When sand is picked up by the wind and breaks down bigger rock why is this a physical change?

  concave means having an outline or surface that curves inward like the interior of a circle or sphere. so the mirror curves inward.

Inelastic is the answer your looking for.

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.