Fundamental Question about Dynamic Pressure.
Fundamental Question about Dynamic Pressure.
(OP)
Alright, I can't believe I need to ask this question, but I'm looking at the term in Bernoulli's equation for dynamic pressure (1/2*rho*velocity^2). Can someone explain to me the units on this this? When I look closely, it looks like it gives the answer as a unit of force, not pressure.
rho=density=kg/m^3
velocity=m/s^2
rho*velocity^2=kg/m^2*(m^2/s^2)=kg/ms^2=1 Newton!
What am I missing here?
rho=density=kg/m^3
velocity=m/s^2
rho*velocity^2=kg/m^2*(m^2/s^2)=kg/ms^2=1 Newton!
What am I missing here?





RE: Fundamental Question about Dynamic Pressure.
rho=density=kg/m^3
velocity=m/s
rho*velocity^2=kg/m^3*(m^2/s^2)=kg/ms^2=1 Newton!
RE: Fundamental Question about Dynamic Pressure.
RE: Fundamental Question about Dynamic Pressure.
RE: Fundamental Question about Dynamic Pressure.
RE: Fundamental Question about Dynamic Pressure.
To PhilipFry,
As BronYrAur says 1 kg/(ms2) is a pressure unit = 1 Pascal = 1 Pa = 1 N/m2. And as blackwed rightly says the unit of force (=mass×acceleration) 1 N = kg.m/s2.
When ρV2/2 (kinetic energy per unit mass of the Bernoulli equation) is divided by ρg, it results in V2/2g, and we obtain velocity head, with dimensions of length, m.
RE: Fundamental Question about Dynamic Pressure.
Force is either expressed in Newtons or Kgf
Pressure is either expressed in Newtons/m2 or kgf/m2
What you got is a simplified unit and is kgm/(m.s2) and here kgm is kg mass (later on I will just use kg for kg mass).
Multiply and divide this with meters and you will get
kg x m/ (m x m x s2) = kg x m/(m2 x s2)
by rearranging the terms,
(kg x m/s2)x(1/m2) = N/m2, which is a pressure unit.
Fluid mechanics text books, use a constant gc when dealing with FPS system of units and express the dynamic head as rho*v2/2gc. Here, gc is 32.17 ft.lbm/lbf.sec2
This constant is not required for metric system as Newton is directly expressed as kg.m/sec2. However, you can derive the pressure units for dynamic head by using the constant gc with units kg.m/N.sec2
RE: Fundamental Question about Dynamic Pressure.