How Much Time Does It Take?

MAKE A TIMER!
This activity will demonstrate how to keep track of time using something other than a watch or clock. Students will make a timer that is fun to put together and which they can use to time themselves doing simple activities.

GRADE LEVEL
3 to 5

OBJECT OF ACTIVITY
Make a device that produces regular, steady intervals so you can use it to track time.

CONNECT TO ENGINEERING
In real life, engineers design clocks, watches and timing mechanisms for many purposes, including traffic signal timers that help keep cars moving along city streets, and timing devices for roller coasters.

DISCUSSION
A timer measures the distance between two moments just as a yardstick or meterstick measures the distance between two points. All one needs to make a timer is something that repeats at steady, regular intervals. The second, minute and hour hands on clocks and watches each measure a different unit so we can keep track of different lengths of time. Guide a discussion with students to help them think about time in this way. You may also want to talk about how scientists measure time in different ways. Geologists (people who study the Earth) have ways to measure time over millions of years, and physicists (people who study matter and energy) have ways to measure it in trillionths of a second!

MATERIALS
(for each group of kids)

• 2 clear plastic bottles, caps removed (8 ounce water bottles work well)
• piece of thin cardboard
• pencil
• ruler
• scissors
• masking tape
• 1/2 cup table salt
• funnel watch or clock with second hand

DESIGN AND CONSTRUCTION
Have kids work in small groups of three or four. Before you start, set out the materials needed for each group. Then have the kids work together to make their timers as described here.

1.	Stand the bottle upside down on the cardboard and trace around the bottle opening. Cut out the circle.
2.	Draw a line 3/16 of an inch long in the center of the circle. Poke a hole on the line. Start with a small hole and make it bigger until the diameter is the length of the line.
Note: Steps 3 & 4 may require adult assistance.
3.	Cover the bottle opening with the circle and tape it in place. Be careful not to block the hole!
4.	Using the funnel, pour the salt into the other bottle. Pour slowly so the salt does not irritate your eyes.
5.	Now place the empty bottle on top so both openings meet. Wrap tape around the necks to hold the bottles together.
6.	Use the watch or clock to find out how much time your timer measures. To do this, note what time it is, then turn the timer over so the salt starts to pour down into the bottom bottle. When the last grains of salt pour through, note the time again. How much time has passed? (Each timer should measure between two and three minutes.)
7.	Discuss: How could you make your timer measure a longer time interval? (Add more salt, or make a smaller hole.) How could you make it measure a shorter time interval? (Remove some salt, or make the hole bigger.)

HERE ARE SOME FUN THINGS TO TIME WITH YOUR TIMER:

• See how long you can stand on one foot without losing your balance.
• Have a contest: How many times can you tie or untie your shoe before your timer runs out?
• Have a friend start the timer and, without looking, say when you think the time is up (all the salt has run through).
• Time how long it takes to write your name and address … backwards!

This activity adapted from the Cyberchase:
Math in Science and Engineering Activity Guide, available at www.discoverengineering.org or by contacting Cyberchase at cyberchase@thirteen.org or 877.290.9912.

For more activities visit pbskids.org/cyberchase.
The copyrights in the CYBERCHASE characters are owned by Educational Broadcasting Corporation. CYBERCHASE