Welcome, Time Explorer!
Hello! Are you ready to become a master of time? In this chapter, we're going to go beyond just reading a clock. We'll learn some amazing new skills, like using the 24-hour clock, changing hours into minutes (and back again!), and figuring out exactly how long your favourite movie is.
Understanding time is a super important skill for everything in life, from catching a train to planning a fun day out with your family. Let's get started!
Beyond a.m. and p.m.: The 24-Hour Clock
Have you ever seen a time like 15:00 or 21:30 on a train ticket or a digital watch? That's the 24-hour clock! It's a way of telling time that doesn't need a.m. or p.m., which helps avoid any confusion.
How Does It Work?
Instead of the day being split into two 12-hour parts (a.m. and p.m.), the 24-hour clock treats the day as one long journey from start to finish.
- The day starts at 00:00, which is midnight.
- It counts up all the way to 23:59 (one minute before the next midnight).
- Noon is 12:00.
Changing from 12-Hour to 24-Hour Time
Don't worry, it's easier than it sounds! Here’s a simple trick.
For a.m. times (from 1:00 a.m. to 11:59 a.m.):
Just write the time as it is, but make sure the hour has two digits.
Example: 7:30 a.m. becomes 07:30.
Example: 10:15 a.m. becomes 10:15.
Special Case: 12:00 a.m. (midnight) is the start of the day, so it becomes 00:00.
For p.m. times (from 1:00 p.m. to 11:59 p.m.):
Just add 12 to the hour.
Example: For 3:00 p.m., you do $$3 + 12 = 15$$. So, it becomes 15:00.
Example: For 8:45 p.m., you do $$8 + 12 = 20$$. So, it becomes 20:45.
Special Case: 12:00 p.m. (noon) is special. It stays as 12:00. You don't need to add 12!
Changing from 24-Hour to 12-Hour Time
Let's go backwards! This is just as simple.
If the hour is between 00 and 11:
The time is a.m.
Example: 09:45 is simply 9:45 a.m.
Special Case: 00:00 is 12:00 a.m. (midnight).
If the hour is 12:
The time is p.m.
Example: 12:30 is 12:30 p.m.
If the hour is 13 or more:
Just subtract 12 from the hour, and the time is p.m.
Example: For 17:00, you do $$17 - 12 = 5$$. So, it is 5:00 p.m.
Example: For 22:10, you do $$22 - 12 = 10$$. So, it is 10:10 p.m.
Key Takeaway
The 24-hour clock helps us know exactly what time of day it is. Remember the magic number 12! Add 12 for p.m. times, and subtract 12 for times after noon.
Master of Minutes and Seconds!
We know that hours, minutes, and seconds are all related. Now, let's become experts at converting them!
The Golden Rules of Time
Let's do a quick review of the most important time facts. Keep these in your head!
- 60 seconds = 1 minute
- 60 minutes = 1 hour
- 24 hours = 1 day
Big to Small: Multiply!
When you change a bigger unit (like hours) into a smaller unit (like minutes), you multiply.
Analogy: Think of an hour as a big bag of sweets. To find out how many individual sweets (minutes) are inside, you need to multiply!
- To change hours to minutes, you multiply by 60.
Example: 2 hours = $$2 \times 60 = 120$$ minutes. - To change minutes to seconds, you multiply by 60.
Example: 5 minutes = $$5 \times 60 = 300$$ seconds.
Small to Big: Divide!
When you change a smaller unit (like minutes) into a bigger unit (like hours), you divide.
Analogy: You have lots of individual sweets (seconds) and you want to pack them into bags (minutes). You need to divide them into groups!
- To change seconds to minutes, you divide by 60.
Example: 180 seconds = $$180 \div 60 = 3$$ minutes. - To change minutes to hours, you divide by 60.
Example: 240 minutes = $$240 \div 60 = 4$$ hours.
What if it's not a perfect number?
This is where your super-skills come in! Sometimes you'll get a fraction or a decimal.
Example: Let's convert 90 minutes into hours.
We need to calculate $$90 \div 60$$.
As a fraction, that's $$\frac{90}{60}$$, which simplifies to $$\frac{3}{2}$$, or $$1\frac{1}{2}$$ hours.
As a decimal, $$90 \div 60 = 1.5$$ hours.
Both $$1\frac{1}{2}$$ hours and $$1.5$$ hours mean the same thing: 1 hour and 30 minutes.
Did you know?
A leap year happens every four years to help our calendar catch up with the Earth's orbit around the sun. An actual year is about 365.25 days long, so we add an extra day (February 29th) every four years to keep things in sync!
Key Takeaway
To convert time, remember: Big to Small, you Multiply. Small to Big, you Divide. The magic number for converting between hours, minutes, and seconds is always 60!
How Long Did That Take? Calculating Time Intervals
A time interval (or duration) is simply the amount of time that passes between a start time and an end time. Let's learn how to find it.
Finding the End Time
Question: A movie starts at 7:10 p.m. and the duration is 1 hour and 55 minutes. What time does it end?
This can be tricky, but let's break it down.
Step-by-Step Method:
- Add the minutes: $$10 + 55 = 65$$ minutes.
- Deal with the minutes: 65 minutes is more than an hour! We know that 65 minutes = 1 hour and 5 minutes.
- Add the hours: The start hour was 7. The duration was 1 hour. And we have 1 more hour from our minute calculation. So, $$7 + 1 + 1 = 9$$ hours.
- Put it all together: The end time is 9:05 p.m.
Finding the Duration
Question: Art class starts at 9:40 a.m. and finishes at 11:15 a.m. How long is the class?
The easiest way is to "jump" along a number line.
The Time-Jump Method:
- Start at 9:40 a.m.
- Jump to the next "friendly" hour, which is 10:00 a.m. That's a jump of 20 minutes.
- Now jump from 10:00 a.m. to 11:00 a.m. That's a jump of 1 hour.
- Finally, jump from 11:00 a.m. to the end time of 11:15 a.m. That's a jump of 15 minutes.
- Add up your jumps: 20 minutes + 1 hour + 15 minutes = 1 hour and 35 minutes.
Common Mistakes to Avoid!
When you are subtracting time (like 4:10 - 2:50), you might need to "borrow" an hour. Remember, when you borrow 1 hour, you are borrowing 60 minutes, not 100! This is a very common mistake, so watch out for it! Using the 24-hour clock can often make these calculations easier.
Key Takeaway
Finding how long something takes is all about finding the gap between the start and end time. Using a time-jump number line is a great visual way to solve these problems without getting confused. You can do it!