Half a litre of water has a mass of 0.5Kg (at 4°C).

Let's assume we're going to boil water that's initially at 20°C, and let's further assume that the mass difference at this temperature is negligible.

So we want to raise the temperature of 0.5Kg of water by 80°C, which needs this much energy:

Energy required = 4.816J * 500g * 80°C Bollocks - typo (pointed out by Bruce)

Energy required = 4.186J * 500g * 80°C

= 192,640 167,440 J

Gravitational potential energy E (in Joules) of a mass = mgh, so to get enough to boil your half litre of water (and assuming a 100% efficient conversion of this PE) you need to drop your 1 tonne weight from a height of:

h = E/mg = 192,640J / (1000Kg * 9.81 m/sec²)

h = E/mg = 167,440J / (1000Kg * 9.81 m/sec²)

= 17.07m

Numerologists please note that this is the same height in metres as the number of Joules needed to boil water from 20°C, if you remove the digits '2' and '0' from 192640 J and then divide the result by 100 (the boiling point of water in °C).

Numerologists should further note that 1964 is the year I was born.

Numerologists should sod right off!
--
simon

Note how I deliberately took the erroneous value of "1" to be the number of joules required to raise the temperature of 1cc (gram, effectively) of water by 1 degree centigrade.

I also assumed 20 degree start point and before my 80% efficiency calculation had as near as dammit 4 metres. So if we take the correct SHC of 4.186 and multiply by my 4m we should get to your 19.64m, and what is very interesting, is that we don't.

Hang on, I'll dig out me workings (shuffle shuffle):

--8<------------------------------------------
Distance from which you'd have to drop a 1 tonne mass in order to boil 0.5 Litres of water:

Energy required to raise temp of 1cc water by 1 degree = 1 joule [wrong!].

So energy required to raise 500ccs water by 80 degrees = 40,000 Joules

So we need 40KJ from our 1-tonne mass.

E = mgh so h = E/mg

= 40,000 / (1000 * 9.8)

= 4.0816326530612244897959183673469, otherwise known as "four".
--8<------------------------------------------

So why did that not work, then? Ah! Your second specific heat capacity is wrong, you've typo'd it to 4.816 instead of 4.186.

If we do 4.186 * 4.08 we get (tappity tap) 17.07888 (as opposed to your 4.816 which gives us 19.64928, perilously close to your 19.64).

The final answer, then, is just over 17 metres, so I can safely say that what I was getting at, which is that if you want me to make you a cup of tea by lifting and dropping a heavy weight a long way you can forget it, still stands.

Thank fuck for that. I was beginning to think we might have to rewrite maths. And I don't know about you but I'm busy all next week.

:bu:

--
simon

:bu:

So that would be a need for 40 kilocalories..

Less than half a bar of chocolate or more specifically this 107kcal of 2 fingers of Christmas Pudding flavour Kit Kat.

So using one finger I could boil a kettle.
--
Julian

Now, that I'd pay to see :)

--
bombholio

:bu:

Why did nobody tell me? Maybe it's not made it to the frozen north.

--
pw1