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We know that i)avg speed of A Hamster is 30km/hr. ii)Avg mass of hamster is 1.5 kg.

From the above info:

Kinetic energy=1/2 X mass X velocity^2

So, K.E=1/2 x 1.5 x 30 x 30

  =1/2 x 3/2 x 900


=675 J per hr.

In one second,=675/3600 =1/5 j/s

but power needed is 15j/s to light a CFL.

75 Hamsters would have done that.

if I catch 75 hamsters,and run them for an hr,can I light a bulb

[NOTE:-Just applied my 14 yrs old brain...pls correct if I am wrong..also,please tell me why are hamsters used in experiments]

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closed as off-topic by Chris White, Dilaton, David Z Aug 2 '13 at 20:41

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You messed up the units. You need to put the velocity in terms of m/s and not km/hr. the KE will be $625/12 J \approx 50 J$ per hamster, and not $675/3600 J/s$. –  udiboy1209 Aug 2 '13 at 15:33
Keep in mind the difference between energy and power. The kinetic energy of a hamster a top speed is not the same as the power expended by the hamster. Power is the rate of change of energy. –  Michael Brown Aug 2 '13 at 15:38
@udiboy can you please mention how did you get 625/12J –  Sid Aug 2 '13 at 15:41
The average mass of a hamster is about an order of magnitude smaller than stated in the question. A typical adult hamster weighs in at 5 ounces (0.14 kg). –  Johannes Aug 2 '13 at 16:19
@ChrisWhite I think it is more about the physics of energy. The source just happens to be biological. And I don't know why anyone would down vote a 14 year old asking a good question. –  user6972 Aug 3 '13 at 5:15

1 Answer 1

up vote 2 down vote accepted

How many hamsters do you need to power a 15 W light bulb?

I am going to treat this as a Fermi problem. Let's give a hamster a typical mass $m$ of $\ 0.15\ kg$. And let's assume this hamster can climb $\approx 0.6\ m/s$ against a gravitational acceleration of $\ g\ =\ 10\ m/s^2$. In doing so this hamster would generate $\ m g v\ =\ 1\ Watt$.

This leads to the estimate of 15 hamsters being needed to do the job.

As a check on this result, we can use Kleiber's law to upscale this estimate from the realm of rodents to that of humans. If we assume a typical human weight to equal that of 500 hamsters ($\approx 75\ kg$), Kleiber's law tells us we have to upscale the power by a factor $500^{3/4}\approx\ 100$. This leads to an estimate of a human being capable of generating $\approx 100\ W$. A very reasonable result: "adults of good average fitness average between 50 and 150 watts for an hour of vigorous exercise" [from: Wikipedia article on human power].

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So a capybara could power 20-40 light bulbs? ;) –  Michael Brown Aug 2 '13 at 16:42
@MichaelBrown I'd imagine that as king of the rodents, a capybara wouldn't stoop to powering light bulbs; it would just order some hundred hamsters to do it. –  Jim Aug 2 '13 at 16:58
You can find anything on the internet. I found hamsters run at about 0.8 m/s on flat ground (1.1 m/s tops). And to generate power there's going to be some additional force (friction) over just gravity and power loss (efficiency). –  user6972 Aug 2 '13 at 18:06
@user6972 - thanks, have slightly updated the estimate. –  Johannes Aug 3 '13 at 3:21
Looks good but that's still available power. The real electrical power has be generated from a hamster sized electric motor which on a good day is probably only 70% efficient or 0.7 W/hamster. –  user6972 Aug 3 '13 at 16:59

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