# B Question regarding pressure and energy

1. May 10, 2018

### GabrielLight

I'm referring to pressure as in atm, pascals and PSI, and energy as in joules or watts.

Can pressure be converted to energy in some way? I'm aware of the existence of "pressure energy", which is joules per volume, but it's not what I mean.

For example, if a pressure of 100,000 atm is exerted on a man with a surface area of 1.8m², could we somehow translate the pressure to watts/m², without violating fluid dynamics? Or are pressure and energy not related in this form?

2. May 11, 2018

### haruspex

Pressure and energy are dimensionally different, so there is certainly no conversion from one to the other.
(You mention Watts, but that is a unit of power, which is different again.)
To get an energy from a pressure you need, in effect, a volume to multiply it by. That arises directly in the gas laws, e.g. pV constant at constant temperature. In Bernoulli's equation for incompressible flow we also find a p/ρ term, which we can think of as an energy per unit mass which somehow results from the pressure, p.

Can you explain more why you ask, or why you feel it should be possible?

3. May 14, 2018

### Lukeblackhill

If you apply a force in a body of volume V, in its area surface A, the body experiences a pressure P=F.A that acts in it in order to peform one or more of this actions, such as a. expanding, b.contracting, c. deforming, d.heating, etc. In all cases, the P.V = W, that is the work done on the body. Knowing that W = K - Ko, you can see this relation. The pressure of a certain volume hot steam in a piston is the source of generating kinetic motion...you can also use the steam to rotate the stems of a mill, etc.

4. May 14, 2018

### Staff: Mentor

I'm surprised this didn't get a more direct response:

Pressure has units of energy per unit volume and can be thought of in that way. But Watts are power, not energy. Energy is static, whereas power is rate of energy generation. So no, you can't take a static form of energy and have it continuously output power. It needs to be changing.

5. May 14, 2018

### Staff: Mentor

Actually, pressure has units of energy per unit volume, which makes it useful in situations such as Bernoulli's equation.

6. May 14, 2018

### haruspex

Not quite. The work done is P.dV, i.e. there has to be a change in volume.
I did point that out in post #2.
That does not contradict what I wrote. It still leaves pressure and energy dimensionally different, just as energy and power are dimensionally different. In the one case the ratio is a volume, in other, time.

The OP explicitly stated that a direct conversion was sought, not pressure as energy per volume.