Study CommonsRead · reason · practise

Daily Read / Forces and simple machines

Forces and simple machines · Explain how a wheel and axle lets a small turning force on a big wheel make a bigger force at the small axle, compare wheel and axle sizes, and tell a true wheel and axle from a wheel that simply spins on a fixed rod

How Does a Wheel and Axle Work? Big Circle, Small Circle

Doorknobs, screwdrivers and old well cranks are wheels and axles. Learn why turning the big circle is easier, and what it costs in distance.

Suggested Grades 3–5774 core-passage words20 questions
A child's hand turns a large round doorknob connected to a smaller spindle.
A doorknob uses a wheel-and-axle mechanism to turn a latch; AI-generated illustration. Generation provenance
What you’ll practiseDescribe a wheel and axle as a wheel or crank fixed to a rod so that both turn together, explain that turning the larger wheel lets a smaller force make a larger force at the axle, explain that the hand must travel farther around the big circle, and compare the radius of the wheel with the radius of the axle to predict how much the force is multiplied.

Device/browser voice. Pronunciation and availability vary.

Try the doorknob test

Find a round doorknob and grab the narrow metal rod right behind it, if you can reach it, or imagine doing so. Turning that thin rod with your fingertips is hard work. Now turn the big round knob. The latch slides open easily. The knob and the rod are joined, so they turn together, but one is much easier to turn.

A U.S. Navy training manual called Basic Machines uses the doorknob as its first example of a simple machine called a wheel and axle. In the Daily Read lessons on levers, pulleys and ramps, you met three other simple machines. This one is hiding in almost every house.[3]

What is a wheel and axle?

The Navy manual explains that a wheel-and-axle machine is a wheel or a crank rigidly attached to an axle, which turns with the wheel. Rigidly attached means fixed tightly, so the two parts cannot turn separately. A crank is a handle that you push around in a circle, like the handle on a pencil sharpener.

Energy Education, an online science encyclopedia from the University of Calgary, calls the wheel and axle a type of simple machine used to make tasks easier. It also points out that the wheel and the axle rotate at the same rate. When the wheel makes one full turn, the axle makes one full turn in exactly the same time.[2]

Same turn, different circles

If both parts make one turn, what is different? The size of the circle. Put a dot on the edge of the big wheel and another dot on the edge of the thin axle. In one turn, the dot on the wheel travels all the way around a big circle. The dot on the axle travels around a tiny circle. Your hand on the wheel moves a long way, while the axle's edge moves only a short way.

Energy Education says a wheel and axle changes the force by changing the distance over which the force must be applied. Your hand pushes gently over a long path around the big circle. The axle turns with a stronger force over its short path. You win on force and pay with distance, the same deal you met with levers, pulleys and ramps.[2]

How much stronger?

Britannica describes the wheel and axle as a basic machine part for amplifying force, which means making a force bigger. It explains that the mechanical advantage depends on the size of the large circle compared with the small one. Energy Education gives the rule for an ideal wheel and axle as the radius of the wheel divided by the radius of the axle. A radius is the distance from the centre of a circle to its edge.

Here is an invented example with easy numbers. A knob has a radius of 3 centimetres, and the rod behind it has a radius of 1 centimetre. Three divided by one is three, so in an ideal machine the rod turns with about three times the force your hand gives the knob. Make the knob bigger, or the rod thinner, and the force grows even more.

Real machines never quite reach the ideal number. Britannica notes that friction makes the actual mechanical advantage lower. Parts rub as they turn, so some of your push is used up.[1]

Buckets, screwdrivers and steering wheels

Britannica says that in its earliest form, the wheel and axle was probably used for raising weights or water buckets from wells. Picture a rope wound around a thick log over a well, with a crank handle on the end. As someone turns the crank in a big circle, the log turns too, and the rope winds up, lifting the bucket.

