what is the difference between hail and ice pellets
Ice pellets Ice pellets are a form of precipitation consisting of small, translucent balls of ice. Ice pellets are smaller than hailstones[1] which form in thunderstorms rather than in winter, and are different from graupel ("soft hail") which is made of frosty white rime, and from a mixture of rain and snow which is a slushy liquid or semisolid. Ice pellets often bounce when they hit the ground or other solid objects, and make a higher-pitched "tap" when striking objects like jackets, windshields, and dried leaves, compared to the dull splat of liquid raindrops. Pellets generally do not freeze into a solid mass unless mixed with freezing rain. The METAR code for ice pellets is PL (PE before November 1998[2]).
Frost weathering The traditional explanation for frost weathering was volumetric expansion of freezing water. When water freezes to ice, its volume increases by nine percent. Under specific circumstances, this expansion is able to displace or fracture rock. At a temperature of -22 °C, ice growth is known to be able to generate pressures of up to 207MPa, more than enough to fracture any rock.[6][7] For frost weathering to occur by volumetric expansion, the rock must have almost no air that can be compressed to compensate for the expansion of ice, which means it has to be water-saturated and frozen quickly from all sides so that the water does not migrate away and the pressure is exerted on the rock.[6] These conditions are considered unusual,[6] restricting it to a process of importance within a few centimeters of a rock's surface and on larger existing water-filled joints in a process called ice wedging.