If the Human body ran on electricity, how many watts would it consume per day?
If we assume the electricity->energy conversion is as efficient as food->energy, you need the equivalent of about 3000 Calories per day. That’s 12,000,000 Joules per day. If you’re hooked up to the wire 24 hours a day, average power is 145 Watt.
According to this calculator, at an average daily metabolism of 2000 kilocalories, the human body produces 2.32444 kilowatt hours per day.
First a watt is a unit of power. So it does not make sense to ask watts per day.
1 calorie = 4.2 joules
About 2500 Kcalories is a decent guess for the amount of energy people use in a day. So that is 1.05 * 10^7 J.
Which averaged over a day is 121.5 W.
So that is about 2.917 KWatt hours. In a day
Am I correct in assuming that is remarkably efficient?
You’re running a hydraulic system with a pump 24/7, periodic use of other various servo-motors with a lifting capacity of many kilograms, a heating system, as well as a very fast computer with multiple peripherals. All this for the same energy as a couple light bulbs? That seems quite good.
I’ve typically heard 100 W. Judging by the calculations already posted, it seems that this would be based on a requirement of 2000 calories per day, or maybe less. Keep in mind, though, that the calorie as a unit of the energy content of foods is determined primarily by burning those foods, and indicates how much chemical energy they contain but not how much energy the body can get out of them. Varying levels of availability (digestion and absorption), as well as the basic inefficiency of cellular respiration, will make the actual energy requirement substantially smaller than the total energy available in food. (But scr4 has already qualified this by assuming that the electricity-to-energy conversion is as efficient as the food-to-energy conversion.)
TheLoadedDog: This source (which cites my molecular biology textbook) says the conversion of glucose (i.e. carbohydrates) to energy is 38% efficient in vitro and ~50% efficient in cells. It also says this is substantially more efficient than an electric or gasoline motor, which waste much of their energy as heat. Some systems show remarkable efficiency. A neuron, for example, operates with a voltage of about 70 mV; a microprocessor requires ~3000 mV (3 V) at the very least. In muscle, useful work is being done by the whole muscle, and each cell is largely taken up by fibers that do this work.
Running a heating system, though, is a byproduct of running any sort of system. The temperature of the human body is maintained by the wasted energy of metabolism, just as the temperature of a gasoline engine is maintained by the wasted energy of combustion. When this is not sufficient, there are proteins that do nothing but hydrolyze ATP to produce heat.
A friend who worked in a calibration lab with a lot of very sensitive equipment told me that they had a bank of 100W incandescent light bulbs, one for each member of the staff. When you entered the lab, you turned off your light bulb. When you left the lab, you turned on your light bulb. They were trying to maintain a constant temperature in the lab, and had figured out that the typical staff member produced 100W of heat.
Clever, but wouldn’t it be simpler to use a highly accurate thermostat? Or do thermostats not go that accurate?
I used to work as furnace and airconditiong operator at a theater. On nights when a large crowd was anticipated the theater had to be about 3-4 deg cooler than on light nights because the large crowd heated it up quite a bit.
You raised a question similar to one I’ve had for a while. If one looks at the actual work in foot lbs that a calorie represents, it appears that lifting 1foot ~3feet would burn 1 calorie. This means that doing 10 repetitions of lifting 100lbs 3feet would burn 1000 calories. This could be done in a matter of a few minutes. And yet the calorie burn reported by exercise equipment is much less than this.
Is it possible that the energy our body gets from food is alot more than the calorie value one gets via the calorometer (burning) method, via chemical reactions, or from the atomic level?
Jethro, You confusing calories and Kilo calories in your calculation, always a problem. 1 calorie is ~3 foot pounds. 1 calorie when talking about food or exercise is really ~3000 foot pounds.
I think you’re confusing the measure “calorie” with the measure “Calorie” that we use in reference to food. A “Calorie” is really a kilo-calorie, or 1000 small calories.
Darn. Calorie no longer looks like a real word. :eek:
Yes indeed.
If the lab was truly serious and had the budget, they could very tightly control that environment. I have experienced this in automotive emissions R&D filter labs. Basically, filters are weighed on very sensitive scales*, then dropped into the exhaust path to catch particulates, then weighed again to measure those particulates. The filters will soak up humidity and potentially introduce static electric charges and temperature convections to the weighing environment so they must be conditioned under very strict specifications to make sure that they are only weighing those emissions. Even then, there’s a heavy application of statistical analysis to identify and weed out false reads and errors.
Anyway, the lab is double airlocked with constant realtime temp, humidity, dew point and vibration (maybe others) monitored. It is pretty serious business. Light bulbs wouldn’t even get you close unless they were modulated via thermostats.
*2.1 x 0.0000001 grams is typical.
My best guess is that you’re confusing “calories” with “Calories”; that is, confusing the “calories” that a physicist uses with the “Calories” that a nutritionist uses. When the word is not capitalized, it refers to a particular unit of energy. When it is capitalized, it is a different unit of energy 1000 times greater. Often people will refer to “Calories” as “kilocalories” to note the difference.
EDIT: And I’m late.
Not to mention an incredibly precise audio/visual system, all in a package constructed entire out of organic material!
A funny story re cals and Kcals… A guy wrote a scientific paper, and “proved” that draft animals were more efficient for ploughing fields than tractors were. He was using Kcals for the fodder for the animals, but cals for the energy in gasoline/diesel engines. Oops…
Trinopus (BTU anyone?)
How many watts does a zombie consume?
That’s an interesting question. Assuming actual undead zombies (rather than living rabid pseudo-zombies), you have no cardiovascular system, no digestive system, and reduced brain functions, which means a significantly lower calorie output.
I guess it depends on the zombie’s level of activity. A zombie waiting by a cursed tomb probably expends little to no energy; a zombie stalking you through a shopping mall burns more, but less than a living human moving at the same speed.
But brains are high calorie, having a high fat content. As we have learned, calories burned must equal or exceed calories consumed, else we would see a lot more fat zombies. They always look pretty gaunt to me, so I’m guessing chasing victims is pretty aerobic, to keep them so trim in spite of their diet.
But bear in mind that it usually takes a horde of zombies to hunt down a single group of survivors - meaning that on average, dozens, if not hundreds of zombies have to share each brain. Even if a lucky zombie gets to consume an entire brian by itself, it might have to wait for weeks, if not months until it finds a new one. Those brain calories have to last awhile.