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How to make a water clock
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Recycle a plastic bottle into this clever clock.

How did people measure time before modern clocks or watches? The ancient Greeks used a water clock called a clepsydra— and you can too in six easy steps. Not only will you learn about this ancient form of timekeeping, but you’ll be doing something good for the environment by reusing an old plastic bottle—awesome!

 

TIP: Make this a family project by getting an adult’s help.

 

What you’ll need:

· Large, clear plastic bottle with a lid

· Scissors

· Compass

· Marker

· Food coloring

· Stopwatch

 

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STEP 1

 

Measure halfway down the bottle, then carefully cut the bottle in two using the scissors. (Don’t forget to ask an adult for help here!)

 

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STEP 2

Unscrew the lid off the bottle and make a small hole in it using the compass. (Get an adult’s help!) Then put the lid back on the bottle.

 

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STEP 3

Turn the top half of the bottle upside down and place it inside the bottom half, so that the lid is facing down.

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STEP 4

Mix a few drops of the food coloring into 16 ounces of water (about two glasses). Have your stopwatch ready!

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STEP 5

Pour the water into the top of the bottle, then start timing. Each time one minute passes, mark a line at the water level of the bottom bottle. (The ancient Greeks used a sundial instead of a stopwatch!)

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STEP 6

Once all the water has passed into the bottom bottle, pour the water back into the top half to use your invention as a clock. Every time the water reaches a line that you marked, you know that one minute has passed! Your plastic bottle has transformed into an ancient timepiece.

Photos by National Geographic Kids

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