Sand timers are one of the earliest forms of clocks used in history. It’s also an excellent way to demonstrate to children what the passage of time looks like. So, if you’re planning on a trip to the beach, this is a nifty little experiment to help bring along and combine your fun in the sun with a little science.

This experiment will introduce young children to concepts of time, timer, turn over, minute and clock. Although they may have a vague sense of these things, we’re going to make it a visual experience they’ll always remember.

The sand timer that we’re going to construct should measure about three minutes of time, so you can use it over and over again. Kids love to see how fast they are, so why not challenge them to put their toys (or clothes) away before the timer runs out.

You should be aware that you’ll need to do a little prep work before sharing it with the kids. Here’s what you’ll need for the activity:

• Sharp knife
• 2 two liter soda bottles
• 2 liters of dry sand (Very fine sand such as Mississippi river sand takes about 3 minutes to empty)
• Film canister washer (1 inch)
• Stop watch
• Funnel (optional, but definitely helps to keep the mess down if you’re doing it inside the home)

Here’s what you need to do:

1. Fill a two liter bottle full of dry sand
2. With a sharp knife, cut a round hole in each of the lids. (The size of the hole will determine the time it takes for the sand to drain.)
3. Cut the bottom from the film canister about 1 cm from the bottom. You will have an open tube slightly shorter than a film canister.
4. Remove the plastic rings that are left around the necks of the bottles when the lids are removed
5. Connect the full bottle to the empty one. It should all fit together snugly.
6. Turn sand-filled bottle to the top and time with a stop watch

As you visit different beaches and parks this summer, why not try this experiment with different sand. Keep a chart of where you’ve picked up the various sands and then measure how long it takes for the sand to travel from one bottle to the next. Have fun — and don’t forget the sunscreen!

photo credit: conskeptical