# High School Physics/Si units

## Fundamental units

### Most Common Units

Meters (Distance)
Describes the space between two locations. Think of the length of a highway or the distance between two cities. The definition of the meter has changed in the last few years. The meter was originally defined as one ten millionth of the distance from one of the Earth's poles to the equator. The meter is now defined as the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second.
Kilograms (Mass)
Describes how much matter an object has. Think of the difference between a small female gymnast and large male football player. The two athletes' bodies move differently because of their difference in mass. The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.
Seconds (Time)
Describes the passage of time or aging of the universe.The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.
Kelvin (Thermodynamic temperature)
The kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
Mole (Amount of substance mole)
1. The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol."
2. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.
Ampere (Electric current)
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10^-7 newton per meter of length.
Candela (Luminous intensity)
The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

### Other Units

Potential (V)
Think about batteries (1.5v), and how you can potentially get a good trade
Temperature (K)
You won't usually see this, but otherwise think Fahrenheit when you think about the weather and think Celsius when you cook.

## Derived units

Force (N)
The Newton is a product of Mass with Acceleration, representing a force.
1.0 N = 0.24 lbs of force, defining lbs using Earth's value of gravity
Velocity (m/s)
The motion of an object based on time, with a direction. Velocity is always specified with a direction, such as “12 miles per hour north”.
If the direction is not specified, it is called Speed.
Acceleration (m/s^2)
The rate at which an object is changing Velocity.
Momentum (kg m/s)
The product of weight with speed. Note that heavy or fast objects have high momentums.

## Conversions

Though best learned in chemistry, conversion are simply ways in which you can represent a relative quantity.

Nano-10^-9 milli-10^-3 centi-10^-2 Kilo-10^3