## Work with Basic Units of Time

Mathematics, Measurement (includes Time)

### Objective

Students review fundamental concepts of time such as A.M. and P.M. and learn about elapsed time.

### Directions

Introduce the activity to students. Use different types of clocks as examples.
Tell students that you are going to review some of the basics of how to tell time. The short hand on the clock indicates the hour while the long hand indicates the minutes. Not only do the numbers on the face of the clock indicate what hour it is but they also indicate the number of minutes in each hour. Starting at the 12, you have to count by 5's, going around the clock until you again reach the 12. Keep in mind that an hour is made up of four quarters. Each quarter is 15 minutes long. When the time is 15 minutes past the hour, it can be read as quarter past the hour (Example: 2:15 is also a quarter past 2). When the time is 15 minutes before the next hour, the time can be read as quarter 'til the hour (Example: 2:45 or quarter 'til 3).
To keep track of the minutes and hours during the day and night, we use several devices. A wristwatch with a second hand counts oscillations in a little wheel that rocks back and forth. A grandfather clock counts swings of the pendulum. A digital watch counts electronic oscillations in a quartz crystal. All of these are fairly accurate, but they all must be adjusted once in a while.
One of the most accurate clocks is the digital clock which plugs into a wall socket. Digital clocks count cycles of 60-cycle electrical power. You might think that the power company is not in the time business, but it is!
Elapsed Time
You can calculate how much time has passed or elapsed from the beginning of an activity to its end.
Sample
Monica and Eli went to the beach. They left their house at 9:30 a.m. If they got home at 3:00 p.m., how much time elapsed?
From 9:30 a.m. to 12:00 p.m., 21/2 hours elapsed.
From 12:00 p.m. to 3:00 p.m., 3 hours elapsed.
Add 21/2 hours to 3 hours. So 51/2 hours elapsed from the time Monica and Eli left their house to when they came back home.
Use the time conversion table below to help you work out the problems on the pages in this unit.

Time Table

60 seconds = 1 minute

7 days = 1 week

60 minutes = 1 hour

52 weeks = 1 year

24 hours = 1 day

a.m. is the time from midnight to noon.

p.m. is the time from noon to midnight.

10 centuries = 1 millennium

### Resources

• Working with Basic Units of Time activity sheets
• pencils
• different types of clocks