Here, you can derive that by numerical method, as follows:
F = m.a
m = F/a
So, here we can see when we decrease one, other increase by same effect; we can say they are "Indirectly Proportional" to each other!
Hope this helps!
It transfers and changes into different types of energy, this is why the ground feels hot when something moves fast over it.
To find or discover by investigation?