A cup of black coffee (capacity 0,25 L) lies a rather considerable energy. I do not think that I mean the miracle chemical composition of coffee, thanks to which a cup of hot beverage is able to put on your feet tired man. A large amount of energy contained in a 0.25 liter of hot water.
Do not believe me? I will try to prove it to you. You know that the specific heat of water is 1 cal / g. Multiplying 250 by 80 (assuming that t coffee - 80 ° C), we get 20,000 calories, or 20 kcal, ie such warmth or energy has a cup of coffee.
"A 20 kcal a lot or a little?" - Probably, you ask.
Let's compare this thermal energy to other forms of energy.
Take for example the most charged battery voltage of 2 V and a capacity of 12 Ah. and fully discharge it. He can give us 2 • 12 = 24 watt-hour or 86,400 watt-seconds (1 watt-seconds - 1 J). It is known that 1000 watt-seconds - is 0.24 kcal, while 86,400-volt seconds are equal to 20 kcal.Thus, a hot cup of coffee contains as much energy as the charged battery voltage 2. The same energy bulb consumes 25 W, burning for an hour.
Now replace kilocalories units of mechanical energy. Since 1 kcal corresponds to 427 kg-m, 20 kcal equivalent 8500 kg-m. On each shot, a heavy hammer blacksmith consumes energy about 20 kg-m. So the energy contained in a cup of coffee, it will be enough for more than 400 blows with a hammer.
Finally, the last comparison. 20 calories - the energy which has a powerful five-ton hammer falling from a height of 1.75 m.
That is, what is equivalent to the energy enclosed in a normal cup of coffee!
S. Senkovsky