# Bernoulli's equation derivation

1. Sep 18, 2011

### logearav

1. The problem statement, all variables and given/known data

In bernoulli's equation derivation, we use Work energy theorem, in which work done is taken as change in kinetic energy plus change in potential energy.
But in mechanics, i have studied, Work energy theorem is simply change in kinetic energy.
So, which is correct? Pls help revered members

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Sep 18, 2011

### ehild

The work Energy Theorem states that the change of KE is equal to the work of all forces. If one of the forces is conservative, the work of that force is equal to the negative potential energy change. If you have two forces, Fa and Fb, and Fb is conservative, with PE(b) potential energy,

ΔKE=W(a)+W(b)=W(a) -ΔPE(b), that is W(a)= ΔKE+ΔPE(b)

When deriving Bernoulli's equation, one force comes from the pressure at the cross-sections of the tube containing the fluid. The other force is gravity.

ehild

3. Sep 18, 2011

### logearav

Thanks Mr.ehild for your beautiful explanation.