Classroom · Physics
The paper bridge challenge: strength per gram
Teams load the paper bridges they built until each one breaks. Every result lands on one chart, the bridge's own mass across and the load it held up, under lines of ten to a hundred times its own weight, so the room can see which bridge held the most per gram.
- Groups of 4
A practice run with fictional students. No real classroom or join code is created.
Try an answer on the phone. Lead the lesson from the screen.
On their phone
You are presenting
Setting up the room…
Lesson deck
Teach it as a ready-made lesson
Hook, how it works, the live activity and takeaways. Edit anything.
The paper bridge challenge
A ready-to-teach lesson deck: a hook, how it works, the live activity and takeaways for the debrief.
6 slides · 1 activity
What it teaches
Students compare strength against weight rather than strength alone: the load a bridge held divided by its own mass, read as a slope on the room's own chart, where the winner is the bridge on the steepest line, whether or not it is the heaviest. They test whether strength per gram comes from where the paper goes or from how much of it there is, and connect where their bridges broke to the squeezed top and the stretched bottom of a loaded span.
- Strength-to-weight ratio
- Tension and compression
Debrief, while the boards are still up
- 01
Which bridge sits on the steepest line? Is it the heaviest? Why not?
- 02
Most bridges broke first in one place. What does that say about where to spend your paper?
- 03
The top of a loaded bridge is squeezed and the bottom is stretched. Which did our paper handle better?
- 04
Before testing, most of the room bet on one bridge. What were we judging by?
- 05
If you rebuilt with the same paper, what one change would you make, and which line would it reach?
How it works
- 01
Add it to your library
Sign up free and pull the activity from Decka's built-in classroom catalog — one click copies it into your own library, ready to run from Decka or inside PowerPoint.
- 02
Students join by QR
Everyone scans from the projector and plays in their phone's browser. No app, no account, nothing to install.
- 03
You run the room
You move the activity phase by phase: collection closes, the boards resolve on the big screen, and the debrief happens while the results are still up.
A paper bridge challenge measured per gram
Teams build their bridges before the lesson, all to span the same gap between two tables. In class, each team claims its bridge number on its phones and records three things on one shared team record: the bridge's mass from a kitchen scale, whether the design uses triangles, and the team's guess of how much it will hold. Anyone on the team can fix a typo until the weigh-in closes.
The bridges go on show and everyone walks the gallery, then bets on the one that will hold the most for its own weight. The bets stay sealed until testing ends, so nobody herds onto an early result. Then each bridge is loaded at mid-span, sand poured slowly into a cup on a string until it fails, and its team records the total load it held and where it broke first.
Each test lands on the projector's chart as its team records it: across, the bridge's own mass; up, the load it held. When testing closes, every point becomes the bridge it was, with triangles or without, and the sealed bets open onto the bridges they backed. Lines from the corner mark ten, twenty-five, fifty and a hundred times its own weight, so a bridge on a steeper line held more per gram, whatever it weighed, and the bridge on the steepest is ringed. Next, the rig counts where the bridges broke first, once per bridge, with a bridge that was never tested counted apart rather than as a zero.
The screen shows no bridge numbers: the points are the room's, not a leaderboard. Each phone shows its own team's mass, load, how many times its own weight it held and where that placed it, and whether its own bet called the winner. Try the screen-and-phone preview: the phone is yours, on Bridge 4, and fictional classmates weigh, bet and test through the same runtime as the lesson.
FAQ
Paper bridge challenge questions, answered
What do I need besides phones?
A kitchen scale that reads to the gram, a cup on a string, sand or coins to load it, and two tables set a fixed gap apart. The gap is 30 cm unless you change it in the lesson's settings; the screen's test rig names it, so build to the gap you set.
How do we load the bridges safely?
Pour the sand slowly, so each bridge fails under a load its team can read, and keep feet and hands out from under the cup: when a bridge gives way, the cup and everything in it drops.
How big are the teams?
Up to five people share a bridge, and the lesson plans for four. Each phone joins with its team's bridge number, and a phone that gives a full bridge's number is asked to check it with you. Teams form when the weigh-in opens; anyone who joins after that bets and answers with the room but belongs to no team.
Who records the results?
Each team keeps one shared record for its bridge. One person enters it on their phone, and anyone on the team can correct it until that step closes; a change made from an outdated screen is refused rather than overwriting a teammate's.
Are bridge numbers shown on the projector?
No. The chart and the rig show every tested bridge without its number, and the bets open onto the bridges they backed without numbers too. Every test happens in front of the room, but a list of numbers would turn a lesson about design into a ranking of teams; each phone shows only its own team's results and place.
Why compare per gram rather than the heaviest load?
A bridge with twice the paper can hold more and still be the weaker design. Dividing the load by the bridge's own mass compares how well each one used its material, which is what an engineer is paid to improve.
How long does it take?
Building happens before the lesson. In class, testing takes as long as your bridges do: you move each step on when the room is ready, and no step runs on a timer.
Do students need an app or an account?
No. Students scan a QR code from the projector (or open a link) and play in their phone's browser. Nothing to install and nothing to sign up for.
Does it work in PowerPoint or Google Slides?
In PowerPoint, yes: open the Decka add-in on a slide and choose the Classroom tile. Google Slides is not supported yet; there you present from Decka itself. Students play from their phones either way.
How many students can play at once?
Up to 50 participants per live activity on the free plan, 150 on Pro, and 300 on Badass.
Ready to make your
presentations interactive?
Start free. No credit card required.