The pile driver and the sledgehammer

Two tools built on the same idea: raise a heavy mass, then let gravity spend the store for you. Neither has a motor at the point where the work is done.

The pile driver and the pile

Figure to be added

Figure 18.11 — a pile driver rig: the crane arm, the heavy hammer raised on the mast, and the pile standing below it ready to be driven into the ground.

Before laying foundations for a building, the pile driver is used to compact loose soil firmly and to sink piles into the ground. A machine raises the heavy hammer up the mast and releases it onto the head of the pile. The higher it is raised, the more potential energy it stores, and the harder it strikes.

The sledgehammer and the wedge

Figure to be added

Figure 18.12 — a person swinging a sledgehammer above their head, with a log standing on end beneath them and a wedge sunk into its top.

The sledgehammer is used for breaking stone and for splitting firewood. An iron wedge is set into the top of the log, and the raised sledgehammer is released onto it.

Potential energy of the raised hammer → Kinetic energy as it falls → Work done driving the wedge in

What the two have in common

In both, the potential energy of the raised mass is converted into kinetic energy, the mass strikes at speed, and the kinetic energy is passed to whatever it hits — the pile, or the wedge that then splits the log.

Height is the setting on both tools

Neither tool has a power dial. Raising the mass higher is the only way to make the blow harder, and that is m g h being used as a control.