Hi I'm confused about what an accelerometer actually measures. I downloaded an app that reads out the data of the accelerometer in my phone in all three dimensions. If I lay it flat on a table, it says something around 9.81 in the z direction and something around zero in the x and y directions. If I drop it (and record the data), the acceleration is about zero in all three directions. This somehow makes sense since one feels weightless when in free fall. But still, the phone is only accelerated in the second case, and shouldn't an accelerometer measure acceleration?