Grade by Grade
D. Structures and Mechanisms · Forces Acting on Structures

Nature's Forces on Natural and Built Environments

D1.1 A1.1 A1.5 A3.1About 40 minutes
Learning goals
  • I can analyse how forces from natural phenomena affect natural structures like cliffs, forests and riverbanks.
  • I can analyse how these forces affect built structures like roads, power lines, docks and houses.
  • I can describe effects on people and on the environment, both short-term and long-term.
  • I can use an analysis chart to organize my thinking.

Words to know

natural environment
The parts of the world made by nature: land, water, rocks, plants and animals.
built environment
The parts of the world made by people: buildings, roads, bridges, power lines and parks.
natural structure
A structure made by nature, like a cliff, a tree, a riverbank, a sand dune or a beaver dam.
analyse
To look closely at something, part by part, to understand how and why it happens.
short-term effect
An effect that happens right away and doesn't last long, like a power outage for a day.
long-term effect
An effect that lasts a long time or appears slowly, like a cliff wearing back over hundreds of years.

Forces shape the world

The same forces that push on buildings also push on natural structures: cliffs, trees, riverbanks, sand dunes and beaver dams. Some changes take a few seconds, like a tree blown over in a storm. Others take hundreds or thousands of years, like waves slowly carving rock.

Today you will analyse (look closely at) how forces from natural phenomena affect both the natural environment and the built environment, and what that means for people and other living things.

Effects on natural structures

  • Rock shaped by waves: at Flowerpot Island in Georgian Bay, waves and weather have worn away rock over a very long time, leaving tall rock pillars called "flowerpots". Waves, rain and ice keep wearing them away today.
  • Forests: strong winds and ice storms snap branches and blow down trees. This can look like destruction, but it also has helpful effects: fallen and dead trees become homes for insects, woodpeckers and other animals, and new sunlight reaches young plants on the forest floor.
  • Riverbanks: floods erode riverbanks, carry soil downstream, and can even change where a river flows. The soil can make the water muddy, which affects fish and other water life.
  • Beaver dams: a big flood can push hard enough to break a beaver dam. The beavers rebuild.
  • Sand dunes: wind pushes sand and slowly moves and reshapes dunes.
A tall limestone rock pillar, wider at the top, with cedar trees on top, standing in clear turquoise water by a rocky shore.
Rock pillars like this "flowerpot" on Georgian Bay were shaped very slowly as waves, rain and ice wore away the softer rock at the bottom. AI-generated image
How waves can carve a rock pillar (simplified)crackwaves wear a notchweak rock and cracks wear awaya pillar is left standingThis takes a very, very long time. Not to scale.
Waves, rain and ice slowly wear away the weaker rock, and a tall pillar of harder rock can be left behind, like the "flowerpots" of Flowerpot Island.

Effects on built structures

  • Power lines and towers: ice storms and windstorms can bring them down. In May 2022, a powerful windstorm called a derecho swept across southern Ontario and Quebec, knocking down trees, power poles and transmission towers.
  • Roads and sidewalks: freezing and thawing make potholes and cracks every spring.
  • Docks and shorelines: in spring, wind can push large sheets of lake ice onto the shore. The ice can push docks out of place and damage shoreline buildings.
  • Houses: floods can fill basements and damage foundations. Heavy snow can make roofs sag. Wind can tear off shingles.
  • Bridges and culverts (pipes that carry streams under roads) can be washed out by floods.

Effects on people and the environment

When structures are damaged, the effects spread:

  • Short-term: power outages, closed roads, flooded homes, people staying with friends or in emergency shelters, danger from fallen wires.
  • Long-term: the cost of repairs, communities rebuilding, people moving away from risky areas, and changes to habitats.
  • Environment: fallen trees, debris washed into rivers and lakes, eroded soil, and new habitats forming.

Scientists expect climate change to bring more extreme weather to some places, which makes this kind of analysis even more important.

StepQuestion to ask
1. EventWhat natural phenomenon happened?
2. ForceWhich forces did it put on structures? (push, pull, weight, shaking, erosion)
3. StructureWhich natural or built structures were affected, and how?
4. PeopleHow were people affected? Short-term? Long-term?
5. EnvironmentHow were plants, animals, land and water affected?
An analysis chart you can use for any natural event
Worked example

Let's analyse a spring ice push on a lake

In spring, strong winds push a thick sheet of melting lake ice onto the shore near some cottages. Analyse the effects.

  1. Event: wind pushes lake ice onto the shore during spring break-up.
  2. Force: the huge, heavy ice sheet pushes sideways on the shore. This is a large dynamic load.
  3. Structures: built: docks are pushed out of place or broken; a boathouse wall may be cracked. Natural: the shoreline is scraped, rocks are moved and soil is pushed up into ridges.
  4. People: short-term: cottagers can't use their docks; long-term: the cost of repairs, and they may build docks that can be removed before winter.
  5. Environment: shoreline plants are scraped away; soil may wash into the lake.

