Newton’s third law of motion was discovered and formulated, during the
investigation of the fact that in all experiments it appeared that
“when ever a body exerts a force on a second body, the second body
always exerts a force on the first one”
Let us visualize and understand these phenomena with an experiment
For more -
http://smartlearnwebtv.com/iitjee/IITJEE/newton%E2%80%99s-third-law-of-motion/