An Introduction to the Units of Time
Everywhere in the world, time is measured using the same system. What exactly is that? How many seconds in a day? What is the SI unit of time? Well, you can see for yourself if you simply look at a watch or a clock. Do you see anything? Minutes and hours are displayed. What else do you notice? Also visible are seconds.
Since they are used to measure time, they are referred to as units of time. The seconds hand travels the fastest, followed by the minute and hour arms if you take some time to observe an extremely old clock with moving arms. Your clock will only display 60 seconds and 60 minutes, as you will also observe.
Units of Time
For hours, just 12 are displayed. When converting between your time units of hours, minutes, and seconds, you must take into account how different the time system operates.
Knowing the Units of Time
Units of Time
The more typical time units are first displayed in the form of a concept web, going from the smallest unit to the largest unit. Start with a second, then move on to a minute, and so on.
The fundamental units of time that we are familiar with are the second, minute, hour, day, week, month, year, century, and millennium. The concept web's second unit is the smallest. We mostly use seconds, minutes, hours, days, weeks, months, and years to measure time:
SI Unit of Time
Measuring Instruments
The second, which is often known as the SI unit of time, is more precisely described as "the time interval equal to 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom". Whatever the case, the unit second is sometimes written as s or sec.
Smallest Unit of Time
Smallest Unit of Time
The smallest unit of time is the second. The base unit of time in the SI unit is second. The following can be used to express all other time units in terms of seconds:
1 minute = 60 s
1 hour = 3600 s and so on.
So, how many seconds in a day?
There are 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day. There are 86,400 seconds in a day because $60 \times 60 \times 24$.
Minutes and Hours to Days Conversion
Hours and Minutes to Days Conversion
Divide the time by the conversion ratio to convert a measurement of an hour to a measurement of a day.
Since 24 hours make up one day, you can convert using the following easy formula:
days = hours ÷ 24
Hours are converted to days by dividing by 24.
For illustration, use the formula above to convert 5 hours to days.
5 hr = (5 ÷ 24) = 0.208333 days
If we want to convert minutes in a day then again we have to divide by 60.
A few units used to measure time are hours, minutes and days.
Solved Example
1. Convert the following:
i) 7 days 6 hours into hours.
Ans: 1 day = 24 hours
$\text { Therefore, } 7 \text { days } 6 \text { hours } =(7 \times 24) \text { hours }+6 \text { hours }$
$=168 \text { hours }+6 \text { hours }$
$=174 \text { hours }$
ii) 5 years 9 months into months.
Ans: 1 year =12 months
$\text { Therefore, } 5 \text { years } 9 \text { months } =(5 \times 12) \text { months }+9 \text { months }$
$=(60+9) \text { months }=69 \text { months }$
Practice Problem
1. Convert the following:
i) 6 hours 40 minutes into minutes.
Ans: 400 minutes
ii) 4 minutes 25 seconds into seconds.
Ans: 265 seconds
Summary
The duration of events or the gaps between them can be measured, compared, or even ordered using time. Units must be specified to measure time; however, there are many possible time units, some of which may be more suitable than others depending on the situation.
Outside of strictly scientific purposes, other units are usually applied for longer durations.
Minute (60 seconds)
Hour (60 minutes, or 3,600 seconds)
Day (24 hours, or 86,400 seconds)
Week (7 days, or 604,800 seconds)
Month (28-31 days, or 2,419,200-2,678.400 seconds)
Year (about 365.25 days, or about 31,557,600 seconds)
FAQs on Units of Time
1. What are the basic units used to measure time?
The most common units of time, often used in daily life and mathematics, are organised from smallest to largest. These include:
- Second: The base unit of time.
- Minute: Equal to 60 seconds.
- Hour: Equal to 60 minutes.
- Day: Equal to 24 hours.
- Week: Equal to 7 days.
- Month: Varies from 28 to 31 days.
- Year: Equal to 12 months or 365 days (366 in a leap year).
2. What is the standard or SI unit of time used in science?
The standard or SI (International System of Units) unit of time is the second (s). It is used globally in science and technology to ensure measurements are consistent. Officially, a second is defined by the vibrations of a caesium-133 atom, making it an extremely precise and reliable standard.
3. How do we convert from a larger unit of time to a smaller one, for example, hours to seconds?
To convert a larger unit of time to a smaller one, you need to multiply. You use the conversion factor that relates the two units. For example:
- To convert hours to minutes, you multiply by 60 (since 1 hour = 60 minutes).
- To convert minutes to seconds, you multiply by 60 (since 1 minute = 60 seconds).
To convert hours directly to seconds, you would multiply by 3600 (60 × 60).
4. What are the units used for measuring very long periods of time?
For measuring time spans that are much longer than a year, we use larger units. The most common ones are:
- Decade: A period of 10 years.
- Century: A period of 100 years.
- Millennium: A period of 1000 years.
5. What instruments have been used throughout history to measure time?
Humans have used various instruments to measure time. Early devices included the sundial, which uses the sun's shadow, and the hourglass or water clock, which measure time by the flow of sand or water. Modern instruments include analog clocks with hands and highly accurate digital clocks and atomic clocks.
6. Why is a 'light-year' not a unit of time, even though it has 'year' in its name?
This is a common misconception. A light-year is a unit of distance, not time. It represents the enormous distance that a beam of light travels in one single Earth year. This is used in astronomy to measure the vast distances between stars and galaxies, which is approximately 9.7 trillion kilometres.
7. How does a standard clock's hands represent different units of time simultaneously?
A standard analog clock uses its hands to show different units of time at once:
- The second hand (usually the thinnest) moves the fastest, completing a full circle every 60 seconds, which equals one minute.
- The minute hand (longer and thicker) completes a full circle every 60 minutes, which equals one hour.
- The hour hand (shortest and thickest) moves the slowest, completing a full circle in 12 hours.
8. Why do we need a 'leap year' with an extra day every four years?
A leap year is necessary because the time it takes for the Earth to orbit the sun is not exactly 365 days; it is about 365.24 days. This extra quarter of a day adds up over four years to become almost a full day. To keep our calendar synchronised with the Earth's orbit and the seasons, we add an extra day, February 29th, nearly every four years. Without leap years, the seasons would gradually drift out of sync with the calendar months.
9. In what real-world situations is it important to use smaller units of time like milliseconds?
While we use seconds, minutes, and hours daily, much smaller units like milliseconds (one-thousandth of a second) are crucial in specific fields. For example, in sporting events like swimming or track races, winners are often decided by milliseconds. They are also vital in scientific experiments to measure rapid reactions and in computer science for processing speeds.
10. How is the official definition of a 'second' determined, and why is it so precise?
The official definition of a second is not based on the Earth's rotation but on a constant of nature: the properties of an atom. It is defined as the time it takes for a caesium-133 atom to oscillate 9,192,631,770 times. This atomic standard is incredibly precise and stable, unlike the Earth's rotation, which can slightly vary. Such precision is essential for modern technology like GPS systems, satellite communications, and the internet, which all rely on perfectly synchronised time.
