(N) The SI unit of force.
Definition: 1 newton will accelerate a mass of 1 kilogram at the rate of 1 meter per second.
The relationship between force (F), mass (m), and acceleration (a) is expressed by the formula: F = ma.
The newton is named for Isaac Newton (1642-1727), the British mathematician, physicist, and natural philosopher.

(Osm) A unit of osmotic pressure used in physical chemistry, cell biology, and medicine.
Definition: 1 osmole is the osmotic pressure of a one molar solution (that is, a solution with a concentration of one mole per liter of solvent) of a substance that does not dissociate.
If chemical solutions are separated by a semipermeable membrane (a membrane that resists the passage of dissolved substances but permits the passage of the solvent, usually water), then the solvent will diffuse across the membrane to equalize the concentrations. This process is called osmosis.
Solutions with higher concentrations of dissolved substances are said to have higher osmotic pressure than solutions having lower concentrations; thus the solvent moves from an area of low osmotic pressure to an area of higher osmotic pressure.
Osmotic pressure depends on the total number of dissolved particles, so for a substance that dissociates into two ions, such as ordinary salt (sodium chloride), a one molar solution has an osmotic pressure of 2 osmoles. In practice, most measurements are in milliosmoles (mOsm). Typical values range from 20 mOsm for fresh water through 290 mOsm for typical human blood plasma to 1010 mOsm for salt water from the open ocean.
See also Part Per Million.

(ppm) Part per million is a unit of proportion equal to 10^-6.

(Pa) The SI unit of pressure.
Definition: 1 Pascal is equal to 1 N/m² = 1 J/m³ = 1 kg x m^-1x s^-2
1 kPa = 0.145 lbf/in².
Air pressure is measured in hectoPascal (hPa), with 1 hPa = 1 millibar.
The unit is named for Blaise Pascal (1623-1662), French philosopher and mathematician.

A logarithmic measure of sound loudness closely related to the decibel. The unit decibel is used for objective measurements that mean, they measure the actual pressure of the sound waves as recorded using a microphone. The unit phon is used for subjective measurements, which means, measurements made using the ears of a human listener.
A sound has the loudness 'p' phon if it seems to the listener to be equal in loudness to the sound of a pure tone of the frequency 1 kilohertz and strength 'p' decibel. A measurement in phons will be similar to a measurement in decibels, but not identical, since the perceived loudness of a sound depends on the distribution of frequencies in the sound as well as the pressure of the sound waves. In the U.S., sound loudness is frequently measured in sones rather than phons: a sound of loudness x sones has loudness 10 log2 x + 40 phons.

(rad) One rad is the absorbed radiation dose of 100 ergs of energy by one gram or 0.01 joules of energy by one kilogram of matter. In the SI system of units, the rad is replaced by the gray (Gy). 1 Gy = 100 rad. See also Absorbed Dose Rate.