1. May 8, 2009

### vivekfan

1. The problem statement, all variables and given/known data
1. Is pressure always force/area? or is it only for static fluids?
2. I read that the equation for hydrostatic pressure is (initial pressure) + density x gravity x height, but How would I know to use that instead of Force/Area? Also is the initial pressure always atmospheric?
Why in bernoulli's equation is it just pressure and not using the quantity (density x volume x height?)

2. Relevant equations
I have stated relevent equations above.

3. The attempt at a solution

I just keep getting confused with concept and would appreciate some help. Thanks
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited: May 8, 2009
2. May 8, 2009

### minger

oh boy. What class is this for, and what have you learned so far?

1. Is pressure always force/area? or is it only for static fluids?
Pressure is force divided by an area. It exists in static fluids, moving fluids, everywhere.

2. I read that the equation for hydrostatic pressure is (initial pressure) + density x gravity x height, but How would I know to use that instead of Force/Area? Also is the initial pressure always atmospheric?
Pressure is BOTH. If the hydrostatic pressure of water at 100 meters is:
$$p = p_\infty + \rho g h = 101.3 kPa + (1000 kg/m^3)(9.81 m/s^2)(100m) = 1082 kPa$$
Then that means that the fluid will exert 1082 N of force for every 1 meter of area.

3. Please help describe pressure for moving fluids? Why in bernoulli's equation is it just pressure and not using the quantity (density x volume x height?)
Bernoulli's equation is a form of conservation of energy. It basically says that energy cannot be created or destroyed, only transferred. In laymens' terms, it says that the internal energy (pressure) plus kinetic energy (velocity) plus potential energy (height) stays the same.

3. May 8, 2009

### vivekfan

Could you explain Pascal's principle? What is an incompressible fluid and how is a change in pressure applied to an incompressible fluid independent of height?