The Navy manual works through a well like this: a crank handle with a radius of 8 inches turns a drum with a radius of 2 inches, so the ideal mechanical advantage is 4. The same manual lists a screwdriver and a car's steering wheel as wheels and axles. A screwdriver's fat handle is the wheel, and the thin metal shaft is the axle.[1]

Not every wheel counts

Here is a surprise. The Navy manual says a car's front wheel is not a wheel-and-axle machine, because the axle does not turn with the wheel. The wheel spins freely around a rod that stays still. Nothing is fixed together, so there is no small circle being turned with extra force.

So when you meet a wheel, ask two questions. Are the wheel and the rod fixed together so they turn as one? If yes, which part does your hand turn? Turn the big circle, and you get more force with a longer path. That is why a skinny screwdriver handle feels so much harder to use than a fat one.[3]

Explore the instructional diagram
Front view of a wheel and axle. A large wheel with a radius of 3 centimetres is fixed to a small axle with a radius of 1 centimetre at the same centre, so both turn together. A thin red arrow runs a long way around the edge of the wheel to show the hand pushing gently over a long path; a thick blue arrow runs a short way around the axle to show a stronger force over a short path. Notes on the right say both parts make the same number of turns, the hand's path is about three times longer, and in an ideal machine the axle turns with about three times the force, because 3 centimetres divided by 1 centimetre is 3. Three examples are listed: a doorknob, a screwdriver and a well crank. A bottom band says friction makes the real force a little smaller and that a wheel spinning on a still rod, like a car's front wheel, is not a wheel and axle. Wheel and axle: one turn, two circles Simplified schematic · front view · arrow thickness shows more or less force, not measurements wheel radius 3 cm axle 1 cm hand: gentle push, long path axle: strong turn, short path In one full turn • Fixed together, so each makes 1 turn. • The hand travels about 3 times fartherthan the edge of the axle. • Ideal force at the axle:3 cm ÷ 1 cm = about 3 times the push Where to find one • Doorknob: knob = wheel, rod = axle• Screwdriver: handle = wheel, shaft = axle• Well crank: handle circle = wheel, drum = axle The trade-off: a bigger wheel means a smaller push but a longer path for the hand Friction makes real forces a little weaker · A wheel spinning on a still rod (a car's front wheel) is not a wheel and axle
Simplified schematic, not to scale. The wheel and the axle are fixed together, so they make the same number of turns. The 3 cm and 1 cm radii are an illustrative example: in an ideal machine with no friction the axle turns with about 3 times the push, while the hand travels about 3 times farther. Real forces are a little weaker because of friction.

Fast lesson

Use these checks before you answer the practice questions.

Fixed together is the test

Before calling something a wheel and axle, ask whether the wheel and the rod turn as one. A wheel spinning on a still rod (a cart or car wheel) does not count.

Use radius, not 'size'

Children often say 'bigger' loosely. Ask them to measure from the centre to the edge, so the ratio rule makes sense.

Keep ideal and real separate

The 3 and 4 in the article are ideal values. Encourage your child to say 'about' because friction always takes a little.

Link the simple machines

This is the fourth simple machine in a row. Ask your child to state the force-for-distance rule for the lever, pulley, ramp and wheel and axle in their own words.

Common mistakes

Thinking the knob turns more times than the rod.

Why this fails: They are fixed together, so they turn the same number of times; only the size of the circles differs.

Calling every wheel a wheel and axle.

Why this fails: If the rod stays still and the wheel spins around it, nothing is multiplied.

Thinking a bigger wheel saves distance too.

Why this fails: A bigger wheel means less force but a longer path for the hand.

Word Lab

Use the meaning, hear the word, then try it in your own sentence.

wheel and axle

noun phrase

a simple machine made of a wheel or crank fixed to a rod so that both turn together

A doorknob is a wheel and axle.

axle

noun

the rod in the centre that a wheel turns with or around

The thin axle behind the knob moves the latch.

crank

noun

a handle you push around in a circle to turn something

She turned the crank to lift the bucket.

radius

noun

the distance from the centre of a circle to its edge

The knob has a radius of 3 centimetres.

rigidly

adverb

in a stiff, fixed way that does not bend or move

The wheel is rigidly attached to the axle.

rotate

verb

to turn around a centre point

The wheel and the axle rotate at the same rate.

