Bernoulli's Eq: P1=P2 & Torricelli's Eq

[bluejay27]

When using Bernoulli's equation to describe fluid that is coming out from a spigot, why is it that P1 = P2 are the same? This cancellation will eventually lead to the Torricelli's equation.

 

[Doc Al]

In deriving Torricelli's theorem, both ends of the streamline are assumed to be at atmospheric pressure. (They are exposed to the atmosphere.)

 

[bluejay27]

Isn't the pressure supposed to be internal pressure?

 

[Doc Al]

Isn't the pressure supposed to be internal pressure?

Yes, it's the pressure inside the fluid. At those points that pressure must match the external atmospheric pressure.