No matter how you swim or what stroke you are doing, chances are that you are applying physics to your path in the water. There is the speed at which you are going, the massive resistance from the water, etc.
When you dive into the pool, you are launching yourself from an initial velocity of zero into the pool. You want to maximize your displacement. You want to go as far forward in the air as possible, but you also want to stay shallow in the water as you make contact. To do this, you are incorporating many examples of physics into your start.
Also, whenever you are moving through the water, you are affected by gravity, normal force, and the force of the water. When you move your arms and kick your feet, you are accelerating yourself through the water. By pushing the water, you are propelling yourself forward. Unless you can't swim. In that case, the force of gravity is pulling you under the water.