Energy measurment?

[Brycesv1]

was eating at good ol' McDonalds and a thought came to me. could you measure something like rocket fuel in calories? a calorie is just the amoutn of energy it takes to heat 1 milliletre of water 1 degree celcius (i think) so couldnt u measure the energy content of anything else with calories?

 

[Linguofreak]

Yes, you could. Rocket scientists tend to be stuck on SI, though, and use joules. (Also, I'm doing an exchange year in Germany at the moment, and all the food in my cupboard has its energy content listed in kilojoules, not Calories).

Also, you have to be careful with the spelling of the words calorie and Calorie.

"calorie", with a small c, is as you have said, the amount of energy required to raise the temperature of one gram of water by one degree (the gram was originally defined as the mass of one milliliter of water at 0 C).

"Calorie" with a big C is the unit used for measuring the energy content of food, and is equal to the amount of energy required to raise the temperature of one *kilogram* of water by one degree, or 1000 small-c calories.

It's confusing, I know.

But you can measure the energy content of anything in any unit of energy you wish: The Calorie, the calorie, the joule, the gram*c^2, the electron volt, the erg, the firkin*(furlong/fortnight)^2, the horsepower-nanoparsec/c, the gigaparsec*atomic-mass-unit-force, or the megaton TNT equivalent.

 

[tblaxland]

[...]the firkin*(furlong/fortnight)^2[...]

I'm curious how the 90 lb firkin used by the FFF system came to be, especially since it is not mentioned on the firkin wikipedia entry. Its sounds like it is an approximation of the mass of water contained in a beer firkin.

 

[the.punk]

Yes. It's just another energy measurment.

1 Calorie (kilocalorie) = 4184 joules

1 calorie = 4.184 joules

EDIT: Linguofreak: But as far as I know we have also kcal for food.

 

[Arthur Dent]

(Also, I'm doing an exchange year in Germany at the moment, and all the food in my cupboard has its energy content listed in kilojoules, not Calories).

Most food is labeled with kilojoules. But you can find calories on our food packaging. To be more precise: kilo-calories (C). We abbreviate it kcal.

 

[tblaxland]

Most food is labeled with kilojoules. But you can find calories on our food packaging. To be more precise: kilo-calories (C). We abbreviate it kcal.

Our food here used to have both, but is trending towards just having kJ. This led someone I know, who was just starting a diet, to exclaim "Wow, this great, these crumpets have no calories!" :lol:

 

[the.punk]

Most food is labeled with kilojoules. But you can find calories on our food packaging. To be more precise: kilo-calories (C). We abbreviate it kcal.

I think sometimes we have also both.
kJ and kcal on food.

 

[Linguofreak]

I'm curious how the 90 lb firkin used by the FFF system came to be, especially since it is not mentioned on the firkin wikipedia entry. Its sounds like it is an approximation of the mass of water contained in a beer firkin.

Footnote 2 to the FFF system article says:

The firkin of the FFF System is defined as the mass of an imperial firkin (9 imp gal) of water. The imperial gallon was originally defined as the volume of 10 lb of distilled water (weighed according to specific conditions). From this definition a density of 10 lb/imp gal is derived, giving the firkin of water a mass of 90 lb.

 

[Urwumpe]

You can also measure the power of a rocket engine... it is just P = F * w, the product of thrust and exhaust velocity/specific impulse. Of course you quickly end in unbelievable Gigawatts that way, but that is the truth - a single SSME produces as much power per second as a small nuclear power plant. But the nuclear power plant does so 24/7, the SSME just for 5x8 minutes.

 

[Brycesv1]

interesting... now im starting to wonder how much horse power my cheeseburger has...

 

[Andy44]

interesting... now im starting to wonder how much horse power my cheeseburger has...

Well, if it's from McDonald's, it might be a quarter-pund of 1 horsepower.

 

[thomasantony]

interesting... now im starting to wonder how much horse power my cheeseburger has...

Well that would be like asking how much horsepower a liter of petrol has. It doesn't make sense.

It would depend on how fast you burn the cheeseburger, or what process you use to extract energy from the cheeseburger. Would also depend on the engine that does it I guess.

 

[Brycesv1]

*stuffs cheeseburger into Mazda RX8 gas tank*

 

[the.punk]

Well that would be like asking how much horsepower a liter of petrol has. It doesn't make sense.

It would depend on how fast you burn the cheeseburger, or what process you use to extract energy from the cheeseburger. Would also depend on the engine that does it I guess.

You're right. Horsepower isn't an measurment for energy. It's for power.
Power is energy per time.

 

[RisingFury]

So, if anyone's up for a calculator challenge...

How much energy did a Saturn V rocket have at liftoff in electron-volts?

 

[Linguofreak]

interesting... now im starting to wonder how much horse power my cheeseburger has...

Depends how fast you eat it. :lol:

Power is energy per unit time. 1 horsepower is .178 Calories per second.

Of course, technically power is the rate at which you burn those calories, not the rate at which you eat them (since the energy is just sitting there in the food as the food goes down your throat, not doing anything or going anywhere itself).

A 2500 Calorie/day diet is a .16 horsepower diet.

---------- Post added at 03:33 PM ---------- Previous post was at 03:00 PM ----------

So, if anyone's up for a calculator challenge...

How much energy did a Saturn V rocket have at liftoff in electron-volts?

Stored in the fuel you mean?

Or did you mean how much power does it put out in electron volts per unit time?

For power, the average output of the first stage was 190 gigawatts, which comes to about 1.2 tera-electron-volts / attosecond.

As for total energy stored in fuel, that's a bit more complicated, cause I'm having a hard time finding figures for the energy content of the fuel, and it uses umpteen fuels (Kerosene/LOX for the first stage, LH2/LOX for the second and third, I don't know what for the RCS, and then whatever the payload has). But after you find all that, you can just find the total mass of each fuel type used and multiply by its energy content. Then multiply joules by 6.24 * 10^18 to get electron volts.

 

[the.punk]

So, if anyone's up for a calculator challenge...

How much energy did a Saturn V rocket have at liftoff in electron-volts?

Yes.
The question must be a little bit different because Power is energy per time.
As Linguofreak calculated.

For the energy content of the fuel you must know the mass of fuel and the power and the time it takes to burn the whole fuel.

 

[RisingFury]

No no, I meant energy stored in fuel. Gotta be some awfully big number once you put it into eVs.

 

[the.punk]

No no, I meant energy stored in fuel. Gotta be some awfully big number once you put it into eVs.

Ok. Then you need as I said the mass of fuel, the power of engine and the time it takes to burn the fuel.
hmm...

Power: 190 Gigawatts
Time: 161 Sec

P = E / t
....
E = P * t

E= 190 Gw * 161 = 30590 GWs = 30590 GJoule = 3.059 * 10^13 joules

3.059 * 10^13 joules * 6.24 * 10^18 =

Energy content of first stage............

Right?

 

[Linguofreak]

Of course, another way of interpreting the question might be "How much mass-energy did the Saturn V have at liftoff in eV" (eV are generally used in particle physics, where they are used to measure the combined rest mass and kinetic energy of particles (since velocities are often relativistic, and the kinetic energies involved can be a good deal greater than the rest masses of the particles).

Then we're talking 1.7 * 10^30 TeV.