Pressure: Definition and Units
Pressure is defined as force per unit area, and its SI unit is Pascal (Pa); other common units include atmosphere, bar, and torr.
What is Pressure: Definition and Units?
The force applied perpendicular to the surface of an object per unit area over which that force is distributed.
Key formula / rule: Pressure
Key points
- Define pressure.
- State the formula for pressure.
- Identify the SI unit of pressure and its relation to force and area.
- Recognize and convert between common units of pressure.
Common exam trap
Confusing force with pressure.
Definitions
- Term
Pressure
- Meaning
The force applied perpendicular to the surface of an object per unit area over which that force is distributed.
- Term
Pascal (Pa)
- Meaning
The SI unit of pressure, defined as one Newton per square meter (1 N/m²).
- Term
Atmosphere (atm)
- Meaning
A unit of pressure approximately equal to the average atmospheric pressure at sea level.
- Term
Bar
- Meaning
A unit of pressure equal to 100,000 Pascals.
- Term
Torr (mmHg)
- Meaning
A unit of pressure equal to the pressure exerted by a column of mercury 1 millimeter high.
Learning objectives
Define pressure.
State the formula for pressure.
Identify the SI unit of pressure and its relation to force and area.
Recognize and convert between common units of pressure.
Formulae
- Name
Pressure
- Note
P is pressure, F is the perpendicular force, and A is the area over which the force is applied.
- Expression
P = F/A
Prerequisites
Force
Area
Basic Algebra
Common mistakes
Confusing force with pressure.
Not considering the area over which the force is applied.
Using inconsistent units for force and area when calculating pressure.
Keywords
Pressure
Force
Area
Pascal
Atmosphere
Bar
Torr
Fluid Mechanics
Practice preview
A force of 100 N is applied perpendicular to a surface of area 2 m². If the force is increased to 200 N and the area is decreased to 0.5 m², what is the ratio of the initial pressure to the final pressure?…
hard
If the force applied to a surface is doubled and the area of the surface is also doubled, how does the pressure change?…
medium
Which of the following is NOT a unit of pressure?…
easy