We absolutely love bridges here at Raising Sparks. They encapsulate human endevour in so many ways. We were really excited when we saw the pictures of the new Jiaozhou Bay Bridge which opened in Eastern China this week. At over twenty-six miles it is now the longest sea-crossing bridge in the world. It is a stunning and really quite beautiful achievement.
The Jiaozhou Bay Bridge rests on over 5000 bridge supports. The longer spans are cable-stayed. This means a central support takes the force of compression (weight pushing down on the bridge) while the cables stretching out from the bridge support counter the forces of tension (the force which acts on bridge materials making them taut – imagine a rope being pulled by two tug-of-war teams!)
Here is a simple and easy kids science experiment which will enable even the very Littlest Sparks to explore the forces of compression and tension and the importance of understanding these in bridge building.
Materials Needed For This Kids Science Experiment:
Uncooked spaghetti strands of various lengths. (If you can buy the really long spaghetti all the better!)
Something to use as bridge supports. We used food tins from the pantry. We thought the Blue Dragon coconut milk was in keeping with our Oriental theme!
Blue-tack or similar to hold your spaghetti in place.
A large paper clip. Bend it out to form an elongated ’S’ shape.
Metal washers. You could perhaps get away with using small nuts.
A ruler or tape measure to help you record data.
What to do:
Break your spaghetti strands into different lengths. Take your first strand and using the blue-tack attach either end to your bridge supports. Measure the span of your spaghetti bridge. Hook your paper clip over the spaghetti exactly in the middle.
Now thread you metal washers onto the bottom of your paper clip hook one at a time. Do this gently, try not to make heavy weather of it – although in real life bridges do indeed have to contend with whatever the weather throws at them!
Observe the effect as you hang each new washer onto your bridge. How many washers can you add before it breaks altogether? Repeat the experiment with different lengths of spaghetti and make notes.
What did you notice?
At first you may have noticed your bridge buckling (bowing) under the weight of the washers. Buckling is what happens when the bridge can no longer stand the forces of compression acting on it. Eventually the spagetti will snap because it can no longer withstand the tension or stress of being stretched.
Were the shorter stretches of spaghetti able to take more weight? In effect you built a simple beam bridge in this experiment – but there are lots of ways to design a bridge. How could you strengthen the longer spans? Perhaps you could experiment with tying a bundle of spaghetti strands together using wire or cotton. At what intervals do you need to make the ties for a really strong bridge? Can you find a way to make cables to support your bridge? Can you bow the spaghetti at all to make an arch?
Why not use your ideas for a science fair project?