Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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]

share|cite|improve this question

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

  • This question does not appear to be about physics within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

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
up vote 3 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].

share|cite|improve this answer
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

Not the answer you're looking for? Browse other questions tagged or ask your own question.