Time is used to measure the duration of a phenomenon, the period between 2 events.
On Earth, time and its units are based on the rotation of the Earth and the Earth’s revolution around the Sun. Time can be measured using a watch or a stopwatch.
The system for units of time is not based on the same model as other units of measure. Specifically, it is not formed using a base of 10. Special care must be taken when converting the units of measurement of time.
The base time unit, in the International System of Units (SI), is the second.
There are several units for expressing time:
Each unit of time has a specific value.
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One year is the time it takes for the Earth to revolve around the Sun once. One year has 12 months, 52 weeks or 365 days (365.25 days to be exact).
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One month is 1/12 of a year. A month is about 4 weeks and is usually 30 or 31 days long.
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One day is the time it takes for the Earth to rotate once on its axis. One day is 24 hours long.
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One hour is a unit of time that divides one day into 24 equal parts. There are 24 hours in a day.
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One minute is a unit of time that divides one hour into 60 equal parts. There are 60 minutes in an hour.
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One second is a unit of time that divides one minute into 60 equal parts. There are 60 seconds in a minute.
This is summarized in the following table:
A year is usually made up of 365 days, but that is not quite true. A year is actually 365.25 days long. Every 4 years, we end up one day behind. This is why a 366th day was added to every fourth year: this is called a leap year.
Months are not all the same length: they are an approximate measurement. A month usually has 30 or 31 days, except for February, which has only 28 days (29 days on leap years).
Some events recur periodically, meaning regularly over time. The temporal cycle of these events is given various qualifiers.
An annual cycle is a phenomenon that occurs every year.
A monthly cycle is a phenomenon that occurs every month.
A weekly cycle is a phenomenon that occurs every week.
A daily cycle is a phenomenon that occurs every day.
To change from one unit of time to another, it is important to know the following proportions:
How many minutes are there in 4 hours and 40 minutes?
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First, convert 4 hours into minutes. ||\begin{align}\dfrac{1\ \text{h}}{4\ \text{h}}&=\dfrac{60\ \text{min}}{x}\\\\ x&= 4\times60\div 1\\ &=240\ \text{minutes}\end{align}||
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We add this result to the minutes present in the starting situation.||240 + 40 = 280\ \text{minutes}||
Answer: There are 280 minutes in 4 hours and 40 minutes.
How many seconds are there in a leap year?
To solve this problem, take a step-by-step approach.
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There are 366 days in a leap year.
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There are 24 hours in a day. ||\begin{align}\dfrac{1\ \text{d}}{366\ \text{d}} &=\dfrac{24\ \text{h}}{x}\\\\ x&=366\times24\div 1\\ &=8784\ \text{h}\end{align}||
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There are 60 minutes in 1 hour.||\begin{align} \dfrac{1\ \text{h}}{8784\ \text{h}} &=\dfrac{60\ \text{min}}{x}\\\\ x&=8784\times 60\div 1\\ &=527\,040\ \text{minutes}\end{align}||
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There are 60 seconds in 1 minute. ||\begin{align}\dfrac{1\ \text{min}}{527\,040\ \text{min}}&=\dfrac{60\ \text{s}}{x}\\\\ x&= 527\,040\times60\div 1\\ &=31\, 622\,400\ \text{seconds}\end{align}||
Answer: There are 31 622 400 seconds in a leap year.