Mechanical advantage and velocity ratio
Design & Technology · GCSE · The School
Mechanical advantage compares load to effort
Mechanical advantage (MA) = load ÷ effort. A system with MA greater than 1 lets a small effort move a bigger load — that is the whole point of a lever, a gear train or a pulley system. MA has no units, since it is one force divided by another; it is simply a ratio, stated as a number.
Velocity ratio compares the distances moved
Velocity ratio (VR) = distance moved by effort ÷ distance moved by load. Whenever a small effort moves a large load, the effort has to travel FURTHER than the load does — VR is always the trade-off that pays for a high MA. Neither force nor distance is created from nothing; one is exchanged for the other.
A worked mechanical advantage calculation
A wheelbarrow lifts a 400 N load using 100 N of effort. MA = 400 ÷ 100 = 4. This means the wheelbarrow multiplies the effort force by four — a genuinely large mechanical advantage for a simple second-class lever, which is exactly why a wheelbarrow makes a heavy load feel manageable.
A worked velocity ratio and efficiency calculation
For the same wheelbarrow, the effort end moves 0.8 m while the load only rises 0.2 m. VR = 0.8 ÷ 0.2 = 4. Efficiency = (MA ÷ VR) × 100 = (4 ÷ 4) × 100 = 100%. A real wheelbarrow is never quite this perfect — friction at the pivot and wheel always takes a small share, so a real efficiency reads a little under 100%.
Why no real system reaches 100% efficiency
Friction between moving parts, and energy lost bending or flexing materials, both turn some input energy into heat instead of useful output. This is why a calculated efficiency of exactly 100% from real measurements should be treated as a rounding artefact, not a triumph — a well-designed system aims to get CLOSE to 100%, never exactly at it.
Reading which value the question actually wants
MA asks about FORCE: how much load for how much effort. VR asks about DISTANCE: how far the effort moves for how far the load moves. Efficiency compares the two. A question asking to "calculate the mechanical advantage" and being answered with a distance ratio, or the reverse, is marked wrong even when the arithmetic is correct — naming which quantity is being found matters as much as the sum itself.