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

Machines All Around Us

D2.1 A1.1 A1.5About 35 minutes
Learning goals
  • I can explain what a machine is and what a mechanism is.
  • I can name machines I use in daily life and describe the purpose (job) of each one.
  • I can tell a simple machine from a complex machine.
  • I can sort machines by their purpose and by what makes them go.

Words to know

machine
A device that helps us do work, like moving, lifting, cutting or turning something, by changing a force or a motion.
mechanism
The group of moving parts inside a machine that work together to do its job.
purpose
The job something is made to do.
simple machine
One of the six basic machines: lever, wheel and axle, pulley, inclined plane, wedge and screw.
complex machine
A machine made of two or more simple machines or mechanisms working together, like a bicycle. It is also called a compound machine.
energy source
What makes a machine go: a person's muscles, electricity, fuel such as gas, or wind and water.

Remember from Grade 2

In Grade 2 you met the six simple machines: the lever, the wheel and axle, the pulley, the inclined plane, the wedge and the screw. You learned that machines make work easier, and that a compound machine uses two or more simple machines together.

In Grade 4 you will look inside machines. You will find out how their moving parts pass motion along, change the kind of motion, change speed and direction, and change forces. You will also study two very important mechanisms: pulleys and gears.

A morning full of machines

It is a snowy January morning. Before school, Amira:

  • opens a can of soup for her lunch with a can opener
  • rides an elevator down from her apartment
  • watches a snowplow clear the street
  • rides her bicycle... no, wait, there is too much snow! She takes the bus.

That is four machines before 9 o'clock (the can opener, the elevator, the snowplow and the bus)! Machines are everywhere. Each one has a purpose, a job it was made to do.

An orange snowplow with a wide blade pushes deep snow off a residential street on a snowy day.
A snowplow is a big machine with one purpose: moving snow off the road. Its blade changes the direction the snow goes, pushing it to the side of the street. AI-generated image

What is a machine?

A machine is a device that helps us do work. Work means using a force to move something, like lifting, pushing, turning, cutting or carrying.

A machine helps by changing a force (how hard you push or pull) or a motion (how something moves).

Inside most machines is a mechanism: a group of moving parts that work together. You put in a push, a pull or a turn. The mechanism changes it. Out comes the motion or force that does the job.

mechanism(moving parts)input:your forceoutput:motion or forcee.g. turna handlee.g. the lidcomes off
Input, mechanism, output. You turn the handle of a can opener (input). The gears and cutting wheel inside (the mechanism) cut the lid (output).

Simple machines and complex machines

  • A simple machine has very few parts, like a ramp or a lever. It does one simple thing.
  • A complex machine (also called a compound machine) is made of two or more simple machines or mechanisms working together. A bicycle is a complex machine. It has wheels and axles, gears, a chain, and levers for the brakes.

Most machines in your home are complex machines.

MachinePurpose (its job)What makes it go
hand can openercuts the lid off a cana person turns a handle
bicyclecarries a person from place to placea person pushes the pedals
snowplowpushes snow off roadsfuel (diesel)
elevatorlifts people and things between floorselectricity
hand egg beatermixes eggs or battera person turns a crank
staplerfastens papers togethera person presses down
washing machinecleans clotheselectricity
wheelbarrowcarries heavy loads, like soila person lifts and pushes
Machines in daily life and their purposes

Purpose words

Describe a machine's purpose with an action word: it lifts, moves, carries, cuts, mixes, fastens, opens, turns or cleans. "A stapler fastens papers together" is a clear purpose.

Worked example

Let's describe a machine's purpose

What is the purpose of a wheelbarrow, and is it a simple or complex machine?

  1. Ask: what job does it do? A wheelbarrow carries heavy loads like soil, snow or firewood.
  2. Look for parts that move: the wheel turns on an axle. The long handles lift the load like a lever, with the wheel as the fulcrum.
  3. It has two simple machines working together, so it is a complex machine.
  4. Ask what makes it go: a person lifts the handles and pushes.

