BALLS: Happy, Unhappy

BALLS: Happy and Unhappy

• Two balls of 25mm diameter apparently identical, do not behave the same when dropped or rolled because of their differing physical properties.
• The ‘happy’ ball bounces when dropped whereas the ‘unhappy’ ball hits the ground and stays there.
• When the balls are cooled below room temperature, the ‘happy’ ball bounce reduces and the ‘unhappy’ ball bounce increases.
• Instructions included.

(Wikipedia excerpt: .."...The physics of a bouncing ball concerns the physical behaviour of bouncing balls, particularly its motion before, during, and after impact against the surface of another body. Several aspects of a bouncing ball's behaviour serve as an introduction to mechanics in high school or undergraduate level physics courses. However, the exact modelling of the behaviour is complex and of interest in sports engineering.

The motion of a ball is generally described by projectile motion (which can be affected by gravity, drag, the Magnus effect, and buoyancy), while its impact is usually characterized through the coefficient of restitution (which can be affected by the nature of the ball, the nature of the impacting surface, the impact velocity, rotation, and local conditions such as temperature and pressure). To ensure fair play, many sports governing bodies set limits on the bounciness of their ball and forbid tampering with the ball's aerodynamic properties. The bounciness of balls has been a feature of sports as ancient as the Mesoamerican ballgame.[1]...")

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