Ramp & wedge

How do you get a fridge onto a moving van when nobody can heave it up? You lean a board against it and push. The inclined plane may be humanity's oldest machine, even the pyramid builders dragged their stone blocks up ramps. Its trick is simple and brilliant: it turns a steep lift into a long, shallow push.

Same work, longer path

Whether you heave a crate straight up or push it along a ramp, at the top it holds the same lifting work: weight times height. The ramp, however, spreads that work over a longer path. If the ramp is three times as long as the height, you need only a third of the force without friction, because $F \cdot s = G \cdot h$. The shallower the ramp, the smaller the force and the longer the path.

Hairpin roads: ramps in the mountains

A mountain road could run straight up the slope, but then every engine would fight an enormous gradient. Instead the road winds in hairpins: 2 km as the crow flies become 12 km of driving, and in return the gradient drops to a sixth. Gradients are given in percent, that is height difference divided by length of road, times 100. A sign saying 8 percent therefore means the road climbs 8 m over 100 m. Cyclists, locomotives and loaded trucks all use the same trade, small force over a long path instead of large force over a short one.

The wedge: a travelling ramp

Flip the inclined plane over and drive it into a material, and it is called a wedge. An axe head is exactly that: the blow drives the wedge a short way into the wood, and the shallow flanks push the fibres apart with multiplied force. The sharper the wedge, the greater the advantage. Knives, nails, drawing pins and even your front teeth work on the wedge principle.

The screw: a ramp wound up

Wrap a paper triangle around a pencil and you will see a screw thread appear. A screw is a ramp wound around a cylinder. Each turn moves it forward only by the thread pitch, often just a millimetre, while your hand on the screwdriver covers many centimetres of circumference. This huge advantage makes clamps and screw jacks so strong. And because the thread rises so gently, friction inside it jams the screw in place, so it does not turn back out on its own.