D. Structures and Mechanisms · Strong and Stable Structures

Design Challenge: Build a Strong and Stable Tower

A1.3 A1.4 A1.5 D2.3 D2.4 D2.5 D2.7About 50 minutes

Learning goals

I can use the engineering design process to design, build, test and improve a structure.
I can use strong shapes, struts, ties and a wide base in my design.
I can test my structure fairly and record my results.
I can share my design and explain why it is strong and stable.

Words to know

engineering design process
The steps engineers use to solve a problem: ask, imagine and plan, build, test, improve and share.

criteria
What a design must do to be successful. For example, "the tower must be at least 30 cm tall".

constraints
Limits on a design, like which materials you may use or how much time you have.

prototype
A first model built to test an idea.

improve
To change a design to make it work better.

Your challenge

The town needs a new lookout tower so people can see over the trees. You will build a model of it.

Criteria (what it must do):

It must be at least 30 cm tall.
It must hold a load: a full can of soup (or a similar heavy can) on top for 10 seconds.
It must stay standing when you fan it with a piece of cardboard 5 times (the wind test).

Constraints (the limits): you may use only 10 sheets of paper (or newspaper), 1 metre of tape, and 10 drinking straws. You have 30 minutes to build.

A model tower made of rolled paper tubes and tape, with diagonal paper braces, holds a soup can on top on a classroom table. — This model tower uses tubes for strength and triangle braces for stability, and it holds a full can of soup. What would you change in your design? AI-generated image

Remember from Grade 2

In Grade 2 you used the engineering design process to build a machine to move a load. Engineers ask, plan, build, test, improve and share. In Grade 3 you will also think about criteria and constraints, and use what you know about strength and stability.

Step	What you do
1. Ask	What is the problem? What are the criteria and constraints?
2. Imagine and plan	Brainstorm ideas. Draw a labelled plan. Choose the best idea.
3. Build	Build a prototype, following your plan.
4. Test	Measure the height, add the load, do the wind test. Record the results.
5. Improve	Find the weak spot. Change one thing. Test again.
6. Share	Explain your design, results and improvements.

The engineering design process

The engineering design process. Engineers often loop: improve, build and test again until the design meets the criteria.

Use what you know

Everything you have learned in this unit can help:

Strong shapes: roll paper into tubes for columns (struts). Fold paper to make it stiffer. Use triangles.
Struts and ties: add diagonal braces between columns so the frame cannot lean. Tape or string can act as ties.
Stability: make the base wide, keep heavy parts low, and maybe tape the base to a piece of cardboard as an anchor.
Materials: paper is weak flat but strong when rolled. Straws are light but can bend.

Worked example

Let's follow the design process

Here is how Amir solved the challenge.

Ask: The tower must be 30 cm tall, hold a soup can, and survive the wind test. I can use 10 sheets of paper, 1 m of tape and 10 straws.
Plan: I drew a tower with 4 rolled-paper columns at the corners, a wide square base (20 cm on each side) and a smaller top (10 cm). I added straw diagonal braces on each side to make triangles.
Build: I rolled 4 tubes of paper, taped them, and joined them with straws. I made a flat paper platform on top.
Test 1: Height 32 cm. It held the can for only 4 seconds, then one column bent. It passed the wind test.
Improve: I made the columns stronger by rolling them tighter with 2 sheets each. I changed only the columns, so I would know what helped.
Test 2: Height 31 cm. It held the can for 10 seconds. It passed the wind test.
Share: "My tower is strong because rolled tubes are strong columns. It is stable because the base is wide and the braces make triangles."

Amir's tower met all the criteria after one improvement. Finding the weak spot and fixing it is what engineers do.

Amir's tower (front view, not to scale): a wide base, rolled-paper columns and straw braces that make triangles.

Test	Height (cm)	Held the can for 10 s?	Passed wind test?	What I changed
1	32	no (4 s)	yes	first prototype
2	31	yes	yes	rolled columns tighter with 2 sheets each

Amir's results table

Just for fun

Why did the paper tower feel so confident?

It had lots of support: four columns and a whole team of braces!

Hands-on activity

Your design challenge

You need: 10 sheets of paper or newspaper, 1 metre of tape, 10 drinking straws, a ruler or measuring tape, a full can of soup, a piece of cardboard for fanning, a timer, and safety scissors (a grown-up helps).

Ask: read the criteria and constraints out loud.
Plan: draw two different ideas. Label the columns, braces and base. Choose one and explain why.
Build your prototype (30 minutes).
Test: measure the height. Gently place the can on top and count to 10. Fan it 5 times from 30 cm away. Record your results in a table.
Improve: find the weak spot. Change one thing. Test again.
Share: explain your tower to your family: what makes it strong, what makes it stable, and what you improved.

What success looks like: a labelled plan, a tower that meets most or all criteria, a results table, at least one improvement, and an explanation using the words strong, stable, strut, tie or brace. Safety: build and test on the floor, keep your hands and feet out from under the can, place the can gently, and let a grown-up do any cutting.

Your turn

What are criteria?

What are constraints?

Name the six steps of the engineering design process in order.

How could you make paper strong enough to be a column?

Your tower leans when you fan it. Name two ways to make it more stable.

Why should you change only one thing when you improve your design?

More practice: warm-up

What is a prototype?

What is the first step of the design process?

Which shape should your braces make?

Should you test on a table edge or on the floor?

Is a 25 cm tower tall enough for this challenge?

More practice: on your own

Your tower is 34 cm tall but a column bends when the can is placed on top. What is the weak spot, and how could you fix it?

Why is a wide base good for a lookout tower?

Your friend used all 10 sheets in the base and had nothing left for the top. What should they do next time?

Why does Amir's results table have a column called "What I changed"?

Give one way your tower is like a real tower, and one way it is different.

Challenge

Two towers both held the can. Tower A used 10 sheets of paper. Tower B used 6 sheets. Which is the better design for the environment? Why?

New criterion: the tower must also hold the can for 10 seconds while you gently shake the floor mat it stands on (an "earthquake test"). What would you change?

Write a short "share" speech (2 or 3 sentences) for a tower that held the can and passed the wind test.

Check your understanding

Quiz

Criteria are...

Which step comes right after test?

Which would make a paper column stronger?

Diagonal braces help a tower because they...

Only 1 metre of tape is allowed. That is a...

Which is a safe way to test?

For parents and teachers

Big idea: This lesson uses the engineering design process (A1.3): ask, imagine and plan, build, test, improve and share, with criteria and constraints. Your child applies ideas about strength (D2.3), stability (D2.4), materials (D2.5) and struts and ties (D2.7), follows safety rules (A1.4) and shares results (A1.5).

How to help: Let your child lead the planning even if you can see a problem coming. A test that "fails" is a great learning moment: ask "Where is the weak spot? What one thing could you change?" Help with cutting and hold the timer.

What success looks like: a labelled plan, a working prototype, a results table, at least one improvement, and an explanation using unit words (strong, stable, strut, tie, brace, base).

Common difficulties:

Skipping the plan. Ask for a quick labelled drawing first.
Changing many things at once. Encourage one change per test.
Building tall but narrow. Remind them about a wide base and braces.

Safety: test on the floor; place the can gently; keep hands and feet out from under it.