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D. Structures and Mechanisms · Forces Acting on Structures

Forces Acting on Structures: Unit Review

A1.1 A1.2 A1.3 A1.4 A1.5 A2.1 A2.2 A3.1 A3.2 A3.3 D1.1 D1.2 D2.1 D2.2 D2.3 D2.4 D2.5About 40 minutes
Learning goals
  • I can identify internal and external forces and describe their effects on structures.
  • I can describe forces from natural phenomena and the features and materials that help structures withstand them.
  • I can describe how plants, animals and protective equipment protect against harmful forces.
  • I can analyse and assess how communities deal with nature's forces.

Words to know

internal force
A force inside the parts of a structure: compression, tension, torsion or shear.
external force
A force acting on a structure from the outside, like gravity, wind or snow.
dynamic load
A load that moves or changes quickly.
cross-bracing
Diagonal braces in an X that turn a frame into triangles.
mitigate
To make something less harmful.

Let's review!

In this unit you learned the four internal forces, sorted external loads into static and dynamic, studied how nature's forces can damage structures and how features and materials help them withstand those forces, found protective characteristics in plants and animals, explained how protective equipment works, analysed effects on natural and built environments, assessed how communities mitigate damage, and designed your own shake-proof tower. This review has a few questions from every lesson. Try each one, then press Show answer to check. If a part feels tricky, go back to that lesson for more practice.

In natureIn buildingsturtle shell (dome)arena dome rooftree roots (anchor)building foundationhollow grass stembicycle frame tubemussel threads (tension)guy wires on a tower
Engineers borrow ideas from nature: domes, anchors, hollow tubes and cables in tension.
Match the force to the features that resist itSideways pushwind, earthquakesX-bracesshear wallsbase isolationDownward pushheavy snow, icesteep roofsstrong trussesmore bracingWaterfloods, erosionraise on postsdeep foundationsflood walls, dikes
Each kind of force from nature has its own set of structural features that help buildings withstand it.

Internal Forces: Compression, Tension, Torsion and Shear

1

Name the four internal forces.

2

A towel being wrung out feels which internal force?

3

A beam bends under a load in the middle. Which side is stretched?

4

What can too much compression do to a long, thin column?

External Forces: Static and Dynamic Loads

1

Static or dynamic: trucks crossing a bridge?

2

Static or dynamic: the weight of the bridge itself?

3

Why does a dropped box push harder on a table than one set down gently?

Nature's Powerful Forces: Danger for Structures

1

Which internal force causes X-shaped cracks in walls during earthquakes?

2

How can wind damage a roof?

3

How can a flood damage a building without knocking it over?

4

Why do potholes form in spring?

Built to Last: Features and Materials That Withstand Nature's Forces

1

How does cross-bracing help a frame?

2

What is base isolation?

3

Give one feature that helps a building in a flood area.

Nature's Engineers: How Plants and Animals Withstand Forces

1

How does a turtle's domed shell protect it?

2

How do roots help a tree in the wind?

3

Why do many grass stems bend in the wind instead of breaking?

Protective Equipment: Helping Our Bodies Withstand Forces

1

Name two ways protective equipment protects us.

2

What does a helmet's foam do?

3

Why should a bike helmet be replaced after a crash?

Nature's Forces on Natural and Built Environments

1

Is a sand dune part of the natural or built environment?

2

Give one short-term effect of a windstorm on people.

3

How can a windstorm help a forest?

Protecting Communities: Urban, Rural and Remote

1

What does mitigate mean?

2

How does a snow fence help a rural highway?

3

Why are many northern buildings raised on piles?

4

Name two criteria for assessing a solution.

Design Challenge: A Structure That Withstands Shaking and Wind

1

What are the steps of the engineering design process?

2

A tower survives 20, 24 and 22 shake rounds. Find the average.

3

Why change only one thing when improving a design?

Just for fun

Riddle: Why did the engineer bring string to the party?

In case things got a little tense!

How to use this review

  • Do the review in two short sittings. Each section matches one lesson.
  • Say your answers out loud using science words: compression, tension, torsion, shear, static, dynamic, mitigate.
  • For "why" questions, always name the force and what it does.
  • Put a star next to any question you got wrong, and go back to that lesson's practice and activity.
Check your understanding

Quiz

1.

Which internal force stretches a material?

2.

Scissors cut paper using...

3.

Which is a dynamic load?

4.

Which natural phenomenon damages structures mainly by erosion of the ground beneath them?

5.

Why do X-braces made of thin cables work against wind from either side?

6.

Which physical characteristic helps a tree withstand strong wind?

7.

How does a helmet's hard shell protect you?

8.

Which is a natural structure that waves can wear away?

9.

Why are many buildings in the far North raised on piles?

10.

A tower survives 16, 20 and 24 shake rounds. What is the average?

For parents and teachers

Use mistakes to choose what to revisit. Each review section matches one lesson.

  • Mixes up compression, tension, torsion and shear, or can't explain bending: revisit Internal Forces: Compression, Tension, Torsion and Shear and redo the sponge model.
  • Can't tell static from dynamic loads, or confuses them with dead and live loads: revisit External Forces: Static and Dynamic Loads.
  • Can't link a natural event (earthquake, wind, snow, ice, flood, freeze-thaw) to the forces it causes: revisit Nature's Powerful Forces: Danger for Structures.
  • Can't name features or materials that help structures withstand these forces, or gets the X-brace direction wrong: revisit Built to Last: Features and Materials That Withstand Nature's Forces and redo the brace test.
  • Says plants and animals are "strong" without saying how (dome, anchor, flexible, hollow tube): revisit Nature's Engineers: How Plants and Animals Withstand Forces.
  • Can't explain how equipment protects (spreads, cushions, holds, shields): revisit Protective Equipment: Helping Our Bodies Withstand Forces.
  • Forgets natural structures, or sees only harmful effects: revisit Nature's Forces on Natural and Built Environments.
  • Can't name mitigation strategies for urban, rural or remote communities, or assesses only by "it works": revisit Protecting Communities: Urban, Rural and Remote.
  • Struggles with averages or changes many things at once when testing: revisit Design Challenge: A Structure That Withstands Shaking and Wind.

A few mistakes are normal. Praise explanations that name a force and what it does, not only correct answers.