Grade by Grade
C. Matter and Energy · Properties of Liquids and Solids

How Melting and Freezing Affect People and Nature

C1.2 C2.3 A1.2 A3.1 A3.3About 40 minutes
Learning goals
  • I can describe ways melting and freezing help people.
  • I can describe problems that melting and freezing can cause, and ways people solve them.
  • I can describe how melting and freezing affect plants, animals and the land.
  • I can explain how some First Nations and Inuit communities depend on ice.

Words to know

impact
The effect something has. An impact can be helpful or harmful.
environment
Everything around a living thing: land, water, air, plants and animals.
freezing rain
Rain that freezes when it lands, covering everything in a coat of ice.
flood
When water covers land that is usually dry.
winter road
A road built over frozen lakes and land in winter. It can only be used when the ice is thick enough.
sea ice
Frozen ocean water. In the Arctic, it covers much of the ocean in winter.

Changes all around us

In Canada, we see melting and freezing all year. Snow falls and melts. Lakes freeze and thaw. Icicles grow and drip.

These changes of state have an impact on people, animals and the land. Some impacts are helpful. Some cause problems. Let's look at both.

Ways freezing and melting help people

  • Fun in winter: Frozen ponds and outdoor rinks are great for skating and hockey. In Ottawa, the frozen Rideau Canal becomes a long skating path when the ice is thick enough.
  • Keeping food fresh: Freezers keep food frozen so it lasts longer. Ice keeps drinks cold in a cooler.
  • Treats: We freeze juice to make popsicles and melt chocolate to dip strawberries.
  • Drinking water: In spring, melting snow fills rivers and lakes.

Ice roads and sea ice

In northern Ontario, some First Nations communities have no year-round road. In winter, when lakes and swamps freeze thick, people build winter roads over the ice and frozen land. Trucks use them to bring in food, fuel and building supplies. When spring comes and the ice melts, the winter road closes.

In the Arctic, Inuit have travelled, hunted and fished on sea ice for a very long time. Inuit hunters and Elders have deep knowledge about ice: how to tell when it is thick and safe, and when it is thin and dangerous. This knowledge is passed down from one generation to the next.

In many places, winters have been getting warmer. When the ice freezes later and melts sooner, winter roads can be open for fewer weeks, and travelling on sea ice can be harder and less safe.

Problems melting and freezing can cause

  • Icy sidewalks and roads: People can slip and fall, and cars can slide.
  • Freezing rain: It coats trees and power lines with heavy ice. Branches can break, and the power can go out.
  • Frozen pipes: Water takes up more space when it freezes. Water freezing inside a pipe can make the pipe burst.
  • Potholes: Water gets into cracks in the road. It freezes and pushes the cracks wider. After many freezes and melts, a hole forms.
  • Spring floods: When lots of snow melts quickly, rivers can rise and flood land, roads and basements.
  • Melting food: Ice cream and frozen food spoil if they melt and stay warm.
Tree branches coated in clear ice with icicles hanging from them after freezing rain, and a birch tree bent over in a snowy yard.
After freezing rain, ice coats every branch. The heavy ice can bend trees, like the birch in the back, and break branches. AI-generated image
1. Rain gets intoa crack in the road.ice2. The water freezesand pushes the crack wider.3. The ice melts.The crack is bigger.4. After many freezesand melts: a pothole!a road cut in half, seen from the side
How a pothole forms. Water takes up more space when it freezes, so each freeze pushes the crack a little wider.

Impacts on nature

  • Fish under the ice: Ice floats, so lakes freeze on top. Fish and frogs spend the winter in the liquid water underneath.
  • Animals on the ice: Polar bears hunt seals from the sea ice. When sea ice melts earlier, it is harder for them to find food.
  • Road salt: People spread salt to melt ice on roads and sidewalks. When the snow melts, salty water runs into streams and soil. Too much salt can hurt plants, fish and other animals that live in the water.
ice (solid water floats on top)skaterliquid water underneath: fish stay here all winterlake
Because ice floats, a lake freezes from the top down. The ice makes a skating surface, and fish keep swimming in the liquid water below.
Change of stateHelpful impactProblemOne way people help
water freezesskating rinks, winter roadsicy sidewalks, burst pipesspread sand; keep pipes warm
ice and snow meltwater for rivers and lakesspring floods, potholesclear drains; fix roads
freezing rain(very little)broken branches, power outtrim trees near power lines
Impacts of melting and freezing
Worked example

Let's solve a problem: the icy driveway

Overnight, freezing rain turned Noor's driveway into a sheet of ice. Her grandpa needs to walk to his car. What could the family do? Which choice is kindest to the environment?

