Rule of thumb · PhysicsNº 71 / 131

A ramp saves force, never energy

A ramp divides the force by up to 1 over sin(theta), and multiplies the distance by exactly the same factor. The work is unchanged — and once friction is involved a ramp actively costs energy, the more so the gentler it is.

Why it works

People reach for a ramp expecting it to make a job smaller, when what it does is spread the same job over a longer push. That is usually the right trade, because the binding constraint is the force a person or a motor can apply rather than the total energy. But it explains why a long shallow ramp feels endless: at a 1:12 accessibility gradient with ordinary friction, under a third of the effort is going into height and the rest into rubbing.

When it fails

It is a statement about ideal mechanics, and real ramps are chosen for other reasons entirely — what a wheelchair can climb, what a trolley will tip over at, what fits the space. It also ignores that a ramp lets you move a load you simply could not lift, which is not an efficiency question at all.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

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Does a ramp save you work?

A ramp divides the force by up to 1 over sin(theta), and multiplies the distance by exactly the same factor. The work is unchanged — and once friction is involved a ramp actively costs energy, the more so the gentler it is. People reach for a ramp expecting it to make a job smaller, when what it does is spread the same job over a longer push.

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