Right now, Jack In The Box is running an ad that should irritate scientists and thermodynamic engineers everywhere.

In the ad, Jack In The Box claims that the construction of their "Ultimate Cheeseburger" is superior to conventional cheeseburger construction because they place the condiments (lettuce, pickles, tomatoes, etc.) beneath the meat instead of on top of it. The claim here is that the condiments will thus remain cooler, because "everybody knows heat rises!"

Unfortunately, this claim constitutes a Gross Conceptual Error. The common expression "heat rises" is actually an abridged truth...

Heat does not rise - heat is thermal energy, and is massless. What does rise is a hot fluid in a colder fluid enviroment. This is known as thermal convection. So - hot air rises from a radiator, and hot water rises from the bottom of a kettle on a stove because they are less dense than the surrounding cooler air or water, but heat itself does not rise unless there is some medium of variable density to convey the thermal energy.

So - the problem is this: there is no air circulating inside an Ultimate Cheeseburger. The heat from the meat in any cheeseburger is conveyed to the condiments by thermal conduction, and this transfer of thermal energy occurs at exactly the same rate regardless of whether the meat is above the condiments or vice versa.

Another glorious example of advertising license, or just plain old stupidity?

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