Thread: How is this possible?!

How is it possible that people/animals are able to have sufficient energy to move/consume energy all day by eating food and take enough rest?!

I figured that if we know how this works we can apply this to so much things. Even a fly can fly around all day by eating tiny bits... I know that animals/humans are very efficient, but how do we have enough energy by eating food/taking enough rest? To move something with electronics you need so much more then the calories burned by a human.

I couldn't google this, so I thought I'd ask this forum, see what results we can get!

I'm new! Hello everyone =]

Originally Posted by OnlineHobo

To move something with electronics you need so much more then the calories burned by a human.

Did you try to do the math? How many AA batteries equal the energy (a.k.a. calories) in one decent meal?

No, did you?

The efficiency of human muscle has been measured (in the context of rowing and cycling) at 18% to 26%.[15] The efficiency is defined as the ratio of mechanical work output to the total metabolic cost, as can be calculated from oxygen consumption.

http://en.wikipedia.org/wiki/Muscle#Efficiency

Dear online hobo,
welcome to the forum. You have asked an interesting question. Leszek has given you a very helpful answer. It is helpful in several ways.
1. He has pointed you towards the fact that energy contained in a meal is considerably more than that contained in a couple of batteries. (You really ought to try the calculation. You will find it very informative. If you are having difficulty then I am sure several people would be pleased to help.)
2. He has introduced you to an important part of the scientific process: that's the part where you seek to quantify what you are studying.
3. He has given you the opportunity to learn through doing, rather than through simply being told.

You seem to have misunderstood this and have responded rather rudely. Perhaps now you see the help Leszek was offering you, you will thank him.

It would take approximately 12 bananas to power a standard automobile engine for an hour, gasoline is much more cost-effective.

Originally Posted by OnlineHobo

No, did you?

No I didn't. But I'm pretty sure a good meal will be worth a lot of batteries.

Ophiolite, I'll give OnlineHobo the benefit of the doubt and assume he was not being rude - just asking if I had investigated the steak&noodles vs batteries equation and had a ready answer, which would save him some time.

Online, if you do find out, please let us know. I'm curious, but just can't afford the time to look for it myself.

Originally Posted by Leszek Luchowski

Ophiolite, I'll give OnlineHobo the benefit of the doubt and assume he was not being rude - just asking if I had investigated the steak&noodles vs batteries equation and had a ready answer, which would save him some time.

You are probably correct. Put my terse post down to jet lag and being awake at 3.00 in the morning local time.

An alkaline AA battery has a voltage of about 1.5 volts and capacity of up to 3000 milliamp-hours. That works out to 4.5 watt-hours. A watt-hour is 3600 joules, and a kilocalorie is 4.184 kilojoules, giving about 3.87 kilocalories per AA battery. It would take 98 AA batteries to equal the energy of 1 medium order of McDonald's french fries.

I couldn't resist the temptation and did the maths, very crudely, and I do not guarantee I didn't make a mistake somewhere.

My assumptions:

- the recommended daily calorie intake is a little more than 2000 "big calories" (a very confusing term used by dietitians, which means kilokalories)

- an alkaline AA battery has a charge of approx. 2700mAh at a voltage of 1.5V.

My result was that we would need something at the order of 600 batteries a day to replace the energy we get from food. That's about 1 battery every 2 minutes.

Again: this is a very careless estimation which may be totally wrong. Don't blame me if have 150 batteries for breakfast and starve to death after just 10 minutes.

PS: I notice Harold has been at it as well; his results look similar - a sixth of the number of batteries for a serving of fries that may plausibly carry a sixth of the recommended daily calorie intake.

None of the above is meant to encourage anyone to rely on fast food for their nutrition.