A hand-crank winch is a simple machine that helps lift a load by winding string around a spool. Building one from cardboard, a pencil or dowel, and string lets students see how a wheel and axle works in a real device. This project connects classroom physics to cranes, elevators, fishing reels, and well buckets.
It is also a good way to practice careful measuring, safe cutting, and testing a design.
Key Facts
- A winch lifts by wrapping a rope or string around a rotating spool.
- Wheel and axle mechanical advantage = wheel radius / axle radius.
- Torque = force x radius, so a longer crank can create more turning effect.
- Work input is approximately equal to work output in an ideal machine: F_in d_in = F_out d_out.
- A larger spool lifts the load faster but usually needs more turning force.
- Friction in the axle and string reduces the real mechanical advantage.
Vocabulary
- Winch
- A winch is a device that winds a rope or string around a spool to pull or lift a load.
- Axle
- An axle is a rod that turns and supports a wheel, spool, or crank.
- Crank
- A crank is a handle attached to an axle that you turn to make the axle rotate.
- Mechanical advantage
- Mechanical advantage is the factor by which a machine changes the size of the input force.
- Torque
- Torque is the turning effect produced when a force acts at a distance from the axis of rotation.
Common Mistakes to Avoid
- Making the frame too weak, because thin or wobbly cardboard can bend and let the axle tilt instead of turning smoothly.
- Tying the string loosely to the spool, because the string may slip and fail to lift the bucket even when the crank turns.
- Putting the crank too close to the axle, because a short crank gives less torque and makes the load harder to lift.
- Using a load that is too heavy, because the string, tape, axle, or cardboard frame may break and make the test unsafe.
Practice Questions
- 1 A winch has a crank radius of 12 cm and a spool radius of 3 cm. What is the ideal mechanical advantage?
- 2 A student applies 4 N of force to a crank with a radius of 0.10 m. What torque does the student apply?
- 3 If two winches use the same crank but one has a larger spool, explain which winch lifts the bucket faster and which one is usually easier to turn.