My acceleration is zero. If I took my chair to the top of a mountain and sat in it, my acceleration would still be zero at that time. My speed might change, but my acceleration is relative. I'm not speeding up or down (actually, if I recall correctly, the rotation of the Earth is slowing by a very small amount, so technically my acceleration would be negative...I could be wrong about that.)
As for the amount of matter below me, ummm...from a relative perspective, the entire Earth is below me, so the amount of matter is the same. Now, if you consider all of the matter that is visible in the Universe from the opposite side of the world at any given time, that probably changes with the rotation of the Earth throughout each day, but the measurement would be so gargantuan that it really doesn't matter (pun intended.)