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Daily Read / Forces and simple machines

Forces and simple machines · Use a labelled diagram together with the text to explain that a screw's thread is a ramp wrapped around a rod, define pitch, and compare screws with different pitches to predict which needs a smaller push and which needs more turns

How Does a Screw Work? A Ramp Wrapped Around a Rod

A screw is a ramp wrapped around a rod. Use a labelled diagram to learn what pitch means and why a screw needs many turns but only a small push.

Suggested Grades 3–5594 core-passage words20 questions
A screwdriver turns a wood screw with clearly visible spiral threads into wood.
The threads of a screw form a spiral inclined plane; AI-generated illustration. Generation provenance
What you’ll practiseDescribe a screw as an inclined plane (ramp) wrapped around a rod, explain that one full turn moves the screw forward by one pitch, explain that the hand travels around a much longer circle than the screw advances so a small push becomes a large force, compare two screws with different pitches, and say why friction makes real results a little weaker than ideal ones.

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Find the hidden ramp

Hold a wood screw up to the light and trace the spiral edge with your finger. Your finger climbs a slope, goes around the rod, and climbs again. That spiral edge is called the thread. It looks nothing like the ramp from the last Daily Read lessons, but it is the same machine in disguise.

A U.S. Navy training manual called Basic Machines says that a screw is actually an inclined plane wrapped around a cylinder. A cylinder is a rod or a can shape with round ends. The manual suggests a test you can picture: wrap a paper triangle around a pencil, and its sloped edge winds up into a spiral thread.[1]

What is a screw?

EBSCO Research Starters, an online reference library, defines a screw as an inclined plane with a spiralling groove wrapped around a cylinder. It says screws use the inclined plane to redirect and increase a turning force. Turning force has a special name, torque. When you twist a screw, the turning becomes a straight-line movement along the rod.

That is why you twist a screwdriver around and around, and the screw moves straight into the wood. The twisting is the input. The forward movement is the output.[3]

Pitch: the gap between threads

The Navy manual defines pitch as the distance between identical points on the same thread. Look at the diagram: measure from the top of one turn of the thread to the top of the next turn. That gap is the pitch. EBSCO adds that a smaller pitch means the threads are packed more tightly.

The manual also explains what pitch does. When a screw makes one full turn, it raises its height by exactly one pitch. Screws with widely spaced threads move far in one turn. Screws with tightly packed threads move only a little in one turn, so they need more turns to go the same distance.[1]

How much stronger?

A physics textbook from LibreTexts looks at a jackscrew, a tall screw used to lift heavy loads such as one corner of a car. A long arm is fixed to the screw. When the arm makes one full turn, the load rises by one pitch. The hand, meanwhile, has gone all the way around a big circle. The textbook finds that, for an ideal jackscrew, the force is multiplied by the length of the circle the arm travels divided by the pitch.

Here is an invented example with easy numbers. A screwdriver handle travels about 60 millimetres around in one turn, and the screw has a pitch of 2 millimetres. Sixty divided by two is thirty, so in an ideal screw the push is multiplied about 30 times. The price is distance: your hand moves about 30 times as far as the screw does, which is why you turn it so many times.

No machine is perfect. EBSCO says that in the real world some force is always lost to friction, so real screws do less than the ideal number promises.[2]

Screws that lift water, hold wood and push air

According to legend, the Greek inventor Archimedes created the screw pump that bears his name. It uses a screw to lift water. EBSCO also lists clamping or crushing objects, drilling holes, and moving air in fans and propellers among the uses for screws.

The Navy manual points out a useful side effect of friction in a jack. Its threads are cut so that more force goes into overcoming friction than into doing useful work. Without that design, the load would turn the jack back down as soon as the handle was released. Friction here is a helper: it holds the car up while you rest.[3]

Explore the instructional diagram
A screw seen from the side beside an unrolled ramp. The slanted thread on the screw is a ramp wrapped around a rod. The distance between two neighbouring turns of the thread is called the pitch. One full turn of the screw moves it forward by one pitch, so the thread works like a long, gentle ramp whose rise is the pitch and whose long base is the distance once around the rod. Screw: a ramp wrapped around a rod Simplified schematic · side view · not to scale · the numbers are an invented example pitch (one turn apart) thread head Thread unrolled is a gentle ramp long base = once around rise = pitch In one full turn • The screw moves forward one pitch. • Your hand goes once around a circle,a much longer path than one pitch. Invented example: pitch 2 mm · screwdriver handle goesabout 60 mm around in one turn 60 mm ÷ 2 mm = about 30 times the push Where to find one • Wood screws, bolts, jar lids, light-bulb bases• A jackscrew lifts a car with a long lever arm The trade-off: finer threads (smaller pitch) mean a smaller push but more turns Friction makes real forces a little weaker · Ideal numbers ignore friction
Simplified schematic, not to scale. The thread is a ramp wrapped around a rod; one full turn moves the screw forward by one pitch while the hand travels once around a much longer circle. The 2 mm pitch and 60 mm hand path are an illustrative example, not a measurement; in an ideal screw with no friction the push is multiplied by about 30, but real screws lose some of that to friction.

