Overview
This lesson covers the basic units of time—seconds, minutes, hours, and days—and explains how to read and understand traditional analog clock faces.
Units of Time
- Time is measured using different units, including seconds, minutes, hours, and days.
- A day is the time it takes for the Earth to rotate once on its axis (24 hours).
- Each day is divided into 24 hours.
- Each hour contains 60 minutes.
- Each minute contains 60 seconds.
Time Unit Relationships and Abbreviations
- 60 seconds = 1 minute.
- 60 minutes = 1 hour.
- 24 hours = 1 day.
- Common abbreviations: d (days), h (hours), min (minutes), s (seconds).
Devices for Measuring Time
- Early time measurement used sundials, which are limited by sunlight and accuracy.
- Modern time is tracked with clocks, which display seconds, minutes, and hours using hands on a face.
How Clocks Work
- Analog clocks have three hands: second (thin, red), minute (long, black), and hour (short, black).
- The clock face usually has 60 marks around the edge for seconds and minutes.
- Each full rotation of the second hand = 1 minute; each full minute hand rotation = 1 hour.
- The hour hand moves past each of 12 hour marks per rotation, representing half a day.
- 12-hour clock cycles are labeled with AM (before noon) and PM (afternoon).
- A 24-hour clock labels hours from 0–23, starting at midnight (0:00).
Reading the Clock
- To read time, note: hour hand (which hour it's past), minute hand (which minute mark, counting by fives), and second hand (exact second).
- Write time as hours:minutes:seconds, separated by colons.
- AM or PM indicates before or after noon.
- Clues (like "morning" or "sunset") may help determine AM or PM.
Examples
- 7:15:00 PM—hour hand past 7, minute hand at 15, second hand at 0, and clue indicates evening.
- 10:20:45 AM—hour hand past 10, minute hand at 20, second hand at 45, clue indicates morning.
- 12:30 AM—hour hand past 12, minute hand at 30, clock is labeled AM (early morning).
Key Terms & Definitions
- Second — The base unit of time; 1/60th of a minute.
- Minute — 60 seconds; 1/60th of an hour.
- Hour — 60 minutes; 1/24th of a day.
- Day — 24 hours; one Earth rotation.
- AM (Ante Meridiem) — The first 12 hours of the day, before noon.
- PM (Post Meridiem) — The last 12 hours of the day, after noon.
- Clock Face — The front circular part of a clock showing time.
- Second hand — Points to seconds on a clock.
- Minute hand — Points to minutes on a clock.
- Hour hand — Points to hours on a clock.
Action Items / Next Steps
- Practice telling time on analog clocks by identifying hours, minutes, and seconds.
- Memorize how many seconds in a minute, minutes in an hour, and hours in a day.
- Try exercises writing time in hours:minutes:seconds format with AM or PM.