  1. What is the problem? Ice is slippery, and someone could fall.
  2. Ideas: Spread sand for grip. Spread a small amount of salt to melt the ice. Wear boots with good grips or ice cleats. Hold the railing and walk slowly.
  3. Think about the environment: Salt melts ice, but too much salt can hurt plants and fish when it washes away. Sand gives grip without salt.
  4. Choose: Use sand, wear grippy boots, and use only a little salt where it is really needed.

Spread sand, wear grippy boots and use only a little salt. This keeps Grandpa safe and protects plants and streams.

Silly but true

A pothole is just a crack that went to the gym all winter: freeze, melt, freeze, melt... until it got really big!

Worked example

Let's explain: Why did the pipe burst?

During a very cold week in February, a water pipe in a family's unheated garage burst. Explain why.

  1. The garage was very cold, below 0°C.
  2. The water inside the pipe froze into ice.
  3. Water takes up more space when it freezes. The ice pushed outward on the pipe.
  4. The pipe could not stretch, so it cracked. When the ice melted, water leaked out.

The water froze and took up more space, so it pushed on the pipe until it burst. People wrap pipes or keep them warm to stop this.

Hands-on activity

Salt and ice test, and a melting-and-freezing chart

Part 1: Salt test (a grown-up helps)

You need: 2 ice cubes from the same tray, 2 plates, a pinch of salt.

  1. Put one ice cube on each plate.
  2. Predict: Will salt make the ice melt faster or slower?
  3. Sprinkle a pinch of salt on one ice cube only.
  4. Check every 5 minutes. Which one melts faster? (Do not taste it! Wash your hands after.)

What to look for: The salted ice cube usually melts faster. That is why salt is used on icy roads.

Part 2: My community chart

Talk to a grown-up or look outside. Make a chart with three columns: Change, Helpful or problem?, What people do. Add at least 3 rows, such as "icy sidewalk, problem, spread sand" or "frozen rink, helpful, skating".

Share your chart with your family.

Your turn

1

Name one way freezing helps people.

2

Name one problem that freezing can cause.

3

Why can fish live in a lake all winter?

4

What is a winter road?

5

Why do people spread sand on icy sidewalks?

6

How can too much road salt harm the environment?

More practice: warm-up

1

Is a frozen pond helpful for skating?

2

Can melting snow cause floods?

3

What do polar bears hunt from the sea ice?

4

Is an icy sidewalk safe or unsafe?

5

Where do we keep food to keep it frozen?

More practice: on your own

1

How does a pothole form?

2

What can happen to trees and power lines during freezing rain?

3

Why is ice knowledge from Inuit Elders important?

4

Why might a winter road be open for fewer weeks when winters are warmer?

5

In the salt test, what did we keep the same?

Challenge

1

Give one helpful and one harmful impact of snow melting in spring.

2

Your town wants to use less road salt but keep people safe. Suggest two ideas.

3

Why do people in cold places sometimes leave a tap dripping on a very cold night?

Check your understanding

Quiz

1.

Which is a helpful impact of freezing?

2.

Why can a water pipe burst in a very cold garage?

3.

A winter road can be used...

4.

Why do lakes freeze on the top?

5.

Which is the best choice for an icy step, for people and the environment?

6.

When sea ice melts earlier in the year, polar bears...

For parents and teachers

Big idea: Changes of state have helpful and harmful impacts on people and environments (C1.2). Children connect melting and freezing to real life in Canada: skating, freezers, icy sidewalks, burst pipes, potholes, floods, freezing rain, winter roads and sea ice.

Indigenous perspectives (A3.3): Winter roads are an essential link for some remote First Nations communities in northern Ontario. Inuit have long travelled and hunted on sea ice, and Elders' knowledge of ice safety is passed down through generations. Present these as living, present-day communities.

How to help: On winter walks, point out salt, sand, potholes and icicles. Ask, "What change of state caused this? Is it helpful or a problem? What do people do about it?" If you talk about warmer winters, keep it calm and hopeful: focus on things people can do.

Common difficulties:

  • Not linking burst pipes or potholes to water taking up more space when it freezes. Revisit the freezer cup from the last lesson.
  • Thinking salt is always good. Discuss both sides: safety and the environment.

Safety: Never walk on frozen ponds or lakes unless a grown-up has checked that the ice is safe. Do not taste the salt test.