Second

What Is Second?

A second is the main unit for measuring time. It tells us how long something takes. When you count one two three while looking at a clock, each count is about one second. Seconds join together to make minutes, hours and days.

The second is one of the seven base units in the International System of Units, also called the SI system. This means many other time units are built from the second. Every digital clock, stopwatch and phone timer uses seconds in the background.

Definition

In simple words, a second is a very short, fixed piece of time that is always the same length. No matter where you are in the world, one second is equal to one second.

Today scientists use a very exact definition so that all clocks agree:

• The second is the time taken for a special type of atom called cesium 133 to make a set number of tiny natural vibrations.

You do not need to remember the big number for school use. What matters is this.

• 60 seconds make 1 minute.
• 3,600 seconds make 1 hour.
• 86,400 seconds make 1 day.

Because the second is always the same length, we can compare how fast or slow things happen, from heartbeats to space rockets.

History / Origin

The idea of the second grew slowly over thousands of years.

• Ancient times Early people watched the Sun and stars to tell time. They divided the day into big parts like morning and night but did not use seconds.
• Babylonians People in ancient Babylon liked the number 60. They split circles into 360 degrees and time into 60 parts. Long after that, people copied this and divided an hour into 60 minutes, then each minute into 60 smaller parts called seconds.
• Mechanical clocks In the Middle Ages, clockmakers built clocks with moving gears. As clocks got better, they added a seconds hand that moved step by step around the face.
• First scientific definition For a long time, one second was explained as 1 divided by 86,400 of a day, because there are 24 hours in a day, 60 minutes in an hour and 60 seconds in a minute.
• Problem with the Earth Later scientists discovered that the Earth does not spin at a perfectly steady speed. The length of a day changes a tiny bit. This made the day based second less perfect for science.
• Atomic clocks In the 20th century, atomic clocks were created. These clocks use the tiny natural vibrations inside atoms to keep time. They are much more stable than the Earths rotation.
• Modern definition In 1967, scientists agreed to define the second using the vibrations of the cesium 133 atom. Since then, atomic clocks in many countries keep world time in sync.

Thanks to this history, the second changed from a piece of the spinning Earth to a unit based on the steady behavior of atoms.

Symbol & Abbreviation

The second has a very short symbol that is used in science, school work and on devices.

• Official SI symbol s
• Common written form sec or secs in informal writing

Some tips.

• In science and on calculators, use s. Example. 10 s, 0.25 s.
• Do not add a dot after the symbol. Write 5 s, not 5 s.
• For several seconds, write 5 s in symbols or 5 seconds in words.

When you see these together.

• ms means milliseconds, or thousandths of a second.
• µs means microseconds, or millionths of a second.
• ns means nanoseconds, or billionths of a second.

Current Use Around the World

The second is used in almost every part of modern life on Earth and even in space.

• Clocks and watches Wall clocks, wristwatches, phone clocks and alarms all measure time in seconds, even when they only show minutes and hours.
• Sports and games Races, swimming, speed skating, video games and esports use seconds and fractions of a second to decide who wins.
• School and exams Timers and test schedules are written in minutes and seconds, such as a 30 second break or a 45 minute exam.
• Science and space Experiments in physics, chemistry and biology use seconds to measure how fast things change. Space missions plan rocket burns and orbits down to the second or even smaller units.
• Computers and the internet Websites load in seconds or milliseconds. Videos and music are measured in seconds. Computer programs often use timestamps in seconds.
• Medicine and health Doctors count heartbeats in beats per minute, which is based on seconds. Breathing, reaction times and medical tests also use seconds.
• Navigation and GPS GPS satellites contain atomic clocks. They send very accurate time signals in seconds so devices can find your position on Earth.

Because the second is the worldwide standard, people from different countries and languages can share time data without confusion.

Example Conversions

Here are some helpful ways to change seconds into other time units and back again.

