Bernoulli's equation explanation

[shanewatson]

In Bernoulli's equation, why the work on fluid at the lower end of the pipe is taken as negative?
please explain why the force is negative to displacement at the lower end?

 

[sankalpmittal]

In Bernoulli's equation, why the work on fluid at the lower end of the pipe is taken as negative?
please explain why the force is negative to displacement at the lower end?

Just a sign convention. Assume it the opposite : Lower end positive and upper end negative... The result will remain unchanged provided you keep on using the sign convention throughout the derivation.

 

[rcgldr]

please explain why the force is negative to displacement at the lower end?

The convention is to consider upwards movment and upwards forces as positive, and downwards movement and downwards forces as negative. Gravitational potential energy is the negative of the work done by gravity, so GPE increases (more positive or less negative) as an object moves upwards, and decreases as an object moves downwards. The potential term in Bernoulli's equation follows the same rule, but it's potential energy per unit volume (density x gravitational acceleration x height).