Time - Measuring Duration and Sequence
Time is the ongoing sequence of events that allows us to measure duration, order events, and plan the future. From reading a timetable to calculating how long a journey takes, understanding time measurement is an essential life skill.
Units of Time
| Unit | Relation to smaller unit | Notes |
|---|---|---|
| Second (s) | Base SI unit | Shortest common unit |
| Minute (min) | 1 min = 60 s | |
| Hour (h) | 1 h = 60 min = 3,600 s | |
| Day | 1 day = 24 h | Earth rotation |
| Week | 1 week = 7 days | |
| Month | 28, 29, 30 or 31 days | Varies by month |
| Year | 365 days (366 in a leap year) | Earth orbit |
The 12-Hour and 24-Hour Clock
The 12-hour clock uses am (midnight to noon) and pm (noon to midnight).
The 24-hour clock runs from 00:00 (midnight) to 23:59 and avoids ambiguity. It is used in transport, the military, and medicine.
| 12-hour | 24-hour |
|---|---|
| 12:00 am (midnight) | 00:00 |
| 6:30 am | 06:30 |
| 12:00 pm (noon) | 12:00 |
| 3:45 pm | 15:45 |
| 11:59 pm | 23:59 |
Converting Between Time Units
| Conversion | Operation | Example |
|---|---|---|
| Hours to minutes | × 60 | 2.5 h = 150 min |
| Minutes to hours | ÷ 60 | 90 min = 1.5 h |
| Minutes to seconds | × 60 | 5 min = 300 s |
| Hours to seconds | × 3,600 | 3 h = 10,800 s |
Worked Examples
Convert 3 hours 40 minutes to minutes only.
3 × 60 + 40 = 180 + 40 = 220 minutes.
A film starts at 14:25 and lasts 2 hours 15 minutes. When does it end?
14:25 + 2:15 = 16:40.
Convert 7:30 pm to 24-hour clock.
7 + 12 = 19. Answer: 19:30.
A train departs at 09:15 and arrives at 11:03. How long is the journey?
From 09:15 to 11:03 = 1 h 48 min. Answer: 1 hour 48 minutes.
Key Takeaways
- 1 min = 60 s | 1 h = 60 min | 1 day = 24 h.
- 24-hour clock: add 12 to pm hours; midnight = 00:00, noon = 12:00.
- To find a time interval, count on from the start time to the end time.
Practice Questions
- Convert 2 hours 35 minutes to minutes.
- Convert 245 minutes to hours and minutes.
- A lesson starts at 10:50 am and lasts 75 minutes. What time does it end?
- Convert 8:15 pm to 24-hour clock.
- How many seconds are there in one day?