how big would the coefficient of static friction between the upper and lower block have to be so that the upper block would not slip on the lower block?

the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface.

the answer is d. matter from the air combined with the steel wool.