Gravity, forces, spacetime, acceleration conundrum If gravity is not a force but rather spacetime curvature, why when standing on a scale do we say the "normal force" the actual force that the scale is measuring? Is the normal force caused by mass in the sense that it is not spacetime curvature but an actual force?
If you stand at the edge of a cliff and do not fall, is it the result of normal force or is it the electromagnetic force? Isn't the electromagnetic force quite powerful?
 A: I will interpret the first part of your question as meaning how does gravity work on the Earth's surface. I will not answer the second part, about why a falling body passes freely through the molecules of the atmosphere, as that is a separate one, and you should post it separately.
I suggest you try to think of it this way...
When you stand on the edge of a cliff, you are moving through spacetime. Your spatial coordinates are fixed (in the frame of the cliff), so all your forward motion is in the direction of time. Because spacetime is curved in the presence of the mass of the Earth, your natural motion through spacetime is to follow a path known as a geodesic- that means that as you move forward in time, your spatial coordinates would change in a way that moved you closer to the Earth's centre of mass. However, what is stopping that is the presence of the cliff which is impeding the free movement of the soles of your feet.
So you are continually being prevented from following a geodesic by the electromagnetic forces between the cliff and your feet. If the cliff magically disappeared, you would be free to follow the geodesic again, moving closer to the centre of mass of the Earth until you found the next obstacle that impeded you, namely the ground at the foot of the cliff, when once again the electromagnetic forces at play between the ground and your body would continue to deflect your movement so that it followed only the time direction.
Of course, the ground too would like to follow a geodesic- it has been prevented from doing that by the presence of the next layer of ground beneath it, and so on.
So, in effect, the earth is at an equilibrium of sorts, caused by a combination of electromagnetic forces, which prevent the matter of the the Earth from coalescing more tightly, and the spacetime curvature caused by the mass of matter, which would otherwise cause all the particles that comprise the Earth to move forward through spacetime on geodesic paths that brought them closer together.
A: First the picture from classical mechanics: if an object is at rest or at constant velocity in an inertial frame, the sum of forces must be zero. The scale displays a force on it. This force comes from the object above. According to the $3^{rd}$ Newton's law the scale makes a force of the same magnitude and opposite direction on the object. But the object is at rest. Conclusion: there is a force of gravity on the object, with the same magnitude and opposing direction to the force from the scale.
According to GR, if the sum of forces is zero, the object follows a geodesic. Being at rest on the scale is not following a geodesic. So, the sum of forces is different from zero. The origin of the (normal) force is electromagnetic. It is also valid when the object is falling and suffering drag force from air or water. It's path is not a geodesic, what means that the sum of the forces is not zero.
