Look at these two joins. Both hold two strips of card together.

• One swings like a gate.
• One locks and will not lean (think of a shelf bracket or a picture-frame corner).

A farm gate needs to swing. A shelf must not. Today we will make the same joint a few different ways, load each one until it fails, and find out which joins hold firm and which let parts pivot.

Those two samples show the big idea: some joins lock, and some joins swing on purpose.

We will make the same simple joint three ways: a sticky-strip wrap, a split pin, and a triangular gusset (a small triangle of card that locks a corner) held with sticky strips. Which do you predict will hold the most load before it fails, and which will swing?

Your group will make the same simple joint three ways so we can compare them fairly.

Then make each join one at a time (listen for the how-to as you reach it):

• 1. Sticky strip: overlap the ends about 2 cm at the V; wrap sticky strip once around the overlap.
• 2. Split pin: use the holes already punched, or wait for the adult at the punch — do not push a sharp pencil through on your own. Open the pin legs flat on the back so the strips can swing.
• 3. Triangular gusset: a gusset is a small triangle of card that locks a corner. Place it across the joint so it covers both strips; fix all three edges with sticky strip so the angle cannot change.

Label each sample. Lay the three ready in a row.

Test one join at a time. Follow this order every time:

1. Hang free: hang the sample from a safe hook or chair back by the free end of one strip so the join hangs in empty air (not pressed against the chair).
2. Check lock or swing: gently try to change the angle at the join. Does it lock or swing?
3. Add coins: add 1c coins one at a time into the hanging cup or on the string loop. Stand clear underneath.
4. Stop: when the join fails, or when you reach 20 coins if it still holds.
5. Jot straight away: on scrap paper write the join name, the coin count, and what moved (peeled, tore, swung, or held). Keep this scrap for the journal write-up next.
6. Next sample: only start the next join after you have written — do not wait until all three are done.

Open your Investigation Journal page. Use your scrap jottings from the load tests. Fill these parts now:

• Our question: write Which join holds the most load before it fails, and how does each fail?
• I predict … because …: finish the stem with the join you thought would hold most (or swing), and one reason.
• What I found out: write one short sentence for each join from your scrap notes. Use the stem The … join held … coins. It failed when the … (or It held 20.).

Leave two blank lines at the bottom of What I found out labelled L before and L after — you will add coin counts there when you strengthen a weak join.

Leave the firm / pivot sort table empty for now — you will fill that next.