Basic facts

• 1 minute = 60 seconds
• 1 hour = 60 minutes = 3,600 seconds
• 1 day = 24 hours = 1,440 minutes = 86,400 seconds

From seconds to larger units

• 120 seconds = 120 ÷ 60 = 2 minutes
• 300 seconds = 300 ÷ 60 = 5 minutes
• 3,600 seconds = 3,600 ÷ 3,600 = 1 hour
• 7,200 seconds = 7,200 ÷ 3,600 = 2 hours

From larger units to seconds

• 3 minutes = 3 × 60 = 180 seconds
• 10 minutes = 10 × 60 = 600 seconds
• 2 hours = 2 × 3,600 = 7,200 seconds
• 1 day = 24 × 3,600 = 86,400 seconds

Fractions of a second

• 1 second = 1,000 milliseconds (1 s = 1,000 ms)
• 1 second = 1,000,000 microseconds (1 s = 1,000,000 µs)
• 1 second = 1,000,000,000 nanoseconds (1 s = 1,000,000,000 ns)

Everyday examples

• A quick blink of your eye takes about 0.3 second.
• A normal heartbeat is about 1 beat every second or a bit faster.
• One TV or video frame is often about 0.04 second if it runs at 25 frames per second.
• A sprinter in a 100 meter race finishes in about 10 seconds.

Related Units

The second is linked to many other time units, both bigger and smaller.

Smaller than a second

• Millisecond (ms) 1 millisecond is 1 divided by 1,000 of a second. Example. 100 ms = 0.1 s.
• Microsecond (µs) 1 microsecond is 1 divided by 1,000,000 of a second. Used in electronics.
• Nanosecond (ns) 1 nanosecond is 1 divided by 1,000,000,000 of a second. Used in computer chips and very fast events.
• Picosecond, femtosecond Even smaller units used in advanced science and laser studies.

Bigger than a second

• Minute (min) 1 minute = 60 seconds.
• Hour (h) 1 hour = 60 minutes = 3,600 seconds.
• Day (d) 1 day = 24 hours = 86,400 seconds.
• Week 1 week = 7 days = 604,800 seconds.
• Year (y) About 365.25 days for an average year. That is about 31.6 million seconds.

Linked science units

• Hertz (Hz) Means events per second. For example, 50 Hz means 50 times each second.
• Speed Units like meters per second (m/s) use the second with distance to show how fast something moves.
• Acceleration Units like meters per second squared (m/s²) use the second two times to show change in speed.

FAQs

How many seconds are in 1 minute, 1 hour and 1 day

There are 60 seconds in 1 minute, 3,600 seconds in 1 hour and 86,400 seconds in 1 day.

Why is the second an SI base unit

The second is an SI base unit because many other units are built from it. Things like hertz, speed, energy and power all use seconds in their formulas, so the second must be basic and exact.

What is the correct symbol for seconds

The official SI symbol is s. In informal writing, people sometimes write sec, but in science and math you should use s.

What is a leap second

A leap second is an extra second added every few years to world time. It keeps our clocks in line with the Earths slightly uneven rotation. Some years have a minute with 61 seconds because of a leap second.

How accurate are atomic clocks that measure the second

Modern atomic clocks are extremely accurate. Some can keep time so well that they would be wrong by less than one second over many millions of years. This accuracy helps with GPS, space travel and scientific experiments.

How can I roughly feel how long a second is

You can say one thousand one out loud at a normal speed. The time it takes to say this is about one second. Many people use this method to count seconds without a clock.

What is smaller, 1 millisecond or 1 microsecond

1 microsecond is smaller. 1 millisecond is 1 divided by 1,000 of a second, while 1 microsecond is 1 divided by 1,000,000 of a second. That means 1 millisecond equals 1,000 microseconds.

Can a second ever change in length

By definition, the second does not change. Its length is fixed by the behavior of the cesium atom. What can change is how we match atomic time to the Earths time, which is why leap seconds are sometimes added.

Why do we divide time into 60 seconds and 60 minutes

This pattern comes from ancient Babylon, where people liked counting in groups of 60. This system was kept in astronomy and later in clocks, so we still use 60 based time today.

How is the second used in school science problems

In school, you will use seconds to measure speed, waves, electricity and more. For example, speed = distance divided by time. If a car travels 100 meters in 5 seconds, its speed is 20 meters per second.