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Science Rocks!

Suspension Bridge


your results

Sent in by:
Tyler of GA

How many books can your bridge hold?

Materials Needed

  • 4 chairs with backs
  • 2 9ft. pieces of rope
  • heavy string
  • duct tape
  • cardboard measuring 3ft long by 1.5 ft wide
  • scissors
  • stack of books



  1. Check with a grown-up before you begin.
  2. You will need at least three people to do this activity - two to pull the ropes, and one to place the books on the bridge.
  3. First, put two pieces of rope, each about nine feet long, over the back of two chairs so that the ropes are above the cardboard and run between the chairs.
  4. Now pull the ropes tight.
  5. Bring six equal lengths of string from each rope to the cardboard.
  6. Attach them to the cardboard with duct tape.
  7. Test out your bridge. Put a stack of books on the cardboard.

  1. How many books did it hold?
  2. Here's why your suspension bridge can support the books. The cardboard and the stack of books pull on the strings. The strings pull on the ropes. The ropes push down on the chairs. So, all the weight of the bridge and the stack of books is on the chairs. The rope is also pulling on you. All of the pulling is called tension. And all of the pushing is called compression. What happens if you don't pull as hard on the ropes?

Try making the bridge with a 6 ft by 1.5 ft piece of cardboard instead. How will your design be different? Can it hold more or less weight? Let us know what happened.

Some of your Results

Matthew, age 16 of San Ramon, CA wrote:
I did this once and my bridge didn't collapse. Mine was a 6 ft. platform just like Kaleigh, Aline, Matt, and Garrett used when they did the second challenge of this ZOOMsci on the show.

Marie, age 10 of Sydney, Australia wrote:
It was so strong that my 2 cats and 3 dogs sat on it and it did not move at all.

Maycee, age 10 of Macomb, MI wrote:
Wow! You guys are great! The first time I only got 3 college books on! But when my friends and I switched places we maneged to get on 6 college books!

Jesse, age 8 of Salt Lake City, UT wrote:
I built a suspension bridge. It held lots and lots of books. I got up to 36 light books. It was fun to build.

Bailey, age 6 of Charlevoix, MI wrote:
The bridge was made of two kite strings and two towers. Our kite string was tied to two chairs to keep tension on the line. The bridge was able to hold about 30 pounds.

Jessica, age 11 of Palm Coast, FL wrote:
It fel. But then I remebered something from school. I put popcicle sticks on the bottom.

Emily, age 8 of San Antonio, TX wrote:
My bridge held 92 pounds including bricks and HEAVY rocks. My bridge held 40 things on the 40th thing it fell. But it was a LOT of fun! My bridge was 6 feet 3 inches long and 2 feet 4 inches wide. I used 5 peices of string and 10 peices of tape. My bridge was so strong it could have held my sister. My dad, sister, and I made two bridges and the first one we made worked the best.

T.J., age 11 of Newglasgow, NS wrote:
I made the Suspension Bridge with 6 foot long cardboard. But instead of using 2 9ft rope a used 4. Two on top of the cardboard and two on bottom. I put 8 strings on each side of the cardboard and 8 on the bottom. When I put the books on I could fit 12 books on it before it collapsed. I dare you guys to try it this way.

Katie, age 5 of Beaverton, OR wrote:
We used books and two chairs and a scarf and tape to create a working suspension bridge. We were able to balance a lot of books this way. My little sister and I built it all by ourselves.

Zachary, age 6 of Okemos, MI wrote:
I made the bridge out of straws and tape, and it held up the cup of pennies!

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