Heat can also be produced by the impact of imperfectly elastic bodies as well as by friction. This is the case, for instance, when we produce fire by striking flint against steel, or when an iron bar is worked for some time by powerful blows of the hammer.
Boys have a tendency to jump around a lot more than girls. Boys have that desire to want to dunk way more than girls do. It just never seemed like something we could truly fathom and do.