Engineering activity
Suspension Bridge
Build a simple hanging bridge using string and cardboard between two chairs. Drive toy cars across it!
Materials and setup
- string
- cardboard
- tape
- popsicle sticks
- cardboard tubes
- scissors
How this changes by age
Pre-K (ages 3–4)
Build a simple hanging bridge using string and cardboard between two chairs. Drive toy cars across it!
Steps
- Place two chairs about 12 inches apart.
- Cut a strip of cardboard for the bridge deck.
- Tie strings from each corner of the cardboard up to the chair backs.
- Adjust the strings until the bridge deck is level.
- Drive a small toy car across. Does it sag? How can you make it stronger?
- Tell a grown-up one thing that surprised you.
Learning objectives
- Understand that strings can hold things up by pulling (tension)
- Observe how weight makes a bridge sag
- Practice tying and adjusting to solve a problem
Kindergarten (ages 5–6)
Build a suspension bridge with towers, cables, and a deck. Test how many toy cars it can hold before the cables fail.
Steps
- Build two towers from cardboard tubes or block stacks, about 18 inches apart.
- Drape a long string over both towers — this is the main cable.
- Cut a cardboard deck and attach shorter strings (hangers) from the main cable down to the deck.
- Space the hanger strings evenly along the deck.
- Test by adding toy cars one at a time. Count how many it holds.
- If it fails, add more hanger strings. Does that help? Draw your bridge and label the parts.
- Tell a grown-up one thing that surprised you.
Learning objectives
- Identify the main parts of a suspension bridge: towers, cables, deck, hangers
- Observe how distributing weight across many hangers strengthens a bridge
- Record test results and make improvements based on observations
Early elementary (ages 6–8)
Engineer a suspension bridge that spans 2 feet and holds a specific weight. Learn about tension, compression, and how cables transfer forces to towers.
Steps
- Research suspension bridges. Identify: main cables, hangers, towers, deck, anchorages.
- Build towers from cardboard tubes reinforced with popsicle sticks. Anchor them to books.
- String the main cable over both towers and anchor each end firmly with tape to heavy books.
- Attach evenly spaced hanger strings from the main cable to a cardboard deck.
- Test with increasing weight. Mark which part fails first — cable, hanger, tower, or deck.
- Redesign the weakest part. Document before and after load capacity.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Explain how tension in cables and compression in towers work together
- Identify failure points in a structural system
- Apply the engineering redesign cycle to strengthen a specific weakness
Upper elementary (ages 8–10)
Design a scale-model suspension bridge with calculated cable tension, tower compression, and optimized hanger spacing. Compare to a beam bridge of the same span.
Steps
- Research how suspension bridges distribute forces. Diagram the force paths.
- Design a bridge spanning 3 feet with labeled measurements and cable angles.
- Build towers, main cables (string), hanger cables, and a cardboard deck.
- Also build a simple beam bridge of the same span using the same total material weight.
- Test both bridges with increasing loads. Record failure point for each.
- Calculate the efficiency ratio for each: max load divided by bridge weight.
- Write a comparison report explaining why suspension bridges can span farther than beam bridges.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Analyze force distribution in tension and compression members
- Compare structural efficiency of suspension vs beam bridge designs
- Calculate and interpret engineering efficiency ratios
Safety and evidence note
Read the full activity before beginning. An adult should supervise tools, heat, food, outdoor work, movement, and experiments as appropriate. Completion records that the activity was done; the child’s explanation, work sample, photo, or demonstration is stronger evidence of learning than a completion check alone.
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