Grade by Grade
D. Structures and Mechanisms · Machines and Mechanisms

Four Kinds of Motion and How Mechanisms Pass Them Along

D2.3 A1.5About 35 minutes
Learning goals
  • I can name and describe four kinds of motion: linear, rotary, reciprocating and oscillating.
  • I can give examples of each kind of motion.
  • I can describe how mechanisms like axles, gears, chains and belts transmit (pass along) rotary motion from one part to another.

Words to know

linear motion
Moving in a straight line in one direction, like a sled sliding down a straight hill.
rotary motion
Turning round and round in a circle, like a wheel or a fan.
reciprocating motion
Moving back and forth in a straight line, like a saw cutting wood.
oscillating motion
Swinging back and forth along a curved path, like a playground swing.
transmit
To pass something along from one part to another.
shaft
A long rod that turns and carries rotary motion, like a long axle.

Remember from Grade 2

In Grade 2 you described how things move: in a straight line, in a curve, in a zigzag, round and round, and back and forth. Scientists and engineers have special names for the kinds of motion in machines. Let's learn them!

Four kinds of motion

  1. Linear motion: moving in a straight line, one way. A toboggan sliding down a straight hill. A train on a straight track. A zipper being pulled up.
  2. Rotary motion: turning round and round in a circle. A wheel. A ceiling fan. A drill bit.
  3. Reciprocating motion: moving back and forth in a straight line. A saw cutting wood. A sewing machine needle going up and down. The handle of a bicycle pump pushing in and out.
  4. Oscillating motion: swinging back and forth along a curved path. A playground swing. The pendulum of a clock. Windshield wipers.
Empty swings hanging on chains from a metal frame in a park beside a lake.
A playground swing shows oscillating motion: it swings back and forth along a curved path. Can you spot something in the picture that would show rotary motion if it moved? AI-generated image
linearrotaryreciprocatingoscillating
The four kinds of motion: linear (straight line), rotary (round and round), reciprocating (back and forth in a straight line) and oscillating (swinging back and forth on a curve).

Reciprocating or oscillating?

Both go back and forth. Ask: is the path straight or curved?

  • Straight back and forth = reciprocating (a saw).
  • Curved, swinging back and forth = oscillating (a swing).

Passing motion along: transmitting

Most machines need to transmit (pass along) motion from one part to another, or from one system to another. Rotary motion is the kind most often passed along. Mechanisms that transmit rotary motion include:

  • Axles and shafts: a turning rod carries the turning to whatever is joined to it. A car's engine turns shafts that carry the turning to the wheels.
  • Gears: the teeth of one turning gear push the teeth of the next gear and make it turn.
  • Chains and sprockets: a chain carries the turning from one toothed wheel to another, like on a bike.
  • Belts and pulleys: a belt carries the turning from one pulley wheel to another, like in some sewing machines and car engines.
axle / shaftturning rodgearsteeth push teethchain + sprocketslike a bikebelt + pulleyssmooth belt
Four ways to transmit (pass along) rotary motion from one part to another: a turning shaft, meshing gears, a chain on sprockets, and a belt on pulleys.
ExampleKind of motion
a ceiling fan's bladesrotary
a toboggan on a straight hilllinear
a saw cutting a boardreciprocating
a clock pendulumoscillating
a merry-go-roundrotary
a sewing machine needlereciprocating
a car's windshield wipersoscillating
an elevator going straight uplinear
Sorting motions
Worked example

Let's follow the motion through a bicycle

Name the kind of motion at each step when you ride a bike on a straight road.

  1. Your feet push the pedals around. The pedals and crank arms turn in a circle: rotary motion.
  2. The chainring turns: rotary.
  3. The chain carries the motion from the chainring to the sprocket: it transmits the rotary motion.
  4. The sprocket and the back wheel turn: rotary.
  5. The whole bike moves along the straight road: linear motion!

The rotary motion is transmitted by the chain from the pedals to the back wheel. Then the turning wheel moves the bike in a straight line (linear motion).