amplify

verb

to make something bigger or stronger

A wheel and axle can amplify a force.

mechanical advantage

noun phrase

how many times a machine multiplies the force you put in

A bigger wheel gives a bigger mechanical advantage.

windlass

noun

a machine with a crank and a turning drum that winds up a rope to lift things

An old well used a windlass to lift the bucket.

latch

noun

a small bar that holds a door closed

Turning the knob pulls the latch back.

friction

noun

a force that acts against motion when two surfaces rub together

Friction makes the real force a little smaller than the ideal one.

drum

noun

a round, turning cylinder that a rope winds around

The rope wound around the drum as the crank turned.

Check your understanding

Choose an answer, explain your choice, and then check. Hints and retries are welcome.

Vocabulary in context1. According to the Navy manual, what makes something a wheel-and-axle machine?
Show answer and explanation

Answer: A wheel or crank fixed to an axle so they turn together. The manual says the wheel or crank is rigidly attached to the axle, which turns with it. A wheel spinning freely on a still rod is exactly the car-wheel case the manual rules out, a rope over a grooved wheel is a pulley, and having a wheel is not enough.

Cause and effect2. Why is it easier to turn a doorknob than the thin rod behind it?
Show answer and explanation

Answer: Your hand on the big knob moves farther, so less force is needed.. A wheel and axle trades distance for force: your hand travels a long path around the big circle with a small force. The knob and rod turn the same number of times, the material is not the reason, and friction never disappears.

Compare3. Wheel A has a radius of 6 cm and Wheel B has a radius of 3 cm. Both are fixed to the same 1 cm axle. Which statement is true for ideal machines?
Show answer and explanation

Answer: Wheel A multiplies the force about 6 times; Wheel B about 3 times.. 6 ÷ 1 = 6 and 3 ÷ 1 = 3, so the bigger wheel multiplies the force more. A smaller wheel gives less help, the wheel size matters as well as the axle, and saying Wheel A gives about 3 times swaps the two results.

Try the questions here. Public practice does not save a learning record.

Support · Find it in the text

Support · Find it in the text practice

Each answer is stated in the article. Point to the sentence.

Locate

1. What everyday object does the Navy manual use as its first example of a wheel and axle?

Locate

2. What does rigidly attached mean?

Locate

3. According to Energy Education, how do the rates of the wheel and the axle compare?

Locate

4. What is a radius?

Locate

5. What does Britannica say the earliest wheels and axles were probably used for?

Locate

6. Why is a car's front wheel not a wheel-and-axle machine?

Apply · Cause and effect

Apply · Cause and effect practice

Use because or so to connect a cause with its effect.

Explain

7. Finish the sentence: Turning the big knob is easier than turning the thin rod, because …

Explain

8. Finish the sentence: The wheel and the axle are fixed together, so …

Explain

9. Why does a bigger wheel on the same axle give more help?

Explain

10. Finish the sentence: Friction is always present, so …

Explain

11. In the invented doorknob example, how much stronger is the force at the rod in an ideal machine? Show the division.

Own words

12. In one sentence, explain what a crank is and give one example.

Reason · Wheels, axles and trade-offs

Reason · Wheels, axles and trade-offs practice

Use what you learned to reason about new situations.

Classify

13. A pencil sharpener with a handle that you turn in a circle, fixed to the cutter inside. Wheel and axle or not?

  1. Wheel and axle
  2. Not a wheel and axle
Classify

14. A shopping-cart wheel that spins on a bolt that does not turn. Wheel and axle or not?

  1. Wheel and axle
  2. Not a wheel and axle
Predict

15. You swap a tap's small round handle for one twice as wide on the same stem. Predict the ideal effect on the force and on how far your hand moves.

