An inclined plane is any slope or ramp, like a wheelchair ramp or a slide. The ramp makes it easier to lift something heavy, like a rock. Instead of lifting the rock straight up, you can push it a greater distance, but with less force. The amount of work remains the same. Work is force x distance. So if you increase the distance the rock moves, you can decrease the amount of force you need.
What if you make the ramp steeper? Then you’ll have a shorter distance. But it will be harder to push the rock. (You’ll need more force). What if you make the ramp less steep? Then it will have to be longer. But it will be easier to push the rock. Either way, it’s the same amount of work in the end. But you have the choice of doing easier work for a longer time, or harder work for a shorter time.
We call it an “inclined plane” because it is a plane – a flat surface – and it is inclined – sloped, not level. Inclined planes also let you control how fast something goes downhill. Objects fall faster on a steeper ramp. You could just drop the thing, and let gravity pull it to earth. But maybe you’d like to go slower. Maybe you enjoy the speed from going down a slide, but you might break your arm if you just fell from the top of the slide straight down.
All kinds of animals use inclined planes when they choose their path up or down a steep hill, and ants, for example, also use inclined planes in building their anthills. People have used inclined planes since even before they were people, about 200,000 years ago. By the time of Old Kingdom Egypt, about 2500 BC, people were building their own earth ramps to move heavy stones for the Pyramids. The first staircases (a kind of inclined plane, because stairs make it easier to go up than if you had to jump) also go back to the Bronze Age.