Look at this piece of string and this lolly stick. Which one do you think can push? Which one can only pull? Hands up your guess — we will test it in a moment.

Today we will meet three engineering words: tie, strut and A-frame. You will feel what they mean when you build. First, though, we need to find out what string can do and what a stick can do.

In your group, try four quick tests. Hold both ends of the string and try to push a light book, then pull the book toward you. Do the same with a lolly stick: push, then pull. Talk about what each one can do. You will write it down later. For now, just notice and agree as a group. You may jot a two-word note if you need it.

Your group needs two lolly sticks, a length of string and tape or a split pin. The card on screen gives you the build order, and there is a finished frame on the front desk if you want to check the shape against it.

Work until your frame stands up on the desk on its own. One gentle finger press on the top join is all it takes — this is the moment the words on the board turn into something you can feel, so press lightly and pay attention to your fingers rather than to how much weight the frame will hold.

Record on your Investigation Journal page:

• what string can do and what a stick can do
• which material can only be a tie
• on your A-frame, which part was the tie, which parts were the struts, and how you could tell