[FOM] proofs by contradiction in (classical?) Physics

[Ivan Antonowitz]

 Antonino Drago posted:
>>
Many results - also in mechanics - have been obtained (since the time of 
Stevin) by arguments relying on the impossibility of the perpetual motion, a 
principle from which no direct proof can be obtained.
<<

Galileo caused an intuitive crisis when he deduced that a cannon ball would 
continue to move forever if left alone. Any way of extracting energy would 
cause it to stop and halt its perpetual motion!

Ivan Antonowitz.