Corrugated Paper

Triangles are just plain and boring, right? Wrong! Use the mighty power of triangles to help your plasticine man survive the weight of a block of wood.

Australian Curriculum links

  • Mathematics > Measurement and Geometry > Year 3 > ACMMG063
  • Science > Physical Sciences > Year 4 > ACSSU076

You'll need

  • 2 x A4 sheets of paper
  • 3 blocks of wood
  • plasticine

Try this

  1. Make a house by using two blocks of wood for the walls and a sheet of paper for the roof.
  2. Use plasticine to make a figure of a man that can fit inside the house.
  3. Place the plasticine man in the house and test the strength of the roof by placing the third block of wood on the paper roof. The roof will cave in and the man will be squashed.
  4. Re-shape the plasticine man.
  5. The next step is similar to making a fan. Using the second sheet of paper, fold the shortest end over and make a straight crease, 2 cm from the end.
  6. Fold this 2 cm strip over the other way and repeat folding the paper back and forth until you have folded the whole sheet. Stretch out the paper slightly and use it as the new roof for the house.
  7. Place the plasticine man in the house and test the strength of the roof by placing the third block of wood on the paper roof. The corrugated paper roof is strong enough to support the weight of the wood and the plasticine man is safe.

Further investigation

Experiment with how strong a triangle is by making different types of shapes and testing their rigidity. Use eight paperclips and four straws of the same length to make a shape with four sides. Hook the eight paperclips together in pairs, then thread each of the straws onto a paperclip. Pick the square up and notice how easily it changes shape. Now try making other shapes with three, five or six sides. Notice how the triangle is the only shape that cannot be pushed into a different shape once it is made.

What's happening?

Folding the paper makes a series of triangles, called corrugations. The corrugations make the paper more rigid or stiff, which allows the paper to hold up the block of wood.

The angles of a triangle cannot be changed because each angle is fixed by the side opposite it. This makes triangles a strong shape. Therefore the corrugated paper, with its series of triangles, is able to hold a lot more weight than the flat piece of paper.

Real world links

Triangles are often used in buildings and in other structures that need to be very sturdy. Engineers use triangles to strengthen bridges and buildings that need to support a weight over a large area. The easiest way to do this is to build a truss. A truss is a beam with a series of triangles built inside. It is much stronger and lighter than a solid beam because the triangles provide better support and while leaving lots of open space.

The use of triangles in architecture can be traced back as far as the Ancient Egyptians, Greeks and Romans. The Egyptians used a simple rope tool with a series of twelve knots to trace out right-angled triangles and to create the square bases of the pyramids. The Greeks used trusses in their buildings to support the heavy roofs made of clay tiles. The Romans used a triangle keystone (the centre block of an arch) to create an arch bridge which was capable of withstanding the weight of a marching army.