Go ahead – hit it hard!
A simple stack of blocks demonstrates that an object at rest will remain at rest, unless a force causes it to move.

5 or 6 wooden blocks, each about 13 cm (5 in.) long, cut from a relatively smooth-surfaced two-by-four
meter stick

1. Stack the blocks neatly with the large sides parallel to tabletop.2. [...]

Let us suppose that a heavy rock must be lifted, and we find that we are unable to do it by hand. By the use of a strong beam or a crowbar (a strong steel bar) in the way indicated in the diagram, the lifting is accomplished with little difficulty.

The bar constitutes a lever; the [...]