1. The problem statement, all variables and given/known data This isn't a homework question, but I thought this would be the appropriate place for the thread. I am having trouble explaining Newton's Laws to my friend. His confusion lies in the fact that the second Law F=ma does not equate to the sum of Forces in The third Law. Ex. A bus, and a mosquito The mosquito and the bus collide, the Force of the bus on the mosquito is equal to the force of the mosquito on the bus. I tried to tell him they are equal. He seems to think that if (and these are totally made up numbers) Mb=100mg ab=4m/s^2 mm=.2mg am= .5m/s^2 then Mb(ab) =/= - mm(am), so the third Law is incorrect. 2. Relevant equations F=ma F=-F 3. The attempt at a solution I tried to explain the conservation of momentum for inelastic and elastic crashes, but he doesn't want to hear it. Does anyone have any ideas of how I can explain the third law using his not equal example? Thanks for the help in advance.