How long would you have to yell to heat a cup of coffee?
It’s a neat question. The idea is that sound transfers energy. That energy will hit the coffee and dissipate as heat, so by yelling at a cup of coffee you could heat it up. Except of course that you can’t. The coffee will be losing heat as you yell at it, and will cool from hot to room-temperature in a couple hours. And yet, the APS site gives this answer:
In other words to heat up a quarter liter of coffee 50 C it would take: 1 year, 7 months, 26 days, 20 hours, 26 minutes and 40 seconds
How did they get that? The answer, of course, is that they used a spherical cow.