Which device is a simple machine that consists of a rigid bar that pivots around a fixed point?

• A. Inclined plane
• B. Lever
• C. Screw
• D. Wheel and axle

Answer: (B)

A lever is a simple machine that uses a rigid bar and a fixed point called the fulcrum. When you push on one end, the bar pivots around the fulcrum and lifts or moves a load on the other end. The distance from the fulcrum to where you apply force (the effort arm) and to the load (the load arm) determines how much force you need and how fast things move. This setup—rigid bar plus a pivot point—defines the lever, like a seesaw or a crowbar. The other devices are different types of simple machines: an inclined plane is a ramp, a screw is an inclined plane wrapped around a cylinder, and a wheel and axle involves rotating wheels around a central axis.