Forces, Motion, Energy and Simple Machines
This domain tests what forces do to motion, the difference between mass and weight, energy transfer, and how simple machines make work easier.
Forces and motion
A force is a push or a pull, measured in newtons with a newton meter. Balanced forces give no change in motion: an object stays still or keeps a steady speed. Unbalanced forces change speed or direction. Friction opposes sliding and is useful in brakes and shoes but wastes energy as heat. Gravity pulls objects towards the centre of the Earth; mass (kg) is the amount of matter, while weight (N) is the pull of gravity, roughly mass × 10. Air resistance and water resistance increase with speed and surface area.
Energy and machines
Energy comes in forms including kinetic, gravitational potential, elastic, thermal, light, sound, chemical and electrical, and is transferred rather than used up. A lever has a pivot (fulcrum), load and effort; moving the effort further from the pivot reduces the effort needed. A pulley changes the direction of a force, an inclined plane spreads effort over a longer distance, and gears transfer turning motion.
Worked example
A 40 kg child sits 1.5 m from the pivot of a see-saw. Where should a 60 kg child sit to balance? Moments must match: 40 × 1.5 = 60, so the second child sits 1.0 m from the pivot.
Traps that cost marks
Do not mix up mass and weight, or write that a force 'runs out'. Never say energy is 'used up' - it is transferred to the surroundings, often as heat. Friction is not always a nuisance.