In section 11.5 in exercise 11.6 on page 273 it says parenthetically:
(dropped objects do not spontaneously start to rotate)
Actually many things do spontaneously start to rotate. For example, as the proverb says, a cat always lands on its feet. If you drop a cat from some moderate height with zero initial angular momentum, it will flip around in mid-air. People do the same thing to some extent. Apparently it's partly instinctive; I've seen little kids do it, kids with no training, kids far too young to have any theoretical understanding of angular momentum. Also it's partly learned; little kids learn balance via activities such as walking on a narrow curb. Trained performers such as acrobats and divers carry this to extremes.
The physics is simple: Angular momentum is conserved ... but angular position is not. Objects with moving parts such as arms, legs, and/or tails can rotate in mid-air just fine. Also satellites in orbit can change their orientation at will, even when there is nothing to push against.
In section 11.5 in exercise 11.6 on page 273 it says parenthetically:
Actually many things do spontaneously start to rotate. For example, as the proverb says, a cat always lands on its feet. If you drop a cat from some moderate height with zero initial angular momentum, it will flip around in mid-air. People do the same thing to some extent. Apparently it's partly instinctive; I've seen little kids do it, kids with no training, kids far too young to have any theoretical understanding of angular momentum. Also it's partly learned; little kids learn balance via activities such as walking on a narrow curb. Trained performers such as acrobats and divers carry this to extremes.
The physics is simple: Angular momentum is conserved ... but angular position is not. Objects with moving parts such as arms, legs, and/or tails can rotate in mid-air just fine. Also satellites in orbit can change their orientation at will, even when there is nothing to push against.