What is a device that reduces the effort needed to perform work and can magnify applied force called?

A device that reduces the effort needed to perform work and can magnify applied force is known as a simple machine. Simple machines are fundamental mechanical devices that provide a mechanical advantage, allowing a smaller input force to produce a larger output force. Examples of simple machines include levers, inclined planes, pulleys, screws, and wedges.

These devices work by changing the direction of the applied force or by spreading the force over a longer distance, thereby making tasks easier to perform. For instance, a lever allows a person to lift a heavy object with less effort by applying force at a distance from a fulcrum.

The other options provided refer to different concepts. A complex machine consists of multiple simple machines working together, whereas a compound machine also combines several simple machines but is often more complex in design. The term mechanical system can refer to any arrangement of components that use mechanical means to perform tasks, but it does not specifically denote a device that principally reduces effort like a simple machine does.