Hamza literally bends over backwards in this episode - in a backbend - to find out why arches are so strong. An arch is a curved shape that spans a space using only gravity to stay up. To find out how it works, we’ll meet a medieval mason, build an arch out of cheese, and sing the praises of buttresses.

INVESTIGATION/HANDS-ON: Han Ru and Stefano find arches in a playground, over windows, and across bridges. They meet up with Haley, an architecture student who shows them how to create the strongest kind of arch -- out of string!

CHALLENGE: Using big blocks decorated to look like cheese wedges, each team has to build a two-metre-high arch that stays up just with gravity – no glue allowed! Then teams put their arch to the strength test by loading water balloons on top. Whoever’s arch is left standing will win glory and wedges of cheese.

BRAIN BENDER: Dara and Skylar go up against Taya and Andrew in today’s crafty brain bender. They’ll create a surprise shape on a loom by hooking coloured elastics to pre-determined pegs. Who can predict what the final shape will be, just by using spatial skills?

EDUCATIONAL TAKE AWAY: Arches are physical structures that span empty space. They are incredibly strong even without being glued together because of “arch action” – the physical forces of gravity. We also touch on symmetry, trapezoidal prisms and different types of arches.