D. Structures and Mechanisms · Machines and Mechanisms

Comparing Machines: Effects on the Environment

D1.2 A1.1 A3.2About 40 minutes

Learning goals

I can compare the environmental impacts of different machines that do the same job.
I can use criteria like energy source, air pollution, noise and how long a machine lasts.
I can use a scoring chart (a math tool) to compare machines fairly.
I can suggest ways to reduce the environmental impact of machines.

Words to know

environment
The natural world around us: air, water, land, plants and animals.

environmental impact
The effect something has on the environment.

criteria
The rules or things you check when you compare or judge something.

fuel
Something that is burned to make energy, like gasoline or diesel.

emissions
Gases and tiny particles that come out of a machine when it burns fuel. Some of them pollute the air.

e-waste
Old electrical and electronic machines and batteries that are thrown away. They should be recycled at special drop-off sites.

Three ways to cut the grass

The Patel family needs a new lawn mower. At the store they see three kinds:

a push reel mower (spinning blades turned by the wheels as you push; no motor)
an electric mower (runs on a battery or a cord)
a gas mower (has an engine that burns gasoline)

All three have the same purpose: cutting grass. But they have different environmental impacts. How can the Patels compare them fairly?

A push reel lawn mower with spinning blades between two wheels on a half-cut green lawn. — A push reel mower has no motor: turning the wheels spins the blades. It runs on muscle power, so it makes no emissions and little noise, but cutting takes more effort. AI-generated image

Criteria for comparing machines

To compare fairly, scientists use the same criteria for every machine:

Energy source: muscles, electricity or fuel?
Air pollution: does it make emissions where it is used?
Noise: loud machines can bother people and animals.
Materials: how much metal, plastic and other material does it take to build?
How long it lasts: can it be repaired, or is it thrown away?
End of life: can it be recycled? Batteries and electric parts are e-waste and must go to special drop-off sites.

Electric is not zero impact

An electric machine makes no exhaust where you use it. But the electricity has to be made somewhere. In Ontario, much of our electricity comes from nuclear power stations and from moving water (hydroelectricity), which make very little air pollution. Some also comes from natural gas power plants (which do make emissions) and from wind and sun. Every power station still affects the land or water around it. Batteries also take materials from mines and must be recycled.

Worked example

Let's compare three lawn mowers

Use a scoring chart. Give each mower 3 points (best), 2 points or 1 point (worst) for each criterion. Add the points.

Energy source: push reel uses muscles (3); electric uses electricity (2); gas burns gasoline (1).
Air pollution where it is used: push reel (3), electric (3, no exhaust), gas (1, makes emissions).
Noise: push reel is very quiet (3); electric is fairly quiet (2); gas is loud (1).
End of life: push reel is mostly metal and easy to repair (3); gas mower has an engine that can be repaired (2); electric mower's battery is e-waste and must be recycled (2).
Totals: push reel 3 + 3 + 3 + 3 = 12; electric 2 + 3 + 2 + 2 = 9; gas 1 + 1 + 1 + 2 = 5.

The push reel mower has the smallest environmental impact. But it takes more effort and works best on small lawns, so the family must also think about their needs.

Criterion	Push reel	Electric	Gas
energy source	3	2	1
air pollution where used	3	3	1
noise	3	2	1
end of life	3	2	2
Total	12	9	5

Scoring chart for three lawn mowers (3 = best for the environment)

The scoring chart as a stacked bar graph. Each colour is one criterion. The push reel mower (12 points) has the smallest impact on the environment; the gas mower (5 points) has the biggest.

Worked example

Let's compare ways to clear snow

Compare a snow shovel, an electric snowblower and a gas snowblower for clearing a driveway.

Shovel: muscle power; no emissions; silent; lasts many years. But it is hard work and slow for big driveways.
Electric snowblower: electricity; no exhaust where used; quieter than gas; battery or cord. Good for light and medium snow.
Gas snowblower: burns gasoline; makes emissions and is loud; very strong for deep, heavy snow and big driveways.
Environmental ranking (smallest impact first): shovel, electric snowblower, gas snowblower.

