Original notes — ready
Chapter 12: Racing Seconds
CBSE (NCERT, English Medium) • Class 5 • Mathematics • Book: Math Mela
Racing Seconds — EG's own notes, in simple words
Book: Math Mela (CBSE, Class 5) | Chapter 12 | Medium: English
Diagram (labels are printed on the image): A stopwatch, a running track and a runner. A general teaching picture about seconds; no wall clock is shown in this picture.
Children racing on a school track. A general picture about races and time.
What the chapter is about
This chapter is about time in seconds. A second is a very short time — you can clap once in about a second. 60 seconds make 1 minute; 60 minutes make 1 hour.
Races are timed in seconds: a 100-metre sprint may take 15 seconds, and the winner is decided by even a single second. Stopwatches measure seconds and parts of a second.
The chapter teaches converting between hours, minutes and seconds, and comparing times: smaller time means faster in a race.
Seconds matter beyond races too. Doctors count heartbeats in a minute, cooks time boiling eggs in minutes and seconds, and musicians keep time in beats per minute. Small units help us measure short events exactly.
What you should learn
Time conversions use 60, not 100: 1 minute = 60 seconds, 1 hour = 3600 seconds. Keep the 60-times table ready.
Key Terms
- Second — A very short unit of time.
- Stopwatch — A watch that measures time precisely.
- Race — A competition of speed.
- Convert — To change from one unit to another.
- Faster — Taking less time to finish.
- Pulse — The steady beat felt in the wrist, counted to check how fast the heart beats.
Remember
- 1 minute = 60 seconds; 1 hour = 60 minutes = 3600 seconds.
- In a race, less time means faster.
- Stopwatches measure seconds and parts of seconds.
- Convert before comparing times.
Exam Tip / Common Mistake
Common mistake: writing 2 minutes 30 seconds as 2.30 minutes. It is 150 seconds (2 × 60 + 30).
Chart / Table: Time conversions
| Unit | Equals |
|---|---|
| 1 minute | 60 seconds |
| 1 hour | 60 minutes |
| 1 hour | 3600 seconds |
| 2 minutes 30 seconds | 150 seconds |
Think and try
Clap once every second for 10 seconds while a friend counts. Was it hard to keep steady? Now count your claps in 30 seconds and double the number. How many claps would that be in one minute?
Practice set — try it yourself
- How many seconds are in 3 minutes?
Hint: Multiply by 60. - Convert 200 seconds into minutes and seconds.
Hint: Divide by 60. - Ravi runs in 18 seconds, Meena in 15 seconds. Who is faster?
Hint: Less time wins. - A race starts at 10:00:00 and ends at 10:00:45. How long did it take?
Hint: Subtract. - How many seconds are in 1 hour?
Hint: 60 × 60.
How to use this page: Read the summary, say the Key Terms in your own words, then try the practice set without looking. Ask your teacher or parent to check your answers.