The Physics
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Speed of a Falling Hailstone

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Bibliographic Entry Result
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Cutnell & Johnson. Physics 3rd Edition. New York: Wiley; 1995: 215. "Suppose that the hail described there bounces off the roof of the car with a velocity of +15m/s" 15 m/s
Geerts, B. Fall speed of hydrometeors. (April, 2000). "Hail can falls much faster, because its diameter can be larger. Its fallspeed is approximately given by 1.4 D0.8 at sea level, the exact relationship depends on hail density and shape. For instance, a large hailstone of 8 cm (D=80 mm) weighs about 0.7 kg and falls at 48 m/s !" 48 m/s
Killmier, Sam. Exploring Unknown Quantities. Development And Application of a Stochastic Catastrophe Model with Output and Sensitivities [pdf]. The University of Melbourne, 2005: 14. "Research has found that a hailstone's terminal velocity is roughly proportional to the square root of its diameter, with a diameter of 1 cm corresponding to a terminal velocity of 50 km/h (Munich Re, 1984)." 13.9 m/s
Martínez-Frías, Jesús. Compositional Heterogeneity of Hailstones: Atmospheric Conditions and Possible Environmental Implications [pdf]. Ambio. 30, 7 (Nov. 2001): 450. "Hailstones can reach a speed of 90 mph (140 km hr–1) as they fall to the ground!" 40.2 m/s
Schneider, Stephen. Encyclopedia of Climate and Weather. New York: Oxford University Press; 1996: 381. "The largest documented hailstone was 144 millimeters in longest dimension. The fall speed of that hailstone was determined to have been 47 meters per second, or 105 miles per hour." 47 m/s
Koontz, Jim. What are the effects of hail on residential roofing products? [pdf]: 2. [see graph below] < 39.6 m/s
Leigh, Roy. Dissection of a dent: modeling motor vehicle hail losses. Natural Hazards Quarterly. 4, 4 (December 1998). [see graph below] < 42.5 m/s
Windloadings & Hail. Lafarge Roofing. [see graph below] < 32 m/s

Imagine having hundreds of rocks ranging from pebble to golf ball size hurled at you. That is what it can be like if you are out during a hailstorm. Hail can create major dents in cars, damages buildings, and even kill people through fatal head trauma.

A hailstone forms when liquid below freezing collects around a solid object such as dust particle or another hailstone. A hailstone falls to the earth when it becomes too heavy for an updraft to keep it up. Really large hailstones form when a hailstone bounces up and down between updrafts.

Due to the fact that hailstone do not come in one size all hailstones do not fall at the same speed. Typically the bigger the hailstone the faster it will fall. The other big factor is wind. Depending on the direction of the wind, it can slow down or speed up the hailstone. A third smaller factor is the shape of the hailstone because different shapes experience different amounts of air resistance.

Alicia Kosiba -- 2005