Section 2: Understanding Forces Allows Humans to Build Safe Structures

Key Ideas   Unit Checklist

  Unit D: Section 2 – Introduction


Figure D.S.2.1 – Buildings can collapse if they are not designed to support their weight.

Figure D.S.2.2 – Bridges can collapse if they are not built or maintained properly.

Collapsing Structures

You might hear news stories about buildings or bridges collapsing without warning. These stories are often very sad because many people might be injured or die when a large structure fails.

In 2013, an eight-storey clothing factory collapsed suddenly in Bangladesh. More than 1100 people died and 2500 were injured.

The Bangladeshi government investigated to find why the clothing factory collapsed. Inspectors discovered that the factory’s owner did not follow government rules for building safe structures. The factory was built on sandy ground that used to be a swamp. The factory was supposed to be only five stories tall, but three extra floors were added illegally. Poor quality materials were used to construct the building.

Governments make rules called building codes to help people build safer structures. Building codes are based on scientific understanding of how forces affect the stability of structures. If people follow building codes carefully, tall structures are very stable and safe.


Figure D.S.2.3 – Floors completed collapsed when the structure of this Bangladesh factory failed.

Figure D.S.2.4 – Building collapses can kill and injure many and put rescue workers at risk.

 Watch More

Watch this video to see how a 101-storey skyscraper was constructed in Shanghai, China. This skyscraper is 500 m tall -- that's half a kilometre!



In this section, you will learn more about how forces allow humans to build structures that are stable and safe.


  Words to Think About:

Check the word cloud below. It pictures the important words that you will learn in this section. Watch for these words and combinations of them. When you see them highlighted, click them to learn more about their meanings. You can also visit the course glossary and read definitions for all of these words.
Lessons in This Section

Lesson D5: Forces at Work
Key Question – What are forces and what effect do they have on structures?

Lesson D6: Gravity and Loads
Key Question – How do the centre of gravity and loads affect the strength of structures?

Lesson D7: A World of Bridges
Key Question – How are various types of bridges designed?

Lesson D8: Internal Forces
Key Question – What are internal forces and how do they affect structures?

Lesson D9: Dangerous Forces: When Structures Fail
Key Question – Why do structures sometimes fail?

Lesson D10: Structural Components
Key Question – What shapes and designs are used in strong structures?
Reading and Materials for This Section

Science in Action 7
Suggested Reading: Pages 280–307

Materials Lists for Unit:

  Try It!

Squish the Shape

Try this simple experiment at home.

Materials:

  • toothpicks
  • marshmallows or modelling clay (Plasticine)

Figure D.S.2.5 – These diagrams will help guide your marshmallow constructions.
Part 1: Squish the Square

  1. Make a square with toothpicks, using a marshmallow or modelling clay to connect the toothpicks at the corner (see Figure D.S.2.5.)
  2. Position the square on a table so that it is standing upright. Hold the square so it stays up.
  3. Press down on the top of the square. What do you observe?
Part 2: Squish the Triangle

  1. Make a triangle with toothpicks, using a marshmallow or modelling clay to connect the toothpicks at the corners (see Figure D.S.2.5.)
  2. Position the triangle on a table so that it is standing upright. Hold the triangle so it stays up.
  3. Press down on the top of the triangle. What do you observe?
Part 3: Squish the Square with a Diagonal

  1. Add a toothpick diagonally to your square shape (see Figure D.S.2.5.)
  2. Position the square on a table so that it is standing upright. Hold the square so it stays up.
  3. Press down on the top of the square. What do you observe?
Questions:

Think about the following question very carefully, then type or write your answers. After you have your answer, click the question for feedback.

  • The triangle resisted squishing.
  • The square with a diagonal resisted squishing more than the plain square did.
This is because the square with a diagonal has two triangles inside it. Putting triangles inside a square makes the square shape stronger!