I'm not questioning his law or anything, I just need to understand a few things about it. I understand the basic concept of the law, for every force, there is an equal force in the oppostite direction. But what provides the reaction force in the following situations? A car driving, has an applied force forward, but what's the reaction force backwards? Also, in the same situation, what about friction? It applies a force backward, so what's the reaction force forward provided here? Second, a person lifting weights, they apply a force upwards to lift the weight, what is the reaction force here provided by? Also, how would the motion work in these cases? Assuming there's a car applying force forward, and the reaction force going backwards, the car accelerates forward, so the car must have a lesser mass than the object providing the reaction force, right? Or is it the other way around, and also, same with friction, it accelerates the car backwards, so then the mass of the object providing friction must be smaller than the mass of the object providing the reaction force forward, or is this backwards too? I can't think of any more, so that's all for now. Someone please help soon, thanks in advance.