# Dynamic Pressure

Dynamic pressure is the kinetic energy of a flowing fluid - liquid or gas - per unit volume - and can be expressed as

p_{ d }= 1/2 ρ v^{ 2 }(1)

where

p_{ d }= dynamic pressure (N/m^{ 2 }(Pa), lb_{ f }/ft^{ 2 }(psf))

ρ = density of fluid (kg/m^{ 3 }, slugs /ft^{ 3 })

v = velocity (m/s, ft/s)

### Dynamic Pressure Calculator - SI Units

The default values below are for water with density of * 1000 kg/m ^{ 3 } * .

*1 N/m*^{ 2 }= 1 Pa = 1.4504x10^{ -4 }lb_{ f }/in^{ 2 }(psi) = 0.02089 lb_{ f }/ft^{ 2 }(psf) = 1x10^{ -5 }bar = 4.03x10^{ -3 }in water = 0.336x10^{ -3 }ft water = 0.1024 mm water = 0.295x10^{ -3 }in mercury = 7.55x10^{ -3 }mm mercury = 0.1024 kp/m^{ 2 }= 0.993x10^{ -5 }atm

### Dynamic Pressure Calculator - Imperial Units

The default values below are for water with density of * 1.940 slugs * .

Some common densities at atmospheric pressure:

- Water -
*0*^{ o }C - 1000 kg/m^{ 3 } - Water -
*32*^{ o }F - 1.940 slugs/ft^{ 3 }

- Air -
*20*^{ o }C - 1.2 kg/m^{ 3 } - Air -
*60*^{ o }F - 2.373 10^{ -3 }slugs/ft^{ 3 }

### Example - The Dynamic Pressure in a Water Flow

The dynamic pressure in water with - temperature * 20 ^{ o } C * - density

*1000 kg/m*and velocity

^{ 3 }*5 m/s*- can be calculated as

p_{ d }= 1/2 (1000 kg/m^{ 3 }) (5 m/s)^{ 2 }

= 12500 Pa

= 12.5 kPa

### Example - Hurricane and Force acting on a Wall

The dynamic pressure in a hurricane with air temperature * 20 ^{ o } C, * density of air

*1.2 kg/m*and wind speed

^{ 3 }*37 m/s*can be calculated as

p_{ d }= 1/2 (1.2 kg/m^{ 3 }) (37 m/s)^{ 2 }

= 821 Pa (N/m^{ 2 })

The force acting directly on a wall with area * 10 m ^{ 2 } * can be calculated as

* F = p _{ d } A *

* = (821 N/m ^{ 2 } ) (10 m ^{ 2 } ) *

* = 8210 N *

* = 8.2 kN *

- almost the weight of a small car.

** Note! ** - the real force acting on the wall - or an other obstruction in the wind - is in general more complicated to calculate due to drag , turbulence and other effects.

## Related Topics

### • Fluid Mechanics

The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.

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