(Before I start, due to the use of vectors let me state I consider up to be positive and down to be negative) Imagine a scenario, of a man in an elevator. And the elevator is accelerating upwards. Now in this case the Normal force > weight. So Normal Force - Weight =mass X acceleration. If you think this is right, why? Shouldn't it become Normal Force + Weight = mass X acceleration, because for weight(mg) the g will be -9.8 and hence -m X -9.8, will give you a positive value of weight. I know its prolly wrong, because it would be insane to add Force and weight when their difference is what gives me the acceleration upwards, but then again why exactly is -9.8 wrong?