# How does a jackhammer work?

#### How does a jackhammer work?

A jackhammer (or pneumatic hammer) uses compressed air to drive a metal piston up and down inside a cylinder. Each time the piston nears the top of the cylinder, it opens a valve that allows compressed air to flow above it and push it downward. Each time the piston reaches the bottom of the cylinder, it opens a valve that allows compressed air to flow below it and push it upward. Thus the compressed air makes the piston shuttle up and down very rapidly.

But while the piston rebounds gently from a cushion of air at the top of the cylinder, it collides suddenly with a metal bar at the bottom of the cylinder. That metal bar is the top end of the drill bit that the jackhammer uses to cut into pavement. Each time the piston moves downward, it pounds the drill bit a little farther into the pavement. The enormous force that pushes the bit into cement comes from the enormous force needed to stop the descending piston and to accelerate it upward. The drill bit pushes up on the piston very hard and the piston pushes down on the drill bit very hard. These two forces are equal and opposite, as they must be (Newton’s third law of motion.) The piston ends up moving upward and the drill bit ends up moving downward.