Have you ever wondered how a waterfall forms? When you have a river running over rocks with different rates of erosion, eventually you create a new watercourse: a waterfall! This page shares more about how a waterfall forms, but here are the main points to share with your child:
- A waterfall forms when a river or stream flows over hard rock (where erosion is slow) and also flows over soft rock (where erosion is more rapid).
- As the waterfall gets steeper, it accelerates the erosion as gravity increases the water’s speed.
- Eventually, the watercourse steepens until it’s either nearly vertical or completely vertical. At this point, you have a bon-a-fide waterfall!
This page lists the types of waterfalls and has a helpful graphic that illustrates the formation process. Now, let’s play with the forces of energy that create a waterfall with a simple kinetic energy experiment.
What you need:
What to do:
First, set up your experiment by putting down a sheet or two of watercolor paper near a wall or other surface where you can prop up your yard stick or ruler. Add a few drops of food coloring to a glass of water.
Fill an eye dropper with 1 ml of of the water water and hold it at 4 inches high. Then, drop the water onto the paper. Using the black marker, draw a circle around the splatter.
Move the yardstick a few inches over and repeat the experiment, this time dropping the 1 ml of water from 8 inches. Draw a circle around the splatter.
Finally, repeat the experiment a few inches over, now dropping the water from 12 inches.
Now, use your ruler to measure the size of each splatter circle, or diameter. (diameter definition: The straight-line distance across a circular area, through its center point.) Each time you increase the height of the drop, you increase the distance the drop has to move and add more kinetic energy. Ask your child what happened to the splatter each time you added more kinetic energy. (Answer: The splatters got bigger—the water hit the ground harder and had more energy to travel farther.) We see this same result as falling water continues to form bigger and bigger waterfalls over time!
(+) Try making predictions before getting started. Ask your child:
- What do you think will happen to the size of the splash when
- water is dropped from different heights?
- Will the splash change positions when the water is dropped from a different height?
Use this printable to record your findings.
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