# DT (Thursday)

## Introduction to the task

The goats in the ‘Three Billy Goats Gruff’ want some help improving the bridge because it is wonky, old, mossy and the boards are very rickety. They don’t want an arch bridge like the troll wanted. Little Billy goat would like a suspension bridge because its fun and he can see the river, and the troll more easily. Remember to make sure it is well made and safe to use. Can you think of any ways to make the ropes strong so they don’t get all tatty next time? The goats don’t want to cause any more trouble with the troll or wake up.

## Design Criteria

• It must reach between 2 surfaces. (You could set a required length e.g. 40cm but this is optional).
• It must be well made
• They must be able to trot across without falling through it.
• There must be space under it for the troll to live.
• It must be strong enough to hold 3 toys/figures for 30 seconds. If you don't have any figures to test with choose 3 objects of different sizes or build some 'goats' from Lego (see below).

## What are suspension bridges? Let's look at existing ideas.

Look at the photos of suspension bridges in the document below and talk about how they work.

## What are we learning to do?

- build a bridge featuring triangles to help the goats cross the river.

- test our first attempt.

- explore ways to improve our bridge to make it stronger.

- test the model again to see if it is stronger.

## Introduction

The goats have been back in touch. They have decided that they would prefer a more stable bridge. One that won’t sway in the wind or wobble when they walk across it. They want a bridge that is strong enough to hold them all for a long time but they aren’t sure how engineers make bridges stronger. Can you do some research together and help him?

## Introduction

The troll has been in touch and wants to know if you can design an arch bridge so he has more space underneath. The wooden bridge he lives under is too creaky. All he can hear is trip trap, trippety trap!

## Interesting facts about arch bridges

• Arch bridges are very strong.
• Ancient Romans made arch bridges out of stone.
• These bridges were made of columns joined by arches.

## Activity - Making time

### Prepare/gather your materials

Make trapezium shaped blocks ready to build with.

You will need an odd number of block. The same number either side and then the keystone to put in the middle.

- you could use cheese

- you could use cucumber

- you could use apple

- you could use melon

- you could use potato

- you could use salt-dough or playdough and shape the blocks in an ice cube tray or cut it up with a knife.

- You will also need a tube cut in half to support the blocks as shown in the video. You will remove it when all of the blocks are in place. Remember the middle block is added last.

- If you don't have these materials, you can also make arch bridges using recycling. Look below for a document called 'Making arch bridges' below under the heading' Support sheets that will help with making'.

### Health and safety note

An adult might be best preparing blocks for you to use as some foods requires a sharp knife.

Adults - If you have access to soft materials in the list above you could let your child have more input in this stage e.g. sanding sugar cubes with scraps of sandpaper or cutting the corners off cubes of apple or banana you had cut up.

## Testing

Can you count how many weights your bridge can take?

Can you experiment with its size and shape and test it again?

How could you make it stronger/more stable?

Are there other ways you can do it?

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