Need help with a question on volts and human energy

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mwong
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Need help with a question on volts and human energy

Post by mwong » Tue Feb 11, 2003 9:39 am

I'm putting together a report where I'd like to compare the output of a human being's energy to a battery...say, a 100 volt battery.<p>But I'm not sure if it is possible to prove this point scientifically, and if there are any websites out there that can gauge this type of measurement. How are volts tabulated, and what units of measurement are there to calculate human energy? Can they be linked? <p>Please help, and respond to me as soon as possible. thanks, L

bridgen
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Re: Need help with a question on volts and human energy

Post by bridgen » Tue Feb 11, 2003 11:03 am

I think you need to do a little more reading/research, but the following should get you going. <p>The volt is the unit of electromotive force, not energy. <p>The unit of electrical energy is the joule, which is equal to 1 watt-second. <p>The unit of heat energy (as expended by the human body) is the calorie, (hence all the fuss over calorific values of food.) <p>1 calorie = 4.2 joules. <p>A physical training instructor, or maybe a physiotherapist should be able to give you some idea of how to measure the body's energy expenditure. <p>Regards.

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Re: Need help with a question on volts and human energy

Post by L. Daniel Rosa » Tue Feb 11, 2003 1:39 pm

Be careful of the calorie. Food is measured in Calories (notice the upper case letter). This is misleading as the measurement is kilocalories, but instead of calling them kcalories or kalories for short they capitalize the first letter. You'll never see any of us calling kilowatt*seconds 'Dgoules' ;)

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Re: Need help with a question on volts and human energy

Post by Will » Tue Feb 11, 2003 1:43 pm

I once heard that, on average, for the purposes of sizing an air conditioning system, human bodies put out heat at the equivalent of seven human beings to 1.0 kiloWatt i.e, on average, a human being would put out about 143 Watts. As you were told by the previous correspondent, Volts are not units of energy but of e.m.f In order to know how many Watts were connected with a particular voltage you would have to know what the associated flowing current value was i.e. in Amperes or, for short Amps i.e. 10 Amps at !14.3 volts would be 143 Watts. If the value of 143 Watts were correct for human beings then it would only apply if they were hanging about and doing nothing. If they were to start doing mechanical work then the output would be greater.
Watts are not units of energy but units of POWER and Power is the rate of production or usage of work or energy - as previously Joules are units of energy equivalent to one Watt.second i.e. a power source of one Watt would produce one Joule per second.
In English units mechanical work is usually measured in Foot.Pounds i.e. a force of one pound acting/moving a body through one foot through one foot would one foot.pound (ft.lbf) of energy. 33,000 ft.lbf/min = one Horsepower (hp) and one horsepower = 745.7 Watts. In SI or metric units the unit of mechanical energy is also the Joule which, as well as being approx. 4.2 calories of energy is also one Newton.Metre of mechanical energy i.e. a force of One Newton (1/9.80665 kilograms or 101.97 Watts)
The Calorie of food values is not the ordinary calorie i.e. the heat required to raise one gram of water by one degree Celsius but is the kilocalorie or 1,000 calories - In food value it is normal to use the word calorie in capitalized form i.e. Calorie to indicate that it means kilocalorie.
If a human consumes 2,500 Cal/day which I think is about normal then they would be producing 2,500,000 calories/day, which if you divide by 4.2 (4.1868) would give you Joules/day which you could reduce to Joules/sec and, thereby, have the answer in Watts. Will
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Re: Need help with a question on volts and human energy

Post by josmith » Tue Feb 11, 2003 1:53 pm

I believe a "food calorie" is in fact a kilocalorie which is 4186 joules. <p>I can't find any proof of this except for the common sense approach. Moderate excercise can burn around 600 calories per hour which converts to .935 horsepower hours. If a human body is 25% effecient that would come out to around .25 hp which sounds much more reasonable than .00025 hp.<p>That would translate to a 150 pound man climbing vertically at a around one foot per second.

mwong
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Re: Need help with a question on volts and human energy

Post by mwong » Tue Feb 11, 2003 1:53 pm

Holy cow, my eyes just hurt reading your replies! Very complicated stuff, and I VERY MUCH appreciate all of your assistance.<p>Please feel free to keep the information coming; I'm going to try and break all the information you had provided me in regular peoplespeak for non-technical folks like myself.<p>Thanks again.....mwong

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Re: Need help with a question on volts and human energy

Post by jollyrgr » Tue Feb 11, 2003 4:05 pm

I remember this vividly from High School health class. It is simpler to use 1 Calorie than using 1000 calories to mean the same thing. Just like using 1 K watt instead of 1000 watts.<p>Or the one I hate but know I have to get used to is:<p>1Rk for 1,000 Ohms. Now I know why the "old timers" kept using "kilo cycles" instead of kHz.<p>[ February 11, 2003: Message edited by: Jolly Roger ]</p>
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Re: Need help with a question on volts and human energy

Post by Dimbulb » Tue Feb 11, 2003 4:58 pm

The energy of a human being changes so an average can vary. An expert in this portion of physiology may go about this with more accuracy.<p>A football player may expend more than a truck battery while another may expend only a fraction<p>We multiply voltage times amperage to get Watts.

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Joseph
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Re: Need help with a question on volts and human energy

Post by Joseph » Wed Feb 12, 2003 2:45 am

The figure of a human being able to sustain about 1/4hp of effort is what I have often heard.

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Re: Need help with a question on volts and human energy

Post by vapor » Thu Feb 13, 2003 5:16 pm

Well, may I through my two cents in the pool...<p>You topic is very broad in scope. You probably need to reduce your topic to discussing the energy required to perform a specific task (work) and then relate that to the size of battery required to provide the same amount of energy. Unless you are into differential equations, you need to look at an "ideal" system. (A system where no energy is lost in the process and all force is constant.) Also, if you are looking at sustaining a process for a period of time, then you will need to use more complicated formulas. As for the Calorie measurements, you can go to a library and look at some diet books. Sometimes they have these tables in them.<p>This may be an easier topic. You can determine the amount of energy requried to, say, lift a weight of 100 lbs.<p>There are nutritional web sites that list the amount of "C"alories that you can burn (work performed) during certain physical activities. In fact, they even describe how many Calories you burn while being a couch potato (sedentary).<p>Here are some formulas that you might need.<p>power = energy / time<p>Power is measured in watts (W), energy is measured in joules (a script capital e) and time is measured in seconds (s)<p>solving for energy, you get:<p>energy = power / time<p>the power in the battery can be determined by:<p>power = current in amperes (I) * voltage (Electro-motive-force EMF represented by either E or V.)<p> P = I * E<p>Power can also be determined by the following:<p>power = current squared * resistance.<p> P=I^2 * R<p>This way of measuring power could be used to build an equivalent electrical circuit to compare the human body's system to.<p>My chemistry book states that the Calorie is equal to exactly 4.184 joules (J).<p>You might need the following:<p>Energy is measured in joules (J)<p>1 J = 1 kg * m^2 / s^2<p> where: kg is kilogram
m is meters
s is time in seconds<p>Joules = Watts (W) / seconds (s)<p>Work = Force * delta-x (Change in position)
Note: the word delta will be replaced in
a formula by an triangle symbol.<p>Energy is also expressed as:<p>energy (script Capital E) = Power (W) * time (s)<p>By manipulating these formulas, you can solve various problems involving energy, 'C'alories, watts, current and resistance.<p>A question for you is this: How old are you and what is your level of mathematics? There are a multitude of formulas that can help you if your mathematics level is high enough. Most of the other formulas require at least trigonometry, calculus or differential equations.
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