Snowball

A snowball is a spherical object made from snow, usually created by scooping snow with the hands and pressing the snow together to compact it into a ball.^[1] Snowballs are often used in games such as snowball fights.

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" 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.^[2] This method of forming a large snowball is often used to create the components needed to build a snowman.

The underlying physical process that makes snowballs possible is sintering, in which a solid mass is compacted while near the melting point.^[3] Scientific theories about snowball formation began with a lecture by Michael Faraday in 1842, examining the attractive forces between ice particles. An influential early explanation by James Thomson invoked regelation, in which a solid is melted by pressure and then re-frozen.^[4]