When the radius of the sphere "goes from r to r+ dr" the volume goes from to . The difference is . If we take dr sufficiently small that we can ignore the much smaller and that would be the differential .
When the radius of the sphere "goes from r to r+ dr" the volume goes from to . The difference is . If we take dr sufficiently small that we can ignore the much smaller and that would be the differential .
Well said, but for clarity, I just want to correct the small typo at the end. .