S4.1 Preview
[A] The motion of a rigid body
When a rigid body is thrown into the air, we notice something simple
in its apparently complex motion: one special point in the object moves
as though
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This special point, the center of mass, forms the starting point for our study of the motion of collections (or systems) of particles, of which a rigid body is a special case.
By analysing the dynamics of the center of mass we discover a new fundamental law of nature: the law of conservation of momentum. We use this new law to analyse collisions between different bodies, which can be elastic or inelastic.