What Is Second?
A second is the main unit people use to measure time. It is a very short period, but many seconds together make minutes, hours and days.
Definition
In simple words, one second is a tiny slice of time. Sixty seconds make one minute.
Scientists use a very exact definition. They say one second is the time it takes for a special kind of light from a cesium 133 atom to vibrate 9,192,631,770 times. This sounds complex, but it helps keep the length of a second exactly the same everywhere.
The second is the base unit of time in the International System of Units, called the SI system. All other common time units, like minute and hour, are built from seconds.
History / Origin
Long ago, people used the Sun to tell time. They divided the day into 24 hours, each hour into 60 minutes and each minute into 60 smaller parts. Those smallest parts became what we now call seconds.
For many years, a second was based on the length of a day on Earth. One second was one eighty six thousand four hundredth of the time between one noon and the next noon.
Later, scientists found that Earth does not spin at a perfectly steady speed. This made the old kind of second a little uneven. To fix this, in the 1900s they started using very steady atomic clocks. In 1967, they agreed on the modern definition that uses the cesium atom. This atomic second is the one used today in science, GPS and world time.
Symbol & Abbreviation
The official symbol for second is s.
Other short forms you may see are:
- sec sometimes used in writing
- ″ double prime symbol in some old texts, but this can also mean angle seconds, so it is less clear
In science, the symbol s is used almost all the time, because it is clear and standard.
Current Use Around the World
The second is used in every country on Earth. It is the base time unit for:
- Everyday life, like reading clocks, timers and alarms
- Sports, for recording race and game times
- Transport, such as train and bus schedules and traffic lights
- Science and engineering, including physics, chemistry and astronomy
- Computers and phones, for files, videos and internet time stamps
- Global Positioning System GPS and other navigation systems
World time standards, such as Coordinated Universal Time UTC, are built from very accurate counts of seconds using atomic clocks in many countries.
Example Conversions
These examples show how seconds change into other time units and back.
| Seconds | Convert To | Result |
|---|---|---|
| 60 s | minutes | 1 minute |
| 120 s | minutes | 2 minutes |
| 3,600 s | hours | 1 hour |
| 86,400 s | days | 1 day |
| 1 s | milliseconds | 1,000 ms |
| 1 s | microseconds | 1,000,000 µs |
| 0.5 s | milliseconds | 500 ms |
Short rules you can remember:
- 1 minute = 60 seconds
- 1 hour = 3,600 seconds
- 1 day = 86,400 seconds
- 1 second = 1,000 milliseconds
Related Units
Other common time units that are related to the second include:
- Millisecond ms one thousandth of a second 0.001 s
- Microsecond µs one millionth of a second 0.000001 s
- Nanosecond ns one billionth of a second
- Minute min 60 seconds
- Hour h 3,600 seconds
- Day 86,400 seconds in the standard definition
- Week 7 days or 604,800 seconds
In the SI system, only the second is a base unit. The others are built from it by multiplying or dividing by numbers like 60, 3,600 or 1,000.
FAQs
Q. What is a second in very simple words
A. A second is a very short piece of time. If you count One two three in your head, each number is about one second apart.
Q. Why did scientists choose cesium to define the second
A. Cesium atoms vibrate in an extremely steady way. This makes them perfect for very accurate clocks. Using cesium keeps seconds the same length everywhere and every day.
Q. Is the second used in every country
A. Yes. The second is part of the SI system, which almost all countries follow. It is used in clocks, science and technology around the world.
Q. How many seconds are in a day
A. There are 86,400 seconds in a standard day 24 hours times 60 minutes times 60 seconds.
Q. What is faster than a second
A. Units like milliseconds, microseconds and nanoseconds are shorter than a second. For example, one millisecond is one thousandth of a second, and computers often work in these tiny time units.
Q. Can the definition of a second change in the future
A. Yes, it might. Scientists are studying even more exact atomic clocks, such as optical clocks. If they agree on a better method, the official definition could be updated, but everyday life would feel the same.