For the purposes of this question let a "physical intuition" be an intuition 
that is derived from your everyday experience of physical reality. Your 
intuitions about how the spin of a ball affects it's subsequent bounce 
would be considered physical intuitions.

Using physical intuitions to solve a math problem means that you are able to 
translate the math problem into a physical situation where you have physical 
intuitions, and are able to use these intuitions to solve the problem. One 
possible example of this is using your intuitions about fluid flow to solve 
problems concerning what happens in certain types of vector fields.

Besides being interesting in its own right, I hope that this list will give 
people an idea of how and when people can solve math problems in this way.

(In its essence, the question is about leveraging personal experience for 
solving math problems. Using physical intuitions to solve math problems is a 
special case.)

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[These](https://mathoverflow.net/questions/30149/examples-where-physical-heuristics-led-to-incorrect-answers) [two](https://mathoverflow.net/questions/27943/in-what-ways-is-physical-intuition-about-mathematical-objects-non-rigorous) MO questions are relevant. The first is aimed at identifying when using physical intuitions goes wrong, while the second seems to be an epistemological question about how using physical intuition is unsatisfactory.