Grade 7 · Science · Unit 11 of 14
Safe Structures
Why they fail, how to keep safe
What your child practises
Why structures fail (overloading, fatigue, corrosion, freeze-thaw), choosing materials, how engineers assess and maintain safety, the engineering design process, and social, economic and environmental factors in design, including ergonomics.
Alberta Curriculum learning outcome: Unit D: Structures and Forces · designing safe structures and why structures fail
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
What is the safest way to lift a heavy box?
- Jerk it up quickly
- Bend your knees, keep your back straight and hold the box close
- Bend at the waist and twist while lifting
- Hold the box at arm's length
Show answer
Bend your knees, keep your back straight and hold the box close
Hint: Using your legs and keeping the load close protects your back.
Question 2
Social, economic or environmental factor? Sort each consideration for a new community building.
Sort into: 👥 social · 💰 economic · 🌍 environmental
- 🦉habitat lost on the building site
- 🔧the cost of repairs over 50 years
- ♿ramps and wide doors for wheelchairs
- ♻️using recycled or local materials
- 🧑🤝🧑space where neighbours can gather
- 🧱the cost of materials
Show answer
👥 social: ramps and wide doors for wheelchairs, space where neighbours can gather · 💰 economic: the cost of repairs over 50 years, the cost of materials · 🌍 environmental: habitat lost on the building site, using recycled or local materials
Hint: Social: how it affects people and community. Economic: cost and money. Environmental: effects on nature, materials and energy.
Question 3
An engineer inspects a bridge every two years. Why?
- To make the bridge look new
- To count the cars on it
- To make it lighter
- To find cracks and rust before they become dangerous
Show answer
To find cracks and rust before they become dangerous
Hint: Regular inspections help keep a structure safe.
Question 4
Why does rust weaken a steel bridge?
- Rust makes steel lighter than air
- Rust adds extra strength
- Corrosion eats away the steel, making it thinner and weaker
- Rust removes the bridge's weight
Show answer
Corrosion eats away the steel, making it thinner and weaker
Hint: Paint, coatings and repairs slow corrosion.
Question 5
Concrete is strong when squeezed but weak when stretched. Why is steel rebar put inside it?
- Steel is strong in tension
- Steel is lighter than air
- Steel is weaker than concrete
- Steel makes concrete dissolve
Show answer
Steel is strong in tension
Hint: Combining materials uses the strengths of each.
Question 6
Put the steps of the engineering design process in order.
- 🛠️Plan and build a prototype
- ❓Identify the need or problem
- 📣Improve the design and share it
- 🧪Test the prototype
Show answer
Identify the need or problem → Plan and build a prototype → Test the prototype → Improve the design and share it
Hint: Start with the need, research and brainstorm, build a prototype, test it, then improve and share the design.