Centimetre-gram-second system of units facts for kids
The centimetre-gram-second system (often called CGS or cgs) is a way of measuring things. It's a type of metric system. This system uses the centimetre for length, the gram for mass, and the second for time. Scientists and engineers developed it in the 1800s to measure both electricity and mechanics (how things move).
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Understanding CGS Units
The CGS system has special units for things like force and energy.
Force: The Dyne
The CGS unit for force is called the dyne.
- A dyne is the amount of force needed to make a mass of one gram speed up by one centimetre every second. Imagine pushing a tiny object!
Energy: The Erg
The CGS unit for energy or work is called the erg.
- An erg is the amount of work done when you move a one-gram mass a distance of one centimetre, pushing against a force of one dyne. It's a very small amount of energy.
Pressure: The Barye
The main CGS unit for pressure is the barye (symbol Ba).
- A barye is equal to one dyne of force spread over one square centimetre.
Other units for pressure were also used with the CGS system, even though they weren't directly based on it:
- The atmosphere (atm) is a common unit. One standard atmosphere is equal to 1,013,250 baryes.
- Millimetres of mercury (mmHg) is another unit. One millimetre of mercury is about 133.32 baryes.
CGS and Electricity
The dyne and erg were also used to help define units for electrical measurements. Scientists developed two different types of CGS electrical units: one for electrostatics (about electric charges that don't move) and another for electromagnetism (about electricity and magnetism working together). However, for electrical engineering, a different system called MKS (metre-kilogram-second) became more popular.
Why CGS Changed
During the 19th and early 20th centuries, many units were created using the CGS system. But in 1960, a group called the Metre Convention introduced the International System of Units (SI). This new system was based on the metre, the kilogram, the second, and the ampere. Today, the SI system has mostly replaced the CGS system in science and everyday life because it's more widely used and easier for everyone to understand.
