Newton’s third law of motion states that to every action, there is always an equal and opposite reaction.

The law of motion involved in the recoil of gun is Newton’s third law of motion.

Feeler gauges are used:
– To check the gap between the mating parts
– To check and set the spark plug gaps
– To set the clearance between the fixture (setting block) and the cutter/tool for machining the jobs
– To check and measure the bearing clearance, and for many other purposes where a specified clearance must be maintained.