It helps to remember that “heat” is just “[how much the particles are wiggling](https://www.tec-science.com/wp-content/uploads/2019/01/en-particle-model-temperature-movement-thermal-expansion.gif)”.
Temperature is a measure of the *average* speed that something’s particles are bouncing around off of each other at.
With that understanding, it becomes easier to see how forcefully rubbing something generates heat – you’re directly adding mechanical energy to the system, and some of that results in the particles wiggling more than before. This means they have a higher temperature. You’ve “created heat”.
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