How Does a Ramp Work? The Inclined Plane and the Longer Path

A ramp beside the stairs

Look at the front entrance of many schools, libraries and community centres. Beside the stairs, there is often a long ramp that zigzags back and forth or stretches along the wall. Both paths reach the same door. So why is the ramp so much longer?

An inclined-plane activity sheet published on the RAFT website points out the same thing: a wheelchair ramp is much longer than a staircase that is needed to reach the same height. That extra length is not a mistake. It is how the ramp does its job.^[3]

What is an inclined plane?

Britannica describes an inclined plane as a simple machine consisting of a sloping surface, used for raising heavy bodies. The word plane means a flat surface, and inclined means tilted. Put them together and you get a tilted flat surface: a ramp.

The RAFT sheet calls the inclined plane the simplest simple machine. It has no moving parts at all. In the Daily Read lessons on levers and pulleys, you met machines with a bar or a wheel. A ramp just sits there, yet it can still make a hard job easier.^[1]

Push up the slope instead of lifting straight up

Imagine a heavy box of library books on the floor and a stage 1 metre high. You could lift the box straight up. To do that, your arms must hold up the whole weight of the box.

Now lay a ramp from the floor to the stage and slide or roll the box up it. Britannica explains that, without friction, moving an object up an incline takes less force than lifting it straight up. The ramp holds up part of the weight while you push, so your arms only supply the rest.^[1]

Steep or gentle: the trade-off

Energy Education, an online science encyclopedia, says that the longer the plane gets, the easier the task will be in terms of force. It also says the distance will always have to change in proportion. A gentler ramp means a smaller push, but you have to push the box farther.

Britannica describes the other end: the steeper the slope, the more nearly the required force approaches the actual weight. A ramp so steep that it stands straight up is no help at all; you are back to lifting.

Here is an invented example with ideal numbers. A ramp 2 metres long up to a 1-metre stage needs a push of about half the box's weight, and the box travels 2 metres. A ramp 4 metres long to the same stage needs about one quarter of the weight, and the box travels 4 metres. Energy Education gives the rule for an ideal ramp as the length divided by the height. It is the same deal you met with levers and pulleys: win on force, pay with distance.^[2]

Friction takes its share

Real ramps are not perfect. When a box rubs against a ramp, friction pushes back against the motion. Energy Education says friction is always present, so the true mechanical advantage of a ramp will always be less than the ideal one. In plain words, the real push is a little bigger than the numbers in the invented example.

That is one reason people put wheels on heavy things before pushing them up a ramp. A cart or a dolly rolls instead of scraping, so less of the push is wasted.^[2]

Ramps hiding in plain sight

Energy Education describes lifting a boat out of the water onto higher land. Lifting it straight up would be a daunting task, but pulling it up a ramp takes less force over a much longer pull. The same page says stairs are really a form of ramp, broken into steps.

Britannica adds that the inclined plane idea is used widely, including in screws and bolts, where a small turning force along a slope can produce a much larger force. A screw is like a ramp wrapped around a post. Next time you see a ramp, ask two questions: How high does it rise, and how long is it? The longer it is for the same height, the smaller the push.^[2]