How Machines Work

Shop / engineering: wheel and axle

Shop / engineering: wheel and axle

Wheel& axle.

One rigid piece. The handwheel and the shaft turn through the same angle. The radii are different, so the force is different.

R wheelR axle Ideal mechanical advantage when you drive the wheel. The load stays 10 lb. Drive the axle and the ratio flips.

Setting the wheel and axle on the bench…

Lesson Shop / engineering: wheel and axle

Left: turn the wheel, load on the axle. Right: turn the axle, load on the rim. Drag to look.

02 Bench Shop / engineering: wheel and axle

Change the radii.

The load stays 10 lb. Ideal mechanical advantage is the wheel radius divided by the axle radius. The axle stays smaller than the wheel.

What a wheel and axle is for

Force or reach

Drive the wheel. Your effort is on the rim. The load is on the axle. Winch, screwdriver, steering wheel, doorknob.

The wheel is the long radius, so you use less force. Your hand moves farther than the load. A 10 lb load needs less than 10 lb.

The wheel and the axle are one piece. They turn together. A longer rim means a bigger ideal advantage, and a longer path for your hand. This model leaves out friction.

Try this

Choose Winch. Cover the readout. 6 ÷ 1.5 = 4, so a 10 lb load on the axle needs 2.5 lb at the wheel. Uncover and check. Then read the other effort. The same 10 lb on the rim needs 40 lb at the axle.

04 Shop floor Ten minutes at the bench

Turn thelong radius.

Use this page next to a handwheel, a shaft, and a weight. The classroom use is the wheel and axle, and which radius you choose to turn.

04.1

Learning objectives

  • Point to the wheel and the axle on one rigid body.
  • Compute ideal mechanical advantage as R wheel / R axle.
  • Predict the effort for a 10 lb load when the wheel is driven.
  • State that driving the axle flips the ratio and raises the effort.

04.2

Classroom loop

  1. Cover the readout. Students divide the two radii on Winch before looking.
  2. Uncover 4.00 : 1. Ask for the effort that lifts 10 lb from the axle.
  3. Check 2.50 lb. Then ask what happens if the hand moves to the axle.
  4. Uncover 40.0 lb. Name a shop tool that turns the large radius, and one that turns the shaft.

04.3

Shop examples

Drive the wheel: winch, windlass, screwdriver, steering wheel, doorknob. Drive the axle: a fan, or a wheel powered at the hub. This model is ideal. It leaves out friction and the bend of a real shaft.