In teaching motivation for the third law I have found unfailing success in
"Socratically" uncovering a scenario like ==>
"Suppose I had an object A which repelled another object B, without object A
experiencing any force. I could then fasten them in-line on the floor of my
little red wagon and magically achieve effortless and free self-locomotion."
Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
www.sciamanda.com