Fast lesson

Use these checks before you answer the practice questions.

Use real objects

Let your child feel a screw, a bolt and a jar lid. Tracing the thread with a finger shows the slope better than any picture.

Pitch is a distance

Ask your child to point at the pitch on the diagram. It is the gap along the rod from one turn of the thread to the next, not the number of threads.

Keep ideal and real separate

The 30 in the article is an ideal, invented value. Encourage your child to say 'about' because friction always takes a little.

Link the simple machines

Ask: which machine is hidden in a screw (the ramp)? Which machine is the screwdriver handle and shaft (the wheel and axle)? Use because and so to explain.

Common mistakes

Thinking a screw with closer threads moves farther in one turn.

Why this fails: Close threads mean a small pitch, so each turn moves the screw only a little.

Thinking the thread is a separate part stuck on the rod.

Why this fails: The thread is the ramp wrapped around the rod; unwrap it in your mind and it is a long, gentle slope.

Thinking a screw makes the job need no effort.

Why this fails: The push is smaller, but it must be applied over many turns, and friction takes some of it.

Word Lab

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

screw

noun

a simple machine made of a ramp wrapped around a rod

The screw moved forward when she turned it.

thread

noun

the spiral ramp that winds around a screw

Trace the thread with your finger.

pitch

noun

the distance between one turn of a screw's thread and the next

A screw with a small pitch has tightly packed threads.

inclined plane

noun phrase

a sloping surface, or ramp, used to raise a load

A screw is an inclined plane wrapped around a rod.

cylinder

noun

a round shape like a rod or a can, with two flat circular ends

The thread winds around a cylinder.

torque

noun

a turning force

A screwdriver applies torque to the screw.

spiral

noun

a curve that winds around a centre again and again

The thread forms a spiral around the rod.

revolution

noun

one full turn around a centre

One revolution moves the screw forward by one pitch.

jackscrew

noun

a tall screw with a long arm, used to lift heavy loads

A jackscrew can lift one corner of a car.

circumference

noun

the distance once around a circle

The hand travels the circumference of a big circle.

friction

noun

a force that acts against motion when two surfaces rub together

Friction keeps the jack from turning back down.

redirect

verb

to send in a new direction

A screw redirects a turning force into a straight movement.

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 is the pitch of a screw?
Show answer and explanation

Answer: The distance between identical points on the same thread. The manual defines pitch as the distance between identical points on the same thread. The length of the screw and the width of the head are different measurements, and counting threads gives a number, not a distance.

Diagram and text2. The diagram shows the thread of a screw next to an unrolled triangle. What does the pairing show?
Show answer and explanation

Answer: The thread is a ramp wrapped around a rod.. The unrolled triangle is a ramp, and the thread is that ramp wrapped around the rod. A lever needs a fulcrum, a pulley needs a rope, and a screw clearly turns, so it has moving parts.

Compare3. Screw A has a pitch of 2 mm and Screw B has a pitch of 1 mm. The same screwdriver turns both, so the hand travels the same distance per turn. Which statement is true for ideal screws?
Show answer and explanation

Answer: Screw B multiplies the push about twice as much but needs twice as many turns for the same depth.. The hand path divided by 1 mm is twice the hand path divided by 2 mm, so Screw B gives twice the help, and it moves only 1 mm per turn so it needs twice the turns. Widely spaced threads give less help, the pitch matters as well as the screwdriver, and closer threads mean more turns, not fewer.

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 does the Navy manual say a screw actually is?

Locate

2. What is the spiral edge of a screw called?

Locate

3. What is the special name for a turning force?

Locate

4. When a screw makes one full turn, how far does it move forward?

Locate

5. What is a jackscrew used for?

Locate

6. Who is the screw pump said to be named after, according to legend?

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: A screw needs many turns, because …

Explain

8. Finish the sentence: The hand travels a long way around a circle, so …

Explain

9. Why does a screw with a smaller pitch give more help?

Explain

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

Explain

11. In the invented example, how much stronger is the ideal push? Show the division.

Own words

12. In one sentence, explain what pitch means and give one example of a screw with a small pitch.

Reason · Screws, ramps and trade-offs

Reason · Screws, ramps and trade-offs practice

Use what you learned to reason about new situations.

