# Homework Help: 4 gallons, 52f to 145f energy?

1. Dec 25, 2012

### supak111

4 gallons of water to go from 52f to 145f, how much energy does it take?

Just saw a video of someone do it in 2 minutes using a 5hp motor or about 125 watts

2. Dec 25, 2012

### Bandersnatch

Convert the units to SI and use E=mgh

4*3,79{four gallons in litres}*9,81{acceleration due to gravity}*28,34{the height difference in metres}=4216 Joules

That's roughly 30 seconds for a 125W engine, assuming no losses.

In general, lifting things up require very little energy as compared to other everyday energy-intensive uses. E.g. heating a cup of water to the boiling point(aka making tea) consumes enough energy to lift the same cup to the height of 30km.

Also, Merry Christmas.

3. Dec 25, 2012

### supak111

So in other words doing it in about 2 minutes is only about 25% efficient using that much energy.

Thanks for the quick answer & Merry Christmas to you & everyone else as well

4. Dec 25, 2012

### Staff: Mentor

Um....is "f" feet or Fahrenheit? And 5 hp is 3730 Watts, not 125...

Clarification required...

5. Dec 25, 2012

### Bandersnatch

Heh, good points. Obviously I assumed height.

In the case of temperature, it takes ~213 Joules of energy to heat up 1gram of water by 51K(converted from Fahrenheit).
Four gallons require ~3230000 Joules.
Two minutes of operation of a 125W engine nets 1500J. A 3730W engine supplies 450000J in the same amount of time.(again, no losses)
Neither is nearly enough, so it probably was height after all.

6. Dec 25, 2012

### supak111

Actually it was 52 to 145 fahrenheit, guy was using a 5hp motor for 2 minutes to drive a hydrosonice pump which actually a lot of people have claimed has exibited overunity. Now this was all rought numbers, it was 2 mins and about 3sec, and I didn't see exactly how many watts he was pulling I'm just going of him saying its a 5hp motor maxed out.

7. Dec 25, 2012

### supak111

And yea its 5hp for 2 minutes so I figured you divide 5hp/3730 watts by 30 = 125W/sec or 125W/s x120 seconds= 15000J right? Or no?

8. Dec 25, 2012

### sophiecentaur

Watts per second is not a quantity that means much in this context. I think you need to examine your dimensions, in general and stick to Imperial or SI (Si, preferably). There is less possibility of getting mixed up if you use SI, I think. (I would say that, though!).

Also, there is not much point in looking at 'Over Unity' devices. The claimed over unity figures have to be wrong and are often arrived at by smoke and mirrors with Units (if not by just plain lying). PF excludes discussion of Over Unity, in any case.

9. Dec 25, 2012

### supak111

Oh I totally understand over-unity is 99.9999% crap, I just tend to give anything a change even if I'm only giving it a 1 in a billion possibility. As advanced as today's science is it probably still only knows a fraction of a % of how everything really works sooo I try not to be closed minded. But forget that actually I wasn't even going to mention why I was asking so we don't get into that, just kinda wanted to know for myself what kind of energy it would take.

10. Dec 25, 2012

### sophiecentaur

If you want examples of 'getting more heat out than energy put in' then you only need to look at heat pumps. They work. But by getting heat from a cold source and pumping it to a hot source. That's not over unity but it is 'good value' if you can make and maintain the refrigeration unit AND have a source of not-too-cold water / air / ground from which to extract your heat. There are working installations but it never seems to catch on because it needs to be in just the right location.

If you want a useful appraisal of this hydrosonic pump system, you need to get the units and quantities perfectly straight and also do a 'total costing' of the energy involved. The video in the link that is quoted doesn't show the rate of water flow. It uses the term 'thermosyphon' as if it's something special. It only means natural convection - as in the early central heating systems and the very first motor cars. If that tank of water really is all heating up more than is suggested by the kWhr supplied then something, somewhere is cooling down to provide that excess heat. It could even be the air in the workshop (same as the stuff in the fridge cools down so that the coils in the back get warm).

Just remember that 5hp is 5X760W = 3.6kW. A 3.6kW heater is fairly meaty and would even supply enough hot water for a meager shower. I think you have been misled by the 125W diversion.

11. Dec 25, 2012

### supak111

Again thanks for the explanations everyone

12. Dec 25, 2012