I'm having a very hard time understanding the concept of a "Normal Force." The only framework with which I've come to terms with is imagining the Normal Force as the force exerted when object A comes into contact with object B which keeps object B from losing its macroscopic structural integrity. In another words, if I'm standing on the ground, the ground exerts a normal force on me to keep its structural integrity. This force has to be equal and opposite to the force I'm exerting on the ground, my weight. So the normal force the ground exerts on me is equal to my weight. Now the part that becomes very confusing to me is a scale. Say I'm on a scale and I see my weight. Then I jump up and then land on the scale. Well in order to jump up there has to be a force exerted on me that overcomes the force of gravity. So I have to use my muscles and convert chemical energy into mechanical energy to push down on the ground. Now the ground has to exert a greater normal force than my weight to keep its structural integrity and since this force will be greater than the force of gravity pulling me down I'll fly off the scale. At the moment which this happens of course the scale will say I'm fatter. Which makes sense since the scale measures the normal force exerted by the scale on me. Now when I'm landing the scale will also say I'm fatter right at the moment I land. This is confusing to me. On my way down to the scale from the top of my projectory, the only force that's acting on me is gravity. Therefore, when I land the force I'll impart onto the scale should be the force of gravity on me. But that's not the case. So F = ma = mg does not hold. Instead what we have is F = mg + ma. Where's that other ma coming from?