and Power | Work done = force × distance; Power = work done / time |
| $P = \frac{F}{A}$, $P = \rho g h$ | Pressure | Pressure = force / area; Pressure in liquid = density × g × depth |

## What's next

Start your study of this unit with the first subtopic on physical quantities and measurement techniques, as these foundational skills are required for all subsequent calculations and practical activities in this unit and later IGCSE Physics content. Once you complete all subtopics in Unit 1, you will move on to Unit 2 covering Thermal Physics, which builds on the energy concepts you will learn here. Test your understanding with end-of-subtopic quizzes before progressing to more advanced content.

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From [OwlsPrep](https://www.owlsprep.com) — free study guides for A-Level, IB, AP and IGCSE, written against the official syllabus. Canonical page: https://www.owlsprep.com/study/cie-0625-u1-overview/