Saturday, March 28, 2009

How Long Would You Have To Yell To Heat A Cup Of Coffee?

Physics Central at the APS website has frequently produced a lot of interesting things to raise the interest in physics. This is another one of them. They have produced a couple of posters that asked rather amusing questions. This time, they asked how long would you have to yell to heat a cup of coffee! :)

This is such a fun question, but besides putting something most people are familiar with into a physics question, there is a very valuable illustration here on how scientists, and especially physicists, approach something. This back-of-the-envelope calculation is often how we analyze something new or how we can consider if something might be reasonable enough to warrant a more careful pursuit. If one can make a quick estimation like this and come up with unreasonable or impossible parameters, it is often a good enough reason to pursue something else.

The other poster that they have so far at this point asks for how long it would take to fall through the center of the earth. I've seen such questions being asked in an undergraduate physics class.

Students, contact your teachers and ask them to get a copy of the poster from the Physics Central main page.



Ben Lillie said...

It's a cool question, but am I wrong to get annoyed that the answer they gave was a spherical cow? (They assumed perfect insulation.) In anything approximating the real world it can't be done.

ZapperZ said...

Yeah, they made quite a bit of assumption in deriving such a thing. For the length of time it takes to heat it up, a lot of heat would have escaped already.

I suppose one can look at it as the "shortest time" possible to heat the coffee.


Tom said...

Isn't the reference for sound 10^-12 W = 0 dB, so 80 dB is 0.1 mW, not 1 mW, right? That makes their answer too small by a factor of 10.