Which of the following devices is best described as a compound machine made up of several simple machines working together?

Introduction / Context:

This question comes from basic mechanics and simple machines. A simple machine is a basic mechanical device that changes the magnitude or direction of a force, such as a lever, wheel and axle, inclined plane, pulley, screw, or wedge. A compound machine combines two or more simple machines into a more complex device. Identifying a compound machine helps students connect simple principles to real life objects.

Given Data / Assumptions:

• We consider screw, knife, bicycle, and ramp as examples of mechanical devices.
• Simple machines include lever, inclined plane, wheel and axle, screw, wedge, and pulley.
• A compound machine must contain more than one of these simple machines working together.

Concept / Approach:

A screw is itself a simple machine based on an inclined plane wrapped around a cylinder. A knife is an example of a wedge, another simple machine. A ramp is an inclined plane, again a single simple machine. A bicycle, however, clearly combines several elements: wheels and axles, levers in the form of pedals and brake levers, gears, and sometimes pulleys in the chain system. Therefore, a bicycle qualifies as a compound machine because it uses multiple simple machines at once.

Step-by-Step Solution:

Verification / Alternative check:

Textbooks on simple machines often show a bicycle as a classic example of a compound machine. They break it down into its components and label the wheels and axles, chain and gears, and lever systems. In contrast, examples of single simple machines include a hammer (lever), screwdriver (wheel and axle), knife (wedge), and ramp (inclined plane). This common treatment supports the conclusion that a bicycle is the only compound machine in the list.

Why Other Options Are Wrong:

• Screw: It is a single simple machine derived from an inclined plane and does not combine multiple simple machines.
• Knife: Functions mainly as a wedge and is therefore a simple machine.
• Ramp: An inclined plane on its own, again a simple machine rather than a compound one.

Common Pitfalls:

A learner may misinterpret compound machine as simply a complicated looking device. However, the definition depends on the presence of more than one type of simple machine. Another error is to think that because a screw or knife has more than one physical part, it must be compound. The correct criterion is the variety of simple machine principles involved, not the number of parts.

Final Answer:

A bicycle is a compound machine because it combines several simple machines.