Pressure

In-depth explanation of Pressure

Pressure is the force acting perpendicular to a surface divided by the area over which it acts, P = F/A. The SI unit is the pascal, where 1 Pa equals 1 newton per square metre. Other common units are the atmosphere, millimetres of mercury and the bar, with 1 atm equal to 101.325 kPa, 760 mmHg or 1.013 bar. For a gas, pressure arises from the rate and force of particle collisions with the walls of the container. Because pressure depends on force per area, a sharp object concentrates a given force into a tiny area and produces a very large pressure.

Going deeper: Pressure

Key ideas: Convert units: 1 atm = 101325 Pa = 760 mmHg = 760 torr = 1.01325 bar. In a liquid column, P = rho g h, so mercury at 13.6 g/cm3 gives 760 mm for 1 atm. Gauge pressure is measured relative to the atmosphere, absolute pressure is gauge plus atmospheric. Pressure in a fluid acts equally in all directions at a given depth.

Common mistakes and connections: A classic slip is using force instead of force per area, or forgetting to convert cm2 to m2 so the answer is off by 10^4. Do not add gauge and absolute values without care. Pressure ties directly to gas laws, barometers, Dalton's law and the effect of external pressure on boiling points.

Visualization of Pressure

Pressure is force per area (1 Pa = 1 N/m2); atmospheric pressure falls with altitude, from 101.3 kPa at sea level to far less on Everest. The interactive lesson shows this as a live animation or chart.

Worked example and use case

A 60 kg person standing on one stiletto heel with a contact area of about 1 cm² exerts a pressure of roughly 6 MPa.

Where Pressure fits in States of Matter & Solutions

Pressure is topic 5 of 109 in States of Matter & Solutions.

Related topics

• Kinetic Molecular TheoryBeginner
• PlasmaBeginner
• Bose-Einstein CondensateAdvanced
• BarometerBeginner
• Standard Temperature and PressureBeginner
• Boyle's LawBeginner

Browse all 109 topics in States of Matter & Solutions