# effect of area on the pressure of a liquid

• March 4th, 2008, 07:55 PM
organic god
effect of area on the pressure of a liquid
was in a lesson and the teacher gave this talk which i was following until the end.

If a fluid flows in a pipe which has one point of entry and one point of exit the mass flow rate in = mass flow rate out.
due to law of conservation of mass. therefore we get the following equation

p(1)A(1)v(1) = p(2)A(2)v(2)

because liquids are incompressible the density is constant whatever the pressure therefore

A(1)v(1) = A(2)v(2)

fluid travels fastest through the narrowest sections.
therefore indicating individual particles accelerate.

according to Newtons second law, the forces on the particles must therefore be unbalanced.

This implies the pressure is lowest at the narrowest points

i don't understand how he derived the part in bold. can someone explain how this link was made, thanks
• March 4th, 2008, 08:11 PM
Bunbury
It's a statement of the principle of energy conservation. See the wiki entry on Bernouilli's principle.

http://en.wikipedia.org/wiki/Bernoulli's_equation