Drip! Drip! Drip!

If you built and worked with the sundial from the last post, you realized that this kind of clock is not very good for measuring short times because the sun moves too slowly. Around 1500 BCE, the ancient Egyptians developed the water clock, which used steadily dripping water to tell time. You can make a water clock of your own!

What you'll need:
Empty plastic water or soda bottle
Sharp thumbtack or awl
Clear plastic drinking cup (must hold the same amount of water as the bottle, or more)
Water
Marker
Watch with second hand or other timer

With the thumbtack or awl, carefully make a small hole in the bottom of the bottle (an adult should help with this). Fill the bottle with water and check that water drips out slowly (every few seconds). If it takes too long, make the hole bigger. Empty the bottle.

Place the bottle above the plastic cup so that the water falls into the cup. Make sure that the bottom of the bottle is above the bottom of the cup. Now fill the bottle with water again, and measure how much water collects in the cup after two minutes. Mark the two-minute leve on the plastic cup with a line and a "2". Then measure at 4 minutes, 6 minutes, and so on. If your lines are really close together, then measure at 5-minute intervals instead.

Once your water clock has been marked, you can use it to tell time. Pour the water from the cup back into the bottle and set it up again. But instead of timing how long it takes for a certain amount of water to drip out, use the dripping water to time how long something takes. You might see how long it is between commercials on your favorite TV show, or how long it takes to make some food, or how long you can jump up and down!