Unit 1: How Is Energy Useful to Society?
Core concepts
Unit 1 links motion, energy and heat to the technologies society relies on. You must be able to describe motion using displacement, velocity and acceleration; interpret position–time and velocity–time graphs; and apply the constant-acceleration equations to straight-line motion. Distinguish scalars (distance, speed) from vectors (displacement, velocity). For energy, know kinetic energy, gravitational potential energy near Earth, work, and conservation of mechanical energy, plus power as the rate of energy transfer.
Heat is a separate idea: temperature measures average kinetic energy, while heat is energy transferred because of a temperature difference. Understand specific heat capacity, latent heat of fusion and vaporisation, and the three transfer modes - conduction, convection and radiation. For electricity, know current, voltage, resistance and Ohm's law, and how simple series and parallel circuits behave.
Traps examiners set
- Mixing distance and displacement when calculating average speed versus average velocity.
- Assuming a horizontal section of a velocity–time graph means the object is stationary - it means constant velocity.
- Forgetting that during a phase change, temperature stays constant while latent heat is absorbed.
- Adding resistances directly in parallel circuits.
- Using g = 9.8 m s⁻² but neglecting to state the direction of weight.
Worked example
A 0.50 kg ball is released from rest 2.0 m above the ground. Ignoring air resistance, find its speed just before impact.
Conservation of energy: mgh = ½mv². The mass cancels: v = √(2gh) = √(2 × 9.8 × 2.0) = √39.2 ≈ 6.3 m s⁻¹. Note the mass is irrelevant unless friction is involved, and always check units.
Rule of thumb
Before substituting numbers, sketch the situation, list knowns with units, and identify which conservation law applies.