The shovel has the smallest environmental impact. People also think about their needs: someone with a long driveway or who can't shovel safely might need a snowblower.

The three snow-clearing machines placed on an impact line, from the smallest environmental impact (left) to the biggest (right).

Ways to reduce a machine's impact

Choose a muscle-powered machine when it can do the job (a bike for a short trip, a rake instead of a leaf blower).
Share machines (a neighbourhood tool library, a bus instead of many cars).
Keep machines repaired and use them carefully so they last longer.
Recycle batteries and electronics at proper drop-off sites.
Turn machines off when you aren't using them.

Just for fun

Funny but true: a push reel mower and a snow shovel both run on the same fuel... your breakfast! Muscle power comes from the energy in the food you eat.

Hands-on activity

Machine showdown

You need: paper, a pencil and a ruler.

Choose a job and two or three machines that do it. Ideas:

mixing batter: hand whisk, hand egg beater, electric mixer
getting to school: walking, bike, school bus, car
clearing leaves: rake, electric leaf blower, gas leaf blower
drying clothes: clothesline, electric dryer

Choose 4 criteria from the list in this lesson.
Make a scoring chart. Give 3, 2 or 1 points for each machine on each criterion. Ask a grown-up to help you research any you aren't sure about.
Add up the totals. Which machine has the smallest impact?
Write one sentence about needs: when might someone still choose the other machine?

What to look for: the same criteria used for every machine, correct addition, a ranking, and a sentence that thinks about people's needs too. Example: clothesline (muscles and sun, no emissions, silent) usually beats the dryer for the environment, but a dryer is useful on rainy days or in winter.

Your turn

What are criteria?

Name three criteria for comparing the environmental impact of machines.

Which usually has the smaller environmental impact: a rake or a gas leaf blower? Why?

Why isn't an electric machine "zero impact"?

What should you do with an old battery?

In a scoring chart, a push reel mower scored 12, an electric 9 and a gas 5. Which has the smallest impact?

More practice: warm-up

What is the purpose of all lawn mowers?

What are emissions?

Which is louder: a gas mower or a push reel mower?

What is e-waste?

Name one way to reduce a machine's impact.

More practice: on your own

Score a bike and a car for getting to a park 2 km away using energy source, air pollution and noise (3 = best, 1 = worst). Which wins?

Why should you use the same criteria for every machine you compare?

A hand egg beater and an electric mixer both mix batter. Compare their environmental impacts.

A family has a very long driveway and lots of heavy snow. Is it fair to say they are wrong to use a snowblower? Explain.

How is a scoring chart like a math tool?

Challenge

Create a scoring chart to compare a clothesline and an electric clothes dryer using 4 criteria. Show your totals.

A company says its new gas leaf blower is "better for the environment" than its old one because it uses less fuel. Is it better than a rake? Explain.

Suggest a plan for your school to reduce the environmental impacts of the machines its families use to get to school.

Check your understanding

Quiz

To compare machines fairly, you should...

Which machine makes emissions where it is used?

Which has the smallest environmental impact for clearing a small walkway?

Where should old batteries go?

An electric machine...

A scoring chart gives a bike 9 points and a car 4 points (higher = better for the environment). Which is better for the environment?

For parents and teachers

Big idea (D1.2): Different machines can do the same job with very different environmental impacts. Using consistent criteria and a scoring chart is research and analysis (A1.1) and connects science with math (A3.2).

Balance: Encourage your child to consider people's needs too. A snowblower may be the right choice for someone who can't shovel safely. The goal is thoughtful choices, not guilt.

Accuracy note: Exact environmental numbers vary by model and how a machine is used, so this lesson compares in general terms. If your child wants to research a specific product, look at the manufacturer's information together.

Common difficulties:

Thinking electric means zero impact. Talk about where electricity and batteries come from.
Using different criteria for different machines. Keep the same columns for each.
Adding scores. Check the addition together.