9.3 Simple Machines & Magnetism

9.3 Simple Machines & Magnetism

A simple machine is a device that makes a job easier by changing a force — either its size (a small effort moves a big load) or its direction (you pull down, the load goes up). The trade at the heart of every machine is force for distance: use a smaller force, and you must move it through a longer distance. A long, gentle ramp lets you push a heavy box up with less force than lifting it — but you walk much further. Nothing is free; the machine just swaps the terms to suit you. Paper A (Year 3) already asks students to select the most efficient machinery to achieve an outcome, and the idea keeps reappearing right through the senior papers.

The Six Simple Machines

Levers deserve a closer look because ICAS loves them. The force you apply is the effort, and what you move is the load. Where the fulcrum sits decides the lever's behaviour: put the fulcrum closer to the load and a small effort can lift a heavy load, as with a crowbar under a rock. A wheelbarrow puts the load between the fulcrum and the effort, while a fishing rod puts the effort between the fulcrum and the load, trading force for a bigger, faster movement of the rod tip.

Choosing the Most Efficient Machine

Paper A's machinery questions describe a job, offer several candidate machines, and ask which achieves the outcome most efficiently — that is, with the least wasted effort or energy for that particular task. Read the job precisely. To raise a heavy piano into a truck, a ramp beats lifting because it spreads the force over a distance. To raise a flag to the top of a pole, a pulley wins because it lets you pull downwards while standing safely on the ground. To split firewood, only a wedge — the axe head — will do. Efficiency is always about matching the machine's strength to the outcome wanted; the biggest or most complicated machine is rarely the correct answer.

Machines Working Together

Real devices combine several simple machines at once, and spotting the parts is a favourite senior-paper question. A pair of scissors is two levers sharing one fulcrum, with two wedges (the blades) doing the cutting. A bicycle packs in wheels and axles, levers (the pedals, handlebars and brake levers) and gears, all turning your leg force into smooth forward motion against friction and air resistance. When a stimulus shows an unfamiliar gadget, do not panic — break it into parts, name the simple machine each part behaves like, and reason from there.

Gears

Gears are toothed wheels that mesh so that turning one turns the next. Two rules cover school-level questions. First, meshed gears spin in opposite directions. Second, size controls the trade: a large gear driving a small gear makes the small one spin faster but with less force, while a small gear driving a large one makes it spin slower but with more force. Your bicycle uses both arrangements: a big front gear with a small rear gear for speed on the flat, and the reverse combination for grinding up a hill.

Magnetism

Every magnet has a north pole and a south pole, and the pole rule is simple: unlike poles attract, like poles repel. North–south pull together; north–north push apart. Only a few materials are magnetic — iron and steel (which is mostly iron), nickel and cobalt. Aluminium cans, copper wire, plastic, wood and glass are all non-magnetic, which is a classic sorting question. Magnetic force is a non-contact force and works through many materials: a magnet can drag a paperclip across a table through a sheet of paper or a thin book, although the pull weakens quickly as the gap grows.

An electromagnet is a coil of wire, usually wrapped around an iron core, that becomes magnetic only while an electric current flows. That on–off switch is its superpower: scrapyard cranes lift cars with the current on and drop them with the current off, and doorbells and electric motors rely on the same trick. An electromagnet grows stronger with more coils of wire or a larger current — two variables ICAS can easily put into a fair-test question. Finally, a compass is just a small magnet free to swing, and it points north because the Earth itself acts like a giant bar magnet, with a magnetic pole near each geographic pole — a non-contact force big enough to have guided sailors across oceans.