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A snowball is a spherical object made from snow, usually created by scooping snow with the hands, and compacting it into a roughly fist-sized ball. The snowball is often used to engage in games, such as snowball fights. Snowball fights are usually light-hearted and involve throwing snowballs at one's friends or family. 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 or "iceball", which eventually can be considered harmful during a snowball fight. 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", "snowballing" and "Y Gasseg Eira" are named after this process. Often a snowman can be created using this method of snowballing, to create the sections needed to build the sculpture. There are some temperature/humidity ranges that prohibit or restrict the formulation of a snowball. With a powdery snow, snowballs are difficult to form. 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. If a person is walking on snow and it squeaks, chances are the temperature/humidity level won't form a snowball, because squeaking means that the snow is dry. ==Self rolling snowballs== Under certain, rarely occurring circumstances, self rolling snowballs form on their own. These circumstances are: * The ground must have a top layer of ice. This will prevent the snowball from sticking to the ground. * That ice has to have some wet and loose snow that is near its melting point. * The wind has to be strong enough to push them. Yet, it cannot be too strong. * Also, gravity could cause the snowballs to form instead of the wind. Because these conditions have to take place at the right place in the right time, it is considered a phenomenon.〔(Rare self-rolling giant snow balls found in UK ), The Telegraph, January 8, 2010〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「snowball」の詳細全文を読む スポンサード リンク
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