The ice's sideways push damages both built structures (docks, boathouses) and the natural shoreline, with short-term and long-term effects on people and the lake.

Analysing a spring ice pushEventwind pusheslake ice ashoreForcehuge sidewayspush (dynamic)Structuresdocks broken,shore scrapedPeoplerepairs costmoney and timeEnvironmentshore plantsscraped away
The five steps of the analysis chart, filled in for the ice push example. Follow the arrows from the event to its effects.
Worked example

Let's compare a windstorm in a forest and in a town

A strong windstorm hits a forest and a nearby town. Compare the effects.

  1. Forest (natural): trees blow down and branches snap (too much bending). Some animals lose homes, but fallen trees become new homes for others and sunlight reaches young plants. The forest slowly regrows on its own.
  2. Town (built): shingles and roofs are torn off (wind lifts), power lines come down, and fallen trees damage cars and houses. People lose power and must pay for repairs. The town needs people to rebuild.
  3. Same: the same force (wind) bent and broke structures in both places.
  4. Different: the forest recovers by itself over many years; the town needs repair crews right away.

The same wind force harms both, but a forest recovers naturally (and gains new habitats), while a town needs people to repair it, at a cost.

Just for fun

Beavers are nature's repair crew. When a flood breaks their dam, they don't call anyone: they just get back to work, one stick at a time!

Hands-on activity

Forces detective walk and erosion model

Part 1: Walk (with a grown-up). Walk around your neighbourhood or a park. Look for evidence of natural forces on structures:

  • cracks or potholes in sidewalks and roads (freeze and thaw)
  • leaning fences, signs or trees (wind, soil movement)
  • broken branches or fallen trees (wind, ice, snow)
  • bare soil washed away on a slope or beside a ditch (water erosion)

Make a chart with columns: What I saw, Natural or built?, Force that caused it, Effect on people or the environment. Find at least 5 things.

Part 2: Erosion model. You need: a baking tray, sand or soil, a small plastic cup, water, and a small block or toy house.

  1. Pile the sand into a hill at one end of the tray. Put the toy house near the edge of the hill.
  2. Slowly pour a cup of water over the top of the hill, like heavy rain.
  3. Pour faster to model a flood.
  4. Record what happens to the hill and the house.

What to look for: water carves channels, carries sand downhill, and eats away the ground under the house until it tilts or slides. This shows how erosion damages foundations.

Safety: on your walk, look but don't touch. Stay away from fallen wires, broken structures and fast water. Do the erosion model outside or in a sink area.

Your turn

1

What is the difference between the natural environment and the built environment?

2

Name two natural structures that forces from nature can change.

3

How do waves change rock over time?

4

Give one short-term and one long-term effect on people of an ice storm.

5

Can a natural event have a helpful effect on the natural environment? Give an example.

6

Name the five steps of the analysis chart.

More practice: warm-up

1

Is a beaver dam a natural or a built structure (built by people)?

2

Is a culvert a natural or built structure?

3

What can a flood do to a riverbank?

4

What natural force makes potholes?

5

What does analyse mean?

More practice: on your own

1

Why does a forest recover from a windstorm differently from a town?

2

When a flood washes soil into a river, how can this affect the environment?

3

How can the same windstorm affect people in two different ways in the short term and the long term?

4

Choose a natural event from this unit and fill in the Force step: what forces did it put on structures?

5

In the erosion model, what happened to the toy house? What real-life problem does this show?

Challenge

1

Explain why a change can be good for one living thing and bad for another, using a fallen tree as the example.

2

Waves have worn away rock at Flowerpot Island over a very long time. Is this a short-term or long-term effect? What might happen to the pillars far in the future?

3

Use the analysis chart to analyse a heavy snowstorm in a town. Write one sentence for each step.

Check your understanding

Quiz

1.

Which is a natural structure?

2.

What slowly carved the rock pillars at Flowerpot Island?

3.

Which is a long-term effect of a big flood on a town?

4.

How can a windstorm help a forest?

5.

In spring, what can wind-pushed lake ice do to docks?

6.

Which step of the analysis chart asks "How were plants, animals, land and water affected?"

For parents and teachers

Big idea (D1.1): Students analyse the effects of forces from natural phenomena on structures in both natural environments (cliffs, forests, riverbanks, dunes, beaver dams) and built environments (power lines, roads, docks, houses, bridges), including short- and long-term effects on people and the environment. The walk and the analysis chart practise research and communication (A1.1, A1.5) and connect to the home and community (A3.1).

How to help: Use the five-step chart (Event, Force, Structure, People, Environment) when you hear about a storm on the news. Ask, "Who was affected? Was any effect helpful?"

Common difficulties:

  • Seeing all effects as bad. Point out that natural disturbances also create habitats.
  • Forgetting the force step. Ask, "Was it a push, a pull, extra weight, shaking or erosion?"
  • Worry: reassure children who are anxious about storms that communities have plans, warnings and crews to keep people safe (the next lesson explores this).
  • Safety: on the walk, look but don't touch, and stay well away from fallen wires and fast water.