A wheelbarrow's purpose is to carry heavy loads. It is a complex machine (a lever plus a wheel and axle) powered by a person.

loadeffort:lift herewheel and axle = fulcrumsoil in the trayhandle = lever
A wheelbarrow is a complex machine. The handles are a lever that turns on the wheel and axle, which is the fulcrum. A small lift at the handles raises the heavy load in the middle.
Worked example

Let's sort machines by energy source

Sort these machines: scissors, a hair dryer, a scooter, a lawn mower with a gas engine, a pencil sharpener you turn by hand, a fridge.

  1. Which ones use a person's muscles? Scissors, the scooter and the hand pencil sharpener.
  2. Which ones use electricity? The hair dryer and the fridge.
  3. Which one uses fuel? The gas lawn mower.

Muscles: scissors, scooter, hand pencil sharpener. Electricity: hair dryer, fridge. Fuel: gas lawn mower.

Just for fun

Why does the can opener get invited to every party?

It really knows how to open up!

Hands-on activity

Machine hunt and chart

You need: paper, a pencil and a ruler.

  1. Walk through your home with a grown-up. Find 10 machines. Look in the kitchen, the garage, the bathroom and your toy box. (Look only. Do not touch anything sharp, hot or plugged in.)
  2. Make a chart with 4 columns: Machine, Purpose, Simple or complex?, What makes it go?
  3. Fill in a row for each machine. Use an action word for each purpose.
  4. Circle the machine you think is the most useful. Tell your grown-up why.

What to look for: each purpose uses an action word ("it lifts", "it cuts"), and most home machines are complex machines. This is how scientists do research: they observe, record and organize what they find.

Your turn

1

What is a machine?

2

What is a mechanism?

3

What is the purpose of a hand can opener?

4

Is a ramp a simple machine or a complex machine?

5

Why is a bicycle a complex machine?

6

Name two machines that use electricity.

7

Finish the sentence with a purpose: "A snowplow ..."

More practice: warm-up

1

Name the six simple machines.

2

What is the purpose of a stapler?

3

What makes a scooter go?

4

What is another name for a complex machine?

5

True or false: most machines in your home are complex machines.

More practice: on your own

1

Describe the purpose of an elevator and what makes it go.

2

A hand egg beater and an electric mixer have the same purpose. What is it? How are they different?

3

Ken says, "A wedge is a complex machine." Is he right? Explain.

4

Sort into simple and complex: a doorstop, a bicycle, a ramp, a can opener.

5

Why is it useful to sort machines by purpose?

Challenge

1

Think of three different machines that all have the purpose "clear snow". Order them from the one that needs the most muscle power to the one that needs the least.

2

A pair of scissors has two levers joined at a pivot, and two blades that are wedges. Is it a simple or a complex machine? Explain.

3

Invent a new machine to help with a job at your home. Describe its purpose, one part that moves, and what makes it go.

Check your understanding

Quiz

1.

A machine helps us do work by changing...

2.

The moving parts inside a machine that work together are called...

3.

Which is a simple machine?

4.

What is the purpose of a hand can opener?

5.

Which machine is powered by a person's muscles?

6.

A wheelbarrow is a complex machine because...

For parents and teachers

Big idea (D2.1): Machines are everywhere, and each one has a purpose. Grade 4 builds on Grade 2's six simple machines by looking at mechanisms, the moving parts inside machines. Making and organizing a chart of machines practises research and communication skills (A1.1, A1.5).

How to help: During daily routines, ask "What machine is that? What is its job? What makes it go?" Encourage action words for purposes (lifts, cuts, mixes).

Common difficulties:

  • Thinking only things with motors are machines. A pair of scissors or a ramp is a machine too.
  • Describing what a machine looks like instead of its purpose. Ask "What job does it do?"
  • Safety: the machine hunt is for looking, not touching. Keep children away from sharp blades, hot appliances and anything plugged in.