The Anatomy of a Forward One and a Half Dive

  I was a competitive springboard diver throughout high school and will discuss the physics behind a “forward one and a half” (103C) in a tuck position, from start to finish.

In springboard diving, a major component of diving is having the diving board work to your advantage.  In order to do this, divers perform either a hurdle (for forward facing dives) or a board press (for rear facing dives).  Let’s look at a basic hurdle.  One of the most basic hurdles involves the diver starting several steps back along the board, taking four slow steps forward while gentling swinging their arms in pace with each step, and then taking one final leap forward to the very edge of the board.  At the edge of the board, several things occur.  As soon as the diver’s dominant foot lands on the end of the board, they bring their other knee up to make a right angle (this is called the “skip” at the end of the hurdle).  They then circle their arms all the way around from back to front.  Once they have landed on the board again and depressed it completely, the diver’s hands are above their head once again.  They proceed to jump up and throw their arms forward while pulling into a tuck position, grabbing their ankles.  Once the diver has completed one and a half rotations, they “kick out” by extending their arms and legs and tightening their core.

Now, in terms of physics.  As the diver progresses down the board for their hurdle, their mass exerts force on the board.  The end of the board acts as a spring, which they depress with their jump.  It is as it recoils to its normal position that they leave the board.  The diver holds their arms high above their head and swings them forward in a wide arc to generate momentum.  They then tuck in their body and grab close to their ankles.  Many people playing around on diving boards and doing flips without proper training will grab their knees as they rotate, but by grabbing one’s ankles, one decreases one’s radius, which allows for a faster rotation/greater linear velocity.  An added benefit is that it is less likely that the diver will lose their grip as they rotate.  When it is time to kick out, the diver throws their arms out above their head and kicks their legs straight again as well.  This is meant to increase the radius and slow down the diver’s rotation.  Half rotation dives (or those in which the diver enters headfirst) are typically easier to slow down because the diver throws out both their hands and feet compared to full rotation dives in which the diver straightens only their legs.  This is because their raised arms significantly increase the radius of rotation.

The board itself also possesses many physics properties.  In addition to acting as a spring, the diver exerts torque on the board as they jump on it.  Competitive boards are adjustable in this way and have a circular dial to rotate the fulcrum that the board rests on.  If the diver rolls the fulcrum forward, they decrease the lever arm of the boards and it is less “springy”/more resistant to motion.  If they roll the fulcrum backwards, the opposite is true and it is “bouncier.” 

Image links:http://springboardsandmore.com/wp-content/uploads/2015/06/70-231-524-G-550x413.jpg 

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