pascal
Summary Four quantities must be known for a complete physical description of a sample of a gas: temperature, volume, amount, and pressure. Pressure is force per unit area of surface; the SI unit for pressure is the pascal Pa , defined as 1 newton per square meter N/m2 . The pressure exerted by an object is proportional to the force it exerts and inversely proportional to the area on which the force is exerted. The pressure exerted by Earths atmosphere, called atmospheric pressure, is about 101 kPa or 14.7 lb/in.2 at sea level. Atmospheric pressure can be measured with abarometer, a closed, inverted tube filled with mercury. The height of the mercury column is proportional to atmospheric pressure, which is often reported in units ofmillimeters of mercury mmHg , also called torr. Standard atmospheric pressure, the pressure required to support a column of mercury 760 mm tall, is yet.