Entry
Why is it impossible to achieve a completely vertical, stiff position through entry when diving?
Diving
The rules state that the body should be vertical, or nearly so, for entry. Strictly speaking, it is physically impossible to achieve a literally vertical position throughout the entry as there will inevitably still be some rotational momentum while the body is entering the water. Divers therefore attempt to create the illusion of being vertical, especially when performing rapidly rotating multiple somersault movements. One technique is to allow the upper body to enter slightly short of vertical so that the continuing rotation leaves the final impression of the legs entering vertically. Another is to use "entry save" movements of scooping the upper body underwater in the direction of rotation so as to counteract the rotation of the legs. The arms must be beside the body for feet-first dives, which are typically competed only on the 1m springboard and only at fairly low levels of competition, and extended forwards in line for "head-first" dives, which are much more common competitively. It used to be common for the hands to be interlocked with the fingers extended towards the water, but a different technique has become favoured during the last few decades. Now the usual practice is for one hand to grasp the other with palms down to strike the water with a flat surface. This creates a vacuum between the hands, arms and head which, with a vertical entry, will pull down and under any splash until deep enough to have minimal effect on the surface of the water (the so-called "rip entry"). Once a diver is completely under the water they may choose to roll or scoop in the same direction their dive was rotating to pull their legs into a more vertical position.