Energy and Forces
What you must understand
Energy exists in forms such as kinetic, potential, thermal, light, sound, electrical and chemical, and is transferred between stores but never created or destroyed. Know the difference between renewable and non-renewable energy sources and give examples. Understand forces as pushes or pulls measured in newtons, including gravity, friction, air resistance, upthrust and magnetism. Know that forces can change an object's speed, direction or shape, and that balanced forces cause no change in motion. Understand simple machines and levers, pressure, and basic electrical circuits with cells, bulbs, switches and conductors and insulators.
Traps that appear in questions
- Saying energy is "used up"; it is transferred or dissipated, often as heat to the surroundings.
- Confusing mass (kg, unchanged) with weight (N, depends on gravity).
- Drawing a series circuit with a gap or missing return path, so the bulb cannot light.
- Believing a moving object needs a continuous force to keep moving; friction, not motion, needs a force.
- Mixing up renewable sources with clean ones; wood is renewable but burning it pollutes.
- Forgetting to name the direction of a force in diagrams.
Rule of thumb and worked example
For circuits: the path must be a complete loop from one terminal of the cell back to the other. For forces: draw arrows for each force and compare them.
Example: A 600 N box is pushed with 200 N while friction is 150 N. The resultant force is 200 − 150 = 50 N in the direction of the push, so the box accelerates. If friction were also 200 N, the forces would be balanced and the box would move at constant speed or stay still.