Before a diver jumps off of a springboard, he does a sort of hop-skip step called a hurdle. After doing a few steps, the diver leaps up into the air with his arms raised. When he lands back down on the tip of the board, he swings his arms down past his legs and then up, leaping into the air and off of the board.
The purpose of this hurdle is as follows:
A diver cannot simply stand on the end of board, step off, and expect to have the power to go up or the momentum to rotate his body in any direction. What the hurdle does, is first to allow the diver to use the diving board as a slingshot, and second get as much energy as possible out of the "slingshot".
This is achieved when the diver takes the first leap into the air with his arms raised. When he comes back down on the board, his own mass falling onto the board will apply a certain force. An additional force is added as the arms swing down at the same time with a greater acceleration, applying more force. At the bottom of the diving board's oscillation, all of the now stored potential energy is released. The diver swings his arms upward and begins to release his pressure on the board. The board pushes the diver up and into the air with a huge force.
This force now can be used by the diver not only to go up, but to rotate and therefore perform various dives.
The Dives and Application
To do a front dive a diver pushes his hips upward just slightly as he leaves the board. After he had begun to go up into the air, he throws his arms downward just enough to make is upper torso rotate around his hips. At the peak of the dive, the diver tightens his stomach muscles and pulls his legs up towards the sky, leaving his body in a perfect upside-down position to enter the water head-first.
In order to perform a front dive with a somersault, it requires a full flip of the body and therefore it takes a quicker rotation to cover such an angular distance. The diver takes off from the...