When you do a belly flop, you feel a stinging pain and your skin can even get bruised. Have you ever thought why do belly flops hurt? Although water seems soft enough when you’re playing in it. Its surface is actually fairly hard, especially when you enter it at a certain speed. Due to the surface tension of the water, you have to break the surface of the water to enter.
When you do a swan dive, your hands part the water, creating an entry point for the rest of your body to slide gracefully — and painlessly — into the water. When you do belly flops, however, the entire flat surface of your whole body has to break the water to enter.
Simple physics holds that the larger the surface area of the body hitting the water. The larger the resistance force of the water pushing back will be. When your body falls flat with a bit of speed on the water from a distance. It creates a big impact that can feel a bit like falling on concrete.
When you belly flop into a pool, your body has a bit of kinetic energy, which is energy of motion. While you fall flat on the surface of water, that kinetic energy gets converted as your body suddenly decelerates upon impact with the water.
Some energy turns into the loud slapping sound you hear. A lot of the kinetic energy gets transferred to the water, which rushes out of your way and creates a big splash and waves. Some energy also converts to heat on your skin, which creates the stinging pain you feel. This is the reason why belly flops hurt.
While most belly flops don’t cause serious injury, they certainly can. If you were to do a belly flop from the high dive, you could certainly run the risk of injuries much more serious than stinging skin and a few bruises.
Abdominal injuries that affect internal organs, such as the liver, kidneys, pancreas, and bowels, suffer as a result of belly flops from great distances.
Content for this question contributed by Shawn Smith, resident of Albany, New York, USA