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Kayaking by Jenny, Simi and Danny

We think of rapids as nature's roller coasters. They're fast, fun and furious. But we always wondered: Why are there different rocks in different rapids? To sort it all out, we headed for the ultimate thrill ride that included not only rapids, but also a waterfall!

What did we do?
We compared four classes of rapids: Class 1, Class 2, Class 3 and Class 4. We looked at what kind of rock was in each rapid. Then we figured out the speed of the water. We used an orange and timed how long it took the orange to float 10 meters. We divided the length, 10 meters, by the time and got the speed. We recorded the water speed and made observations about why different types of rocks were in each rapid

What did we find out?
We found out that Class 4 rapids had the fastest water speed. In fact, the water moved so fast, the orange slipped past Simi. He had to chase the orange over a waterfall! We also found out there were big boulders and bedrock in Class 4 rapids. We thought about the relationship between the rock and water speed and figured out boulders are too big to be easily moved by the water. But the gravel and small rocks are easily picked up and sent downstream to a slower moving part of the river.

Class Water Speed
(Distance/Time = Speed)
Rock type
Class 1 10/26.23 = .38 Sand & Gravel
Class 2 10/9.43 = 1.1 Medium rock
Class 3 10/12.45 = .80 Stones
Class 4 10/5.95 = 1.7 Boulders & Bedrock

What can you do?
  • Why not check out a river near your house? Can you see any correlation to water speed and what's in the river? When you do your test, make sure an adult is watching you! And always wear a life jacket!
  • What other speeds can you measure? What about your favorite sledding hill? What's the fastest hill? Remember you get speed by dividing distance by time. Distance / Time = Speed.
  • Jenny, Simi and Danny used observation of the rocks and compared that to the results of their speed experiment. How else can you use both observation and experimentation?
  • Use this kayak investigation as a science fair project idea for your elementary or middle school science fair! Then tell us about it!
more resources
More on the Geologic Time Scale

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