Questions: Combining Simple Machines

Question 1

Which simple machines are combined in a pair of scissors?

• A. A pulley and a wheel
• B. Two levers and two wedges
• C. A gear and an inclined plane
• D. A screw and a pulley

Answer: (B)

Scissors are two first-class levers joined at a fulcrum (the central screw or pin), and the blades are wedge-shaped — they taper to a thin cutting edge. When you squeeze the handles (lever action), the wedge-shaped blades concentrate force along a thin line to cut material.

Question 2

In a compound machine, combining simple machines eliminates the trade-off between force and distance.

• T. True
• F. False

Answer: False

Each simple machine in a compound machine still obeys the force-distance trade-off. Combining machines chains these trade-offs together. A bicycle, for example, uses gears to trade pedaling speed for wheel speed, and uses the wheel and axle to convert rotation into forward motion — but you still cannot get both more force and more speed for free.

Question 3

Choose an everyday compound machine and identify at least two simple machines inside it.

Model answer: A wheelbarrow contains a lever (the handles and tray pivot around the wheel) and a wheel and axle (the wheel at the front). The lever lets you lift a heavy load with less force by placing it close to the wheel, and the wheel reduces friction so you can roll the load instead of dragging it.

Many everyday objects are compound machines. Other examples: a can opener (lever + gear + wedge), a bicycle (wheel and axle + gears + lever), a hand drill (wheel and axle + screw + gear). Identifying the simple machines inside compound machines develops the analytical skill engineers use when designing new machines.