Movers push heavy boxes up a ramp into a truck instead of lifting them straight up. The ramp is an inclined plane.
Key idea
An inclined plane (ramp) lets you raise a load with a smaller push, but along a longer path. A wedge is two ramps back to back: it splits or cuts (an ax, a knife, a doorstop). A screw is a ramp wrapped around a post.
Why it works
Lifting a box 1 meter straight up takes a big force over a short path. Pushing it up a 4-meter ramp to the same height takes about a quarter of the force (plus a bit for friction), over four times the path.
Worked example: Long or short ramp?
Ramp A is 2 meters long, ramp B is 6 meters long. Both reach the same truck. Which needs less push?
- Both raise the box the same height.
- The longer ramp spreads the work over a longer path.
Answer: Ramp B, the longer one, needs less push.
Mountain roads zig-zag for the same reason: a longer, gentler path is easier to climb. A jar lid and a corkscrew are screws.
Common mistake
Thinking the longer ramp is harder because it is longer. Each step is easier; there are just more of them.
Try it at home
- Tie a string to a toy car with a few coins taped on, and hook a rubber band to the string.
- Pull it straight up to a stack of books, then up a ramp to the same stack. Watch how far the rubber band stretches each time.
- Less stretch means less force.
Going further. Simple Machines in Physical Science explains the numbers.