A River Held Still
Follow the water through a working dam: why its wall is thickest at the base, how falling water becomes electricity, and how the plant answers when a town needs more. Ten investigations for ages 12 and up.
Library
Hold back the lake
Lesson 1
Thin at the Top, Thick at the Foot
A dam’s wall is much thicker at the bottom than at the top. Why does the bottom need so much more concrete?
StartLesson 2
Holes Drilled Under Your Own Dam
Engineers drill drains into the rock under a dam and keep them clear. Why would letting water out from underneath help hold the dam in place?
StartFollow a litre down
Lesson 3
What Is a Metre of Lake Worth?
The lake behind a dam drops, but plenty of water remains. Why can the dam make less electricity even with its water gates just as far open?
StartLesson 4
A Litre's Long Way Down
Water drops a long way through a dam, yet leaves the turbine moving slowly. Why does it not shoot out like water falling off a cliff?
StartLesson 5
What Ate the Steel?
After years of clean, cold water, with no sand to scrape them, a turbine’s steel blades are covered in tiny dents. How can water dent steel?
StartLesson 6
How Fast Can You Stop a River?
A water pipe can bang when a tap shuts quickly. Why could closing a dam’s water gate too quickly burst its pipe?
StartOut to the town
Lesson 7
A Slow Machine for a Fast Number
A generator at a dam turns twice a second, yet its electric current changes direction many times during each turn. How can one turn produce so many changes?
StartLesson 8
The Town Switches On
The dam is the town’s only source of electricity tonight. How does it know when people need more?
StartLesson 9
Half a Million Volts to Boil a Kettle
Electricity for a long journey is sent at an even higher voltage, then lowered again near homes. Why change it twice?
StartLesson 10
Four Calls to the Control Room
A gauge under a dam shows water pushing harder each month, even though the lake stays at the same level. What could make that push grow?
StartReview and assessment
Lesson 11
Test: A River Held Still
Review the course ideas by applying them to new situations, with kind feedback after every answer.
Locked till you take the prior lesson