Compare

16. Why is a steering wheel much bigger than the steering column it turns?

Connect

17. How is the well windlass like a pulley lesson's movable pulley?

Practice answer key

  1. 1. A doorknob.
    See 'Try the doorknob test'.
  2. 2. Fixed tightly, so the two parts cannot turn separately.
    See 'What is a wheel and axle?'
  3. 3. They rotate at the same rate.
    See 'What is a wheel and axle?'
  4. 4. The distance from the centre of a circle to its edge.
    See 'How much stronger?'
  5. 5. Raising weights or water buckets from wells.
    See 'Buckets, screwdrivers and steering wheels'.
  6. 6. Because the axle does not turn with the wheel.
    See 'Not every wheel counts'.
  7. 7. … my hand moves a longer distance around the big circle, so it needs less force.
    This is the force-for-distance trade.
  8. 8. … they always make the same number of turns.
    Rigidly attached parts turn as one.
  9. 9. Because the ratio of wheel radius to axle radius gets bigger, so the force is multiplied more.
    Ideal advantage = wheel radius ÷ axle radius.
  10. 10. … the real mechanical advantage is a little less than the ideal one.
    Britannica notes this.
  11. 11. About 3 times stronger, because 3 cm ÷ 1 cm = 3.
    Use the radius rule.
  12. 12. A crank is a handle you push around in a circle to turn something, like the handle on a pencil sharpener or a well.
    Both examples appear in the article.
  13. 13. Wheel and axle
    The crank is fixed to the part it turns, so they turn together.
  14. 14. Not a wheel and axle
    Like the car's front wheel, the wheel spins freely and the rod stays still.
  15. 15. The force needed is about halved, and your hand moves about twice as far for each turn.
    Doubling the wheel radius doubles the ratio.
  16. 16. A big wheel lets the driver turn the column with less force, at the cost of moving the hands farther.
    The Navy manual lists steering wheels as wheels and axles.
  17. 17. Both let a person lift a heavy bucket or load with less force by pulling or turning through a longer distance.
    Both trade force for distance.

Related skills

How Does a Ramp Work? The Inclined Plane and the Longer PathHow Does a Pulley Work? Fixed, Movable and the Rope Trade-OffHow Does a Lever Work? Fulcrum, Effort and LoadReading Library

Put it in your own words

This draft is not saved when you leave or refresh the page.

Check your own explanation

This is self-review, not automatic marking.

Compare with a model response

A wheel and axle is a simple machine made of a big wheel or crank fixed to a thin rod called an axle. Because they are fixed together, they always make the same number of turns. When I turn a doorknob, my hand travels around a big circle, but the rod behind it only turns a tiny circle. As a result, my small push becomes a bigger force at the rod. However, my hand has to move farther, so I am trading distance for force. Friction always uses up some of the push, so the real help is a little less than the ideal number. That is why a screwdriver with a fat handle is easier to use than a skinny one.

Sources and revision notes

Source check: 2026-11-05. Grade guidance is an editorial suggestion, not a standardised reading score.

  1. Britannica — wheel and axle
  2. Energy Education (University of Calgary) — Wheel and axle
  3. U.S. Navy training manual Basic Machines, Chapter 3: The wheel and axle (reposted by Integrated Publishing)
What changed in this edition?

The description of the wheel and axle as a basic machine component for amplifying force, the statement that its earliest form was probably used for raising weights or water buckets from wells, the rule that mechanical advantage depends on the large radius compared with the small radius, and the note that friction makes the actual mechanical advantage lower come from Britannica. The description as a simple machine used to make tasks easier, the statement that the wheel and axle rotate at the same rate, the statement that it changes force by changing the distance over which force is applied, and the ideal mechanical advantage of wheel radius divided by axle radius come from Energy Education. The definition of a wheel or crank rigidly attached to an axle that turns with it, the doorknob, screwdriver and steering-wheel examples, the well crank with an 8-inch handle radius and a 2-inch drum radius giving a theoretical mechanical advantage of 4, and the statement that a car's front wheel is not a wheel-and-axle machine because the axle does not turn with the wheel come from the Navy manual. The doorknob test, the two-dot comparison, the 3-centimetre knob example, the pencil-sharpener crank, the skinny-screwdriver comparison, the invented force test and the home activity are original illustrations or reasoning. Report errors through Sources and corrections.

Choose another reading