How are a first-class lever and a wheel and axle similar?

The correct answer highlights a key similarity between a first-class lever and a wheel and axle: both systems rotate about a pivot point and gain mechanical advantage because of the difference in their radii.

In a first-class lever, the fulcrum is positioned between the effort applied and the load being moved. The distance from the fulcrum to where the effort is applied (the effort arm) can be longer than the distance from the fulcrum to the load (the load arm). This difference allows a smaller effort force to lift a heavier load, effectively leveraging the mechanical advantage.

Similarly, in a wheel and axle system, the wheel rotates around the axle, and the radii of the wheel (the larger circle) compared to the axle (the smaller circle) can significantly affect the force required to turn the system. If a force is applied to the edge of the wheel, the mechanical advantage is created because the distance moved at the edge of the wheel is greater than the distance moved at the axle, allowing the system to lift heavier loads or exert more force than the effort applied.

Both systems demonstrate this fundamental principle of mechanical advantage through the strategic positioning of their pivot points and differing radii, making option B the correct choice.