How do crocodiles jump? In a video (Here), I saw crocodiles jump vertically about three meters without using any solid surface. The wonderful thing is that when they start to jump, their vertical velocity is approximately zero, unlike fish who jump using initial velocity. It seems that crocodiles create an upward force that counteracts gravity, because when they are rising, their velocity seems to be constant.
How is this possible? Could anyone explain this phenomenon using physics laws?
 A: The upwards force comes from the rather violent tail movement. When the rest of the body is out of the water, the tail still acts sort of like a hydrofoil pushing the crocodile upwards, only not with a linear but oscillating motion, and obviously it's rather instable but enough to get the whole animal up in the air for a short while.
A: If you look closely at the crocodiles' tails you'll see that they wave their tails from side to side to provide propulsion for the jump. Compare this to a fish swimming:

The side to side motion of the fish's tail propels it forward, and the crocodiles are using exactly the same sort of side to side motion to propel themselves upwards.
A: I've recently started trying to swim the butterfly. Unlike other swimming strokes, there doesn't seem to be any way to "go easy" and do a relaxing length of the pool: if I want to get my face out of the water to breathe, I essentially have to use the water to do a push-up.
Now if a scrawny guy like me can lift his chin a few inches out of the water using his scrawny arms, it stands to reason that a crocodile with a meter of muscle in his tail should be able to do better.
If you look closely at the videos you'll notice that the "constant velocity" part of the ascent only lasts while the thick part of the tail is underwater. Once the crocodile is far enough up that only the skinny end of its tail remains in the water, the ascent slows.
