A snowball is a

spherical A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the ce ...

object made from

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...

, usually created by scooping snow with the hands, and pressing the snow together to compact it into a ball. Snowballs are often used in games such as

snowball fight A snowball fight is a physical game in which balls of snow are thrown with the intention of hitting somebody else. The game is similar to dodgeball in its major factors, though typically less organized. This activity is primarily played during ...

s. A snowball may also be a large ball of snow formed by rolling a smaller snowball on a snow-covered surface. The smaller snowball grows by picking up additional snow as it rolls. The terms "

snowball effect A snowball effect is a process that starts from an initial state of small significance and builds upon itself, becoming larger (graver, more serious), and also perhaps potentially dangerous or disastrous (a vicious circle), though it might be be ...

" and "snowballing" are derived from this process. The Welsh dance " Y Gasseg Eira" also takes its name from an analogy with rolling a large snowball. This method of forming a large snowball is often used to create the sections needed to build a

snowman A snowman is an anthropomorphic snow sculpture of a man often built in regions with sufficient snowfall and is a common winter tradition. In many places, typical snowmen consist of three large snowballs of different sizes with some additional ...

. The underlying physical process that makes snowballs possible is

sintering Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...

, in which a solid mass is compacted while near the melting point. Scientific theories about snowball formation began with a lecture by

Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...

in 1842, examining the attractive forces between ice particles. An influential early explanation by James Thomson invoked

regelation Regelation is the phenomenon of ice melting under pressure and refreezing when the pressure is reduced. This can be demonstrated by looping a fine wire around a block of ice, with a heavy weight attached to it. The pressure exerted on the ice sl ...

, in which a solid is melted by pressure and then re-frozen.

When and how

When forming a snowball by packing, the pressure exerted by the hands on the snow is a determinant for the final result. Reduced pressure leads to a light and soft snowball. Compacting humid or "packing" snow by applying a high pressure produces a harder snowball, sometimes called an ice ball, which can injure an opponent during a snowball fight. Temperature is important for snowball formation. It is hard to make a good snowball if the snow is too cold. In addition, snowballs are difficult to form with a dry powdery snow. In temperatures below , there is little free water in the snow, which leads to crumbly snowballs. At or above, melted water in the snow results in a better cohesion. Above a certain temperature, however, the snowball too easily becomes

slush Slush, also called slush ice, is a slurry mixture of small ice crystals (e.g., snow) and liquid water. In the natural environment, slush forms when ice or snow melts or during mixed precipitation. This often mixes with dirt and other polluta ...

, which lacks mechanical strength and no longer sticks together. This effect is used in the rule that, in skiing areas, there is a high risk of avalanche if it is possible to squeeze water out of a snowball.

Natural snowballs

Under certain unusual circumstances, natural snowballs form as a result of wind, without human intervention. These circumstances are: * The ground must have a top layer of ice. This will prevent the snowball from sticking to the ground. * That ice must have some wet and loose snow that is near its melting point. * The wind must be strong enough to push the snowballs, but not too strong. In Antarctica, small windblown frost balls form through a different process that relies on

electrostatic attraction Coulomb's inverse-square law, or simply Coulomb's law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is convention ...

; these wind-rolled frost balls are known as

yukimarimo Yukimarimo are balls of fine frost formed at low temperatures on the Antarctic plateau during weak wind conditions. Yukimarimo were discovered in 1995 at Dome F by the 36th Japanese Antarctic Research Expedition (JARE-36) at temperatures of –59 ...

. Under other rare circumstances, in coastal and river areas,

wave action In fluid dynamics, a wind wave, water wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result from the wind blowing over the water surface. The contact distance in the direction o ...

on ice and snow may create beach snowballs or ball ice. File:Jää on kulmunud pallideks (Looduse veidrused). 05.jpg , Ball ice File:Yukimarimo_south_pole_dawn_2009.jpg , Yukimarimo File:Snow roller (30 January 2014) (Newark, Ohio, USA) 53 (46107487244).jpg , Wind-rolled snowball File:Spongy ice ball Lake Street.jpg , Beach snowball showing signs of

denivation Niveo-aeolian or cryo-aeolian deposition is the process by which fine-grained sediments are transported by wind and deposited on or mixed with snow or ice. The wind sweeps the snow and sand grains into aeolian landforms such as ripples, and furt ...

Literary allusion

A snowball that turns into a child is a protagonist in a 1969 children's fantasy novel, '' The Snowball'', by Barbara Sleigh.University of Oxford librarie
Retrieved 14 September 2018.
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References

{{Authority control Ball Play (activity)