What is time?
Time can be considered to be the sequence of events that occur in succession, from the past into the present, and into the future. Keeping track of time helps us keep track of events that happen in our surroundings. For example, we know when to take the muffins out of the oven because we keep track of every minute. We know when the Sun rises and when it sets because we track the time in hours with respect to the Sun. We know the months in which we can expect rain because we keep track of months. We celebrate our birthdays because we keep track of the number of years we have lived on this planet. Tracking time helps us observe different changes that happen all around us.
Units of time
The basic units of time are seconds, minutes, hours, days, weeks, months, and years. We use seconds, minutes, and hours to tell the time of the day and we use days, months, and years to tell the date. Seconds, minutes, and hours are smaller units of time, and days, months, and years are bigger units of time.
Selecting the unit of time
We choose the unit of time depending on the span of the period we are trying to measure. For example, it is not practical to measure our age in seconds. Similarly, it’s not practical to measure the time between sunrise and sunset in a day, in years. In the former case, we use years, and in the latter case, we use hours.
Converting units of time
To convert time measured in a bigger unit into a smaller unit of time, we multiply the time measured in the bigger unit with a constant. To convert time measured in smaller units into bigger units, we divide the time measure in the smaller unit with a constant. The constant depends on the two units involved in the conversion. The relation between the basic units of time are as follows:
Solved Examples
Example 1: Find the number of minutes in a day.
Solution: A day has 24 hours. We know that an hour has 60 minutes. We must find the number of minutes in 24 hours.
Number of minutes in a day = Number of minutes in 24 hours
= Number of minutes in 1 hour \( \times~24\)
\( =60\times~24\)
=1440 minutes
Therefore, there are 1440 minutes in a day.
Example 2: Find the number of hours in 6 weeks.
Solution: We know that a week has 7 days, and each day has 24 hours. We must find the number of hours in 6 weeks.
Number of days in 6 weeks \( =6\times\) Number of days in a week
\( =6\times~7\)
42 days
So, there are 42 days in 6 weeks.
Number of hours in a day = 24
Number of hours in 6 weeks or 42 days = Number of hours in a day \( \times~42\)
=24*42
=1008 hours
Therefore, there are 1008 hours in 6 weeks.
Example 3: An average human lives up to 70 years. How many months does an average person live?
Solution:
Average human lifespan = 70 years
Number of months in a year = 12
Number of months in an average person’s lifetime = Number of months in 70 years
= Number of months in a year \( \times~70\)
\( =12\times~70\)
=840 months
Example 4: Trevor can run 1 mile in 15 minutes and Isabella can run the same distance in 910 seconds. Who runs faster and by how much?
Solution:
Trevor’s pace = 1 mile per 15 minutes
Isabella’s pace = 1 mile in 910 seconds
To compare their pace, we need to write Isabella’s time in minutes or Trevor’s time in seconds. Let’s write Isabella’s time in minutes.
1 minute is 60 seconds.
Number of minutes in 910 seconds \( =\frac{910}{60} =\frac{91}{6}=15 \frac{1}{6}\)
So, Isabella can run 1 mile in \( 15 \frac{1}{6}\) minutes.
Therefore, Trevor is faster than Isabella by \( \frac{1}{6}^{th}\) of a minute or 10 seconds.
Example 5: George studies for two hours every day. Find the number of hours and the equivalent number of days he spends on studying in a year.
Solution:
Number of hours George spends studying = 2
Number of days in a year = 365 (assuming that it is not a leap year)
Number of hours George spends studying in a year = Number of hours he spends studying in a day \(\times\) Number of days in a year
\(=2\times~365\)
=730 hours
We know that 1 day = 24 hours
Number of days George spends studying in a year \(=\frac{\text{Number of days spent studing in a year}}{\text{Number of hours in a day}}=\frac{730}{24}\)
\(=30~\frac{5}{12}\)
Therefore, George studies for \(=30~\frac{5}{12}\) days in a year.
Year, month, and day are units of time. A year has 12 months or 365 days (366 days in a leap year). A month can have 30 or 31 days (February has 28 days in a regular year and 29 days in a leap year).
Initially, humans started to measure time to keep track of daylight and night-time. This allowed people to be productive when there was light, and also allowed them to prepare for the challenges of surviving darkness. The cycles of the Moon was something that caught the attention of early humans. Then people started tracking weather patterns or seasons to optimize crop production. Across the history of mankind, we have devised different methods to keep track of time. In the modern world, we use simple things like a clock and a calendar to tell time. mastered or which needs more practice.
So we know that a month can have 28, 29, 30 or 31 days. Let’s assume a month to have 30 days. In a week there are 7 days. So let’s divide 30 by \(7,~\frac{30}{7}=4~\frac{2}{7}=4.29\approx 4\). So a month has approximately 4 weeks.