Second (disambiguation) facts for kids

A "second" is a very important word with several meanings! Most often, it's known as a small unit of time. It's also used to describe something that comes after the first, like the number two.

What is a Second?

A second is the basic unit of time in the International System of Units (SI). We use seconds to measure how long events last. There are 60 seconds in one minute, and 60 minutes in one hour. This means there are 3,600 seconds in an hour!

For a long time, a second was defined based on the Earth's rotation. However, the Earth's spin can change slightly. Because of this, scientists needed a more exact way to define a second.

How We Measure Seconds

Today, a second is defined using very precise atomic clocks. These clocks measure the vibrations of atoms, specifically cesium atoms. One second is the time it takes for a cesium-133 atom to vibrate exactly 9,192,631,770 times. This makes the second one of the most accurately measured units in science!

Atomic clocks are incredibly accurate. They are used for many important things. For example, they help make sure GPS systems work correctly. They also help keep computer networks around the world in sync.

Other Meanings of "Second"

The word "second" has other uses too, depending on what you are talking about.

Second as a Number

When you count, "second" means the item that comes after the first one. For example, if you finish a race after the winner, you are in "second place." The number two is the second positive whole number.

Second in Music

In music, a "second" describes the distance between two notes. It's a musical interval. For example, if you play a C note and then the D note right after it, that's a "major second." There are different types of seconds in music, like:

• Minor second: This is the smallest distance between two notes in Western music, also called a semitone.
• Major second: This is a whole step between two notes.
• Diminished second: This is when two notes are played at the same pitch, also called a unison.

Second in Other Areas

• Arcsecond: This is a tiny unit used to measure angles, especially in astronomy. It's a very small part of a degree.
• Second of right ascension: In astronomy, this helps locate objects in the sky, similar to how longitude works on Earth.
• Second (parliamentary procedure): In meetings, when someone "seconds" a proposal, it means they agree with it and want it to be discussed.
• Second in sports: In sports like boxing, a "second" or "cornerman" is someone who helps a fighter during a match. They give advice and support between rounds.