Worked example

Let's follow the motion through a hand egg beater

What kind of motion goes in, and how is it passed along?

  1. You turn the crank: rotary motion goes in.
  2. The crank turns a big gear. Its teeth push the teeth of the small gears: the gears transmit the rotary motion.
  3. The small gears turn the beaters: rotary motion comes out.

Rotary in, rotary out. The gears transmit the rotary motion from the crank to the beaters.

Hands-on activity

Motion scavenger hunt and poster

You need: paper, coloured pencils, and things around your home.

  1. Fold a paper into 4 boxes. Label them linear, rotary, reciprocating and oscillating.
  2. Hunt for at least 2 examples of each kind of motion at home or outside. Ideas: a door on its hinges, a drawer, a toy car, a fan, a swing, a rocking chair, a salad spinner, a toothbrush, a wind-up toy.
  3. Draw each one in the right box. Add an arrow to show how it moves.
  4. Choose one machine that transmits rotary motion (like a salad spinner or a bike). Show your grown-up the part where the motion is passed along.
  5. Use your poster to teach someone in your family the four motion words.

What to look for: a straight arrow for linear, a circle arrow for rotary, a straight double arrow for reciprocating, and a curved double arrow for oscillating. A door on hinges swings on a curve. A drawer slides in and out in a straight line (reciprocating if you move it back and forth).

Just for fun

Riddle: A happy dog's tail swings back and forth along a curve. What kind of motion is that?

Oscillating! (Some dogs could power a fan with it.)

Your turn

1

What kind of motion is a spinning wheel?

2

A saw moves back and forth in a straight line. What kind of motion is that?

3

A swing moves back and forth along a curve. What kind of motion is that?

4

A sled slides straight down a hill. What kind of motion is that?

5

What does transmit mean?

6

Name two mechanisms that transmit rotary motion.

7

What transmits the motion from the pedals to the back wheel of a bike?

More practice: warm-up

1

What kind of motion is a ceiling fan?

2

What kind of motion is a clock pendulum?

3

What kind of motion is a sewing machine needle?

4

What kind of motion is an elevator going up?

5

Which kind of motion goes round and round?

More practice: on your own

1

How are reciprocating and oscillating motion alike? How are they different?

2

A rocking chair rocks back and forth. Which kind of motion is it? Explain.

3

In a salad spinner, you turn a handle on top and the basket inside spins. What kind of motion goes in and what comes out?

4

A drawer slides out in a straight line. Then you push it back in. What kind of motion is out-and-back-in?

5

Why do you think so many machines use rotary motion?

Challenge

1

A car's engine makes a shaft turn. The car moves forward along a straight road. Describe the kinds of motion and how the motion is transmitted.

2

A playground has a swing, a slide, a merry-go-round and a seesaw. Name the motion of each.

3

Design a machine that uses at least two kinds of motion. Draw it and label each kind.

Check your understanding

Quiz

1.

Turning round and round is called...

2.

A saw moving back and forth in a straight line shows...

3.

A playground swing shows...

4.

Which shows linear motion?

5.

On a bicycle, which part transmits the motion from the chainring to the back wheel's sprocket?

6.

To transmit motion means to...

For parents and teachers

Big idea (D2.3): Machines use four kinds of motion (linear, rotary, reciprocating, oscillating), and mechanisms such as axles, gears, chains and belts transmit (pass along) rotary motion from one part or system to another. Making a poster to teach the words is communication (A1.5).

How to help: Play "Name that motion" on walks and in the kitchen: a swinging door, a spinning washing machine, a sliding drawer.

Common difficulties:

  • Mixing up reciprocating and oscillating. Straight path = reciprocating; curved swing = oscillating.
  • Thinking a whole machine has only one kind of motion. Many machines have several (the bike's wheels turn while the bike moves in a line).
  • Long words. It is fine to say "round and round (rotary)" while the words become familiar.