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This question already has an answer here:

Lets say you have a nice bowl of piping hot soup. You use your spoon and take a sip and realize its too hot. So you blow on it a few times and now its cooled enough that it doesnt burn your mouth.

Obviously, blowing on the liquid will reduce the temperature, but is that really what is cooling it? Or perhaps the heat is moving to the metal spoon?

Is blowing on the liquid cooling the liquid more than the heat being transferred to the metal spoon holding the liquid?

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marked as duplicate by Brandon Enright, tpg2114, ACuriousMind, John Rennie, Kyle Kanos Jan 20 '15 at 17:08

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ heat will be lost through the metal spoon , but not enough for our liking $\endgroup$ – Gowtham Jan 20 '15 at 16:39
  • $\begingroup$ @BrandonEnright While your link is interesting, it doesnt answer the question I asked. $\endgroup$ – Keltari Jan 20 '15 at 16:41
  • $\begingroup$ Of course I found the exact duplicate after answering... oh well. $\endgroup$ – tpg2114 Jan 20 '15 at 16:54
  • $\begingroup$ @tpg2114 Again, that doesnt answer my question. Perhaps I should edit the question to be more clear. $\endgroup$ – Keltari Jan 20 '15 at 16:57
  • $\begingroup$ @Keltari Fair enough -- that wasn't clear the distinction. I edited my answer to address that point specifically. $\endgroup$ – tpg2114 Jan 20 '15 at 17:00
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Convection.

Heat is a measure of the average translational kinetic energy of molecules. Molecules exchange kinetic energy through collisions with one another. Just relying on collisions alone however takes awhile for the heat to spread -- one "layer" of molecules bumps another and exchanges a small fraction of energy. This layer bumps the next exchanging a small fraction and so on.

By blowing on it, you are effectively moving away the "bumped" layers quite rapidly compared to letting them move around on their own. So you are continually introducing a new source of cool molecules to absorb the energy.

This is far more effective than the conduction through the metal spoon (which acts on essentially the same principles and will depend on the convection within the soup on the spoon as to how effective it is). Unless your spoon is made of copper or something far more conductive than the stainless steel typically used for silverware.

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