Food pressure

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Food pressure

Postby heatsink » Wed Feb 17, 2016 6:53 am UTC

Today, Google calculator taught me that energy density has the same units as pressure. Weird! Force per area = energy per volume, but why? For an ideal gas in a rigid container, the kinetic energy per volume can indeed be translated into stuff-per-area. Using the velocity distribution at a given pressure, you can find the momentum flux. That's the momentum per time flowing in one direction through any area in the gas, not counting the opposing flow that balances it. Momentum per time is force, so the momentum flux is the pressure that the gas exerts on the container.

The fun part is that this equivalence can be abused. The amount of calories in a cup of food is also an energy density. Food has a pressure! With 55 food calories per cup, cantaloupe contains approximately one gigapascal.

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Re: Food pressure

Postby Sizik » Wed Feb 17, 2016 4:20 pm UTC

Wikipedia says the following:
Energy Density wrote:Energy per unit volume has the same physical units as pressure, and in many circumstances is a synonym: for example, the energy density of a magnetic field may be expressed as (and behaves as) a physical pressure, and the energy required to compress a compressed gas a little more may be determined by multiplying the difference between the gas pressure and the external pressure by the change in volume. In short, pressure is a measure of the enthalpy per unit volume of a system. A pressure gradient has a potential to perform work on the surroundings by converting enthalpy until equilibrium is reached.
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Re: Food pressure

Postby LucasBrown » Wed Feb 24, 2016 2:03 am UTC

Soooo.... convert the chemical potential energy of that cantaloupe into heat but keep it in the same volume, and you'd have a gas with 109 Pa of pressure?

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Re: Food pressure

Postby ijuin » Wed Feb 24, 2016 3:10 am UTC

Assuming ideal gas laws (gas molecules as pointlike objects with infinite compressibility, all momentum is 100% linear and zero% rotational, etc.), then yes.

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