Fluids mechanics is also gas mechanics?

[Studiot]

It is not fashionable to teach basic mechanics quantities these days but here are some that are applicable to this hydraulic lift and other purely mechanical things like levers and pulleys.

$${\rm{VelocityRatio = VR = }}\frac{{{\rm{distance}}\,{\rm{moved}}\,{\rm{byload}}}}{{{\rm{distance}}\,{\rm{moved}}\,{\rm{byeffort}}}}$$

$${\rm{MechanicalAdvantge = MA = }}\frac{{{\rm{load}}}}{{\,{\rm{effort}}}}$$

$${\rm{Efficiency = }}\frac{{{\rm{MA}}}}{{{\rm{VR}}}}$$

and finally what is really the law of conservation of energy

$${\rm{load*distance}}\,{\rm{moved}}\,{\rm{by load = effort*distance}}\,{\rm{moved}}\,{\rm{by}}\,{\rm{effort}}$$

Which you can see equals MA * VR

 

[I like Serena]

Similarly, it can sometimes be assumed that the viscosity of the fluid is zero (the fluid is inviscid). Gases can often be assumed to be inviscid. If a fluid is viscous, and its flow contained in some way (e.g. in a pipe), then the flow at the boundary must have zero velocity

This is because the fluid sticks to the walls, right?

Perhaps a bit late, but I'd like to answer this question anyway.

I'll stick my neck out and say: yes, it is because the fluid sticks to the walls.
Or rather, the friction between the fluid and the wall makes it stand still where it makes contact with the wall (in modelling).