This topic covers how a force transfers energy by doing work, how energy sits in different stores, how to measure how well a device uses energy, and how to explain energy loss in words. It connects forces, motion and every device question in IGCSE Physics.
Exact wording and required items change between syllabus years, so check the current Cambridge IGCSE Physics 0625 page for your exam year. This page follows the general skills. The Physics learning guide shows where the topic sits in the whole subject.
What do I need to know first?
You need weight from mass, W = mg, which is covered in mass, weight and density, and the idea of a force from forces and momentum. Core maths is enough: multiplying decimals, rearranging a simple formula, squares and square roots, and percentages.
One worked example that uses the whole topic
A 2.0 kg book is lifted steadily from a table to a shelf 1.5 m higher. Take g = 10 N/kg. (Invented example data.)
Work: the force equals the weight, 2.0 × 10 = 20 N. Work done = 20 × 1.5 = 30 J.
Store: the 30 J is transferred to the book’s gravitational potential store.
Falling: if the book falls back and air resistance is ignored, it gains 30 J of kinetic energy. From KE = ½mv², 30 = ½ × 2.0 × v², so v² = 30 and v = 5.5 m/s.
Efficiency: suppose the pulley system used to lift it took in 40 J. Efficiency = 30 ÷ 40 = 0.75, or 75%, and 10 J was wasted to the thermal store.
Explanation: the 10 J was transferred to thermal stores of the pulley and surroundings by friction. It did not disappear.
In what order should I study the lessons?
- Distinguish energy transfer from force. Start here, because confusing N with J spoils everything later.
- Calculate work along a displacement. This gives you W = Fd and unit handling.
- Track energy stores in a simple system. It adds GPE and KE and the idea of conservation.
- Calculate efficiency with consistent quantities. It needs useful output, so it follows the stores.
- Explain an energy loss without saying energy disappears. It turns your calculations into marked sentences, so it comes last.
Then use the work, energy and efficiency practice set to test all five together.
What traps catch students?
- Mixing N and J. A force is not an energy transfer.
- Forgetting to square the speed in kinetic energy.
- Using mass as the force when calculating work for lifting.
- Dividing joules by kilojoules in an efficiency calculation.
- Writing “energy is lost or used up” instead of naming the store it was transferred to.
How do I use the practice set well?
Attempt it after you have worked through the lessons, not while reading them. Write units in every answer, then check the worked solution. The set ends with a table that sends each error type back to the right lesson.
Next in the subject, power and energy resources uses energy per second. Learners who want the routine explained by a teacher can look at online one-to-one Physics tuition.