Classify

13. The spiral groove on a jar lid winds around a round neck. Is it a screw thread or not?

  1. Screw thread
  2. Not a screw thread
Classify

14. A straight, smooth nail with no spiral. Is it a screw thread or not?

  1. Screw thread
  2. Not a screw thread
Predict

15. Two screws are the same length, but Screw X has threads twice as close together as Screw Y. Predict the ideal effect on the push and on the number of turns to go in.

Compare

16. Why is a jackscrew arm made so long?

Connect

17. How is the thread of a screw like the ramp in the ramp lesson?

Practice answer key

  1. 1. An inclined plane wrapped around a cylinder.
    See 'Find the hidden ramp'.
  2. 2. The thread.
    See 'Find the hidden ramp'.
  3. 3. Torque.
    See 'What is a screw?'
  4. 4. One pitch.
    See 'Pitch: the gap between threads'.
  5. 5. Lifting heavy loads, such as one corner of a car.
    See 'How much stronger?'
  6. 6. Archimedes.
    See 'Screws that lift water, hold wood and push air'.
  7. 7. … each turn moves it forward by only one pitch.
    The distance per turn is the pitch.
  8. 8. … a small push is multiplied into a larger force on the screw.
    This is the force-for-distance trade.
  9. 9. Because the hand path divided by the pitch gets bigger, so the force is multiplied more, but more turns are needed.
    Ideal advantage = hand path ÷ pitch.
  10. 10. … the real force multiplication is a little less than the ideal number.
    EBSCO notes this.
  11. 11. About 30 times, because 60 mm ÷ 2 mm = 30.
    Use hand path ÷ pitch.
  12. 12. Pitch is the distance between one turn of the thread and the next; a jar lid has closely spaced threads.
    The jar lid is an everyday example; the definition is in the article.
  13. 13. Screw thread
    It is a ramp wrapped around a cylinder, so the lid is a screw.
  14. 14. Not a screw thread
    There is no ramp wrapped around the rod, so it works differently.
  15. 15. Screw X needs about half the push for each turn but about twice as many turns.
    Halving the pitch doubles the ratio and doubles the turns.
  16. 16. A long arm travels a longer circle compared with the pitch, so a small push can lift a heavy load.
    The ratio of arm path to pitch matters.
  17. 17. Both are inclined planes that raise a load by a long, gentle path, so less force is needed.
    The screw is the ramp wrapped around a rod.

Related skills

How Does a Wheel and Axle Work? Big Circle, Small CircleHow Does a Ramp Work? The Inclined Plane and the Longer PathHow Does a Pulley Work? Fixed, Movable and the Rope Trade-OffReading Library

Put it in your own words

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Check your own explanation

This is self-review, not automatic marking.

Compare with a model response

A screw is a simple machine made of a ramp, called the thread, wrapped around a rod. The distance from one turn of the thread to the next is the pitch. Because one full turn moves the screw forward by only one pitch, my hand travels around a much longer circle than the screw moves. As a result, a small push becomes a strong force, so a screwdriver can drive a screw into wood. However, the screw needs many turns, 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. A jar lid is an example of a screw with closely spaced threads.

Sources and revision notes

Source check: 2026-11-06. Grade guidance is an editorial suggestion, not a standardised reading score.

  1. U.S. Navy training manual Basic Machines, Chapter 5: The screw (reposted by Integrated Publishing)
  2. LibreTexts Physics — 25.05: Wedge and Screws (Prince George's Community College)
  3. EBSCO Research Starters — Simple Machines: Screw
What changed in this edition?

The statement that a screw is an inclined plane wrapped around a cylinder, the paper-triangle-around-a-pencil picture of a thread, the definition of pitch, the statement that one full turn raises the screw by one pitch, and the note that a jack's threads are cut so that friction holds the load come from the Navy manual. The jackscrew example and the rule that the force is multiplied by the length of the circle travelled by the arm divided by the pitch come from LibreTexts. The definition of a screw as an inclined plane with a spiralling groove, the description of torque being redirected and increased, the note that a smaller pitch means tighter threads, the Archimedes screw-pump legend, the other uses of screws, and the statement that some force is always lost to friction come from EBSCO. The 2-millimetre pitch and 60-millimetre hand path, the jar-lid example, the screw comparisons, the invented tests and the home activity are original illustrations or reasoning. Report errors through Sources and corrections.

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