An hour glass, also known as a sand glass or a sand clock, keeps time. When the hour glass was invented in the third century in Alexandria, it was sometimes worn like a watch on a chain. The specific length of time each hour glass measures is reckoned by how long it takes the sand inside to run from one bulb to the other. In this activity, your child will make her own sand clock and learn to measure the time it keeps.
What You Need:
- Stopwatch or watch that counts seconds
- Very dry sand or salt
- 2 clean baby food jars (or other small jars) of the same size
- Heavy paper
- Hole punch
- Masking tape
What You Do:
- Pour the very dry sand or salt into one of the baby food jars.
- Using the scissors, cut a piece of heavy paper that will cover the mouth of the jar. Punch a hole in the center of the paper with the hole punch.
- Place the paper over the mouth of the jar. Position the second jar on top of the first, sand-filled jar so that the mouths of the two jars are together with the paper in between.
- Now, tape the mouths of the jars firmly together.
- Turn the jars over and watch the sand fall into the lower jar. How long does it take to fill the lower jar? Turn the sand clock over. Does it take the same amount of time every time?
- Have your child practice predictive thinking by asking how she might change her sand glass to make it measure a different amount of time. How would you build an hour glass so it measures the passage of one hour?