When an object collides head-on and in line with two balls in contact, the outcome is not generally
easy to predict. We consider three simple examples. One is Newton?s cradle with only three balls.
Another is a billiard cue colliding with the two balls. The third is a croquet shot where a mallet
collides with the two balls. The outcome in each case is different since it depends on the mass of
the colliding object.