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Rocks
- Rock On! - Episode 105
  
Kayaking
 River
Rats Jenny, Danny and Simi brave very rough waters in their kayaks.
They noticed that large boulders appear in some rapids but not
others.
Question
Why are all the boulders in the challenging rapids and not in
the calm waters?
Investigation
Danny, Jenny and Simi explored four different rapids, Class 1
(easy) through Class 4 (challenging). They measured the water
speed at each rapid by measuring the time it took a floating orange
to travel 10 meters. Then they classified the size of rocks they
saw in each rapid.
Results
Jenny, Danny and Simi
found that the bigger boulders were usually found in faster waters.
Here’s what they found.
| rapids |
water
speed
|
rock
size
|
| Class
1 |
0.38
m/s
|
sand,
gravel
|
| Class
2 |
1.1
m/s
|
small
rocks
|
| Class
3 |
0.80
m/s
|
larger
rocks
|
| Class
4 |
1.7
m/s
|
boulders
|
|
Conclusion
They speculated that over centuries of time, fast water carried
smaller rocks and sand further downstream, leaving the boulders
behind. Sand and gravel are deposited in slower waters, leveling
the riverbed and slowing the flow even more. They were surprised
that their Class 3 water speed measurement was slower than the Class
2 measurement.
Rock
Climbing
 Gordon
and Jesse love to scale steep rock cliffs and wondered if studying
rocks would make them better climbers.
Question
How
do different types of rock affect climbing?
Investigation
Gordon and Jesse climbed three different kinds of rock: igneous,
metamorphic and sedimentary. They tested rock hardness, how much
the rocks hurt their hands and whether their feet slipped.
Conclusion
The boys found that rocks that provide good footholds also hurt
their hands (granite and gneiss), while rocks that didn't hurt their
hands also didn't provide good footholds (sandstone).
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