Stuck on a Water Tower Pressure Problem: Dynamic or Static?

[Idea04]

i'm stuck on a problem. Let's say you have a large water tower. and the pressure is basically static pressure from the weight of the water. But when the water starts moving through pipes is the pressure then dynamic pressure? In which would you have to calculate the pressure from 1/2 density of water times velocity ^2.

And another thing, I was studying hydraulic multiplication briefly. What I studied was you have a 2 inch diameter piston moving nine inches downward with a hundred pounds force. And it pushes a 6 inch diameter piston upward 1 inch with 900 pounds force. My question is if you pushed down the large piston with a hundred pounds force, then what kind of force will the small piston get.

 

[Andrew Mason]

i'm stuck on a problem. Let's say you have a large water tower. and the pressure is basically static pressure from the weight of the water. But when the water starts moving through pipes is the pressure then dynamic pressure? In which would you have to calculate the pressure from 1/2 density of water times velocity ^2.

Bernoulli's principle applies. Pressure is a measure of the energy density of the fluid. Pressure can be converted to kinetic energy density (KE/unit volume), in which case the pressure must decrease by the amount of the increase in kinetic energy density.

And another thing, I was studying hydraulic multiplication briefly. What I studied was you have a 2 inch diameter piston moving nine inches downward with a hundred pounds force. And it pushes a 6 inch diameter piston upward 1 inch with 900 pounds force. My question is if you pushed down the large piston with a hundred pounds force, then what kind of force will the small piston get.

I think you can figure that out. Put a 900 lb downward force on the large piston. and a 100 lb downward force on the small piston. Does either piston move? What is the force being exerted by the large piston, then, on the small one? What is the force exerted by the small on the large?

AM

 

[kyle8921]

I would first like to clarify the difference between dynamic and static pressure. Static pressure is the pressure exerted by a fluid when it is not in motion, while dynamic pressure is the pressure exerted by a fluid when it is in motion. In the case of a water tower, the pressure at the bottom of the tower would be considered static pressure as it is solely due to the weight of the water above it. Once the water starts moving through pipes, the pressure would become dynamic as the water is now in motion.

To calculate the dynamic pressure, you would indeed use the formula 1/2 density of water times velocity^2. This is because the velocity of the water is what causes the pressure to change.

Regarding the hydraulic multiplication problem, it is important to note that the force exerted by a fluid is equal to its pressure multiplied by its area. In this case, the force exerted by the smaller piston would be 900 pounds, as it has a larger surface area and therefore experiences a greater pressure from the fluid. This is known as the principle of Pascal's law, which states that pressure applied to a fluid in a closed container is transmitted equally to all parts of the container.

I hope this helps in understanding the concepts of static and dynamic pressure, as well as the principle of hydraulic multiplication. If you have any further questions or difficulties with the problem, please feel free to ask for clarification.