An illustration of Newton's First Law: "A cat at rest tends to stay at rest."
It's well known that "cats always land on their feet". This sequence of
photos shows how they do this, making use of the conservation of their
angular momentum as they fall:
(1) The cat brings in her front legs while leaving her back legs extended.
This makes the moment of inertia of the front part of her body much smaller
than the moment of inertia of the back part of her body.
(2) She then turns the front part of her body to face downward. To converve
angular momentum, the back part of her body turns in the opposite direction,
but much less, because its moment of inertia is larger.
(3) When the front part of her body is facing downward, she extends her front
legs and pulls in her back legs - so that the moment of inertia of the front
and back parts of her body are now relatively large and small. She can now turn
the back part of her body to face downward. The front part of her body will turn
in the opposite direction, but by a much smaller amount, since its moment of
inertia is larger.
(4) When both parts of her body are facing downward, she is ready to land on
her feet!