Ambient pressure concept of pressure becomes irrelevant, and it is undefined at a gravitational singularity. The SI unit of pressure is the pascal (Pa), which is a very small unit relative to atmospheric pressure on Earth, so kilopascals (kPa) are more commonly used in this context. The ambient atmospheric pressure at sea level is not constant: it varies with the weather, but averages around 100 kPa. In fields such as meteorology and underwater diving, it is common to see ambient pressure expressed in bar or millibar. One bar is 100 kPa or approximately ambient pressure at sea level. Ambient pressure may in
Pascal (unit) named after Blaise Pascal, noted for his contributions to hydrodynamics and hydrostatics, and experiments with a barometer. The name pascal was adopted for the SI unit newton per square metre (N/m) by the 14th General Conference on Weights and Measures in 1971. The pascal can be expressed using SI derived units, or alternatively solely SI base units, as: where N is the newton, m is the metre, kg is the kilogram, s is the second, and J is the joule. One pascal is the pressure exerted by a force of magnitude one newton perpendicularly upon an area of one square