The Physics of Martial Arts is very much like the Physics of nature. When studying Martial Arts, it is important to understand and utilize potential and kinetic energies correctly.
In nature, potential and kinetic energy is often symbolized with a spring. At rest, the spring has a great deal of potential, energy which is stored but not yet utilized. As the spring is set in motion, the potential energy changes to kinetic. Through its cycle, the energy is constantly cycling between potential energy at the stationary ends of the spring to kinetic. This ease and flow of energy within nature exemplifies the non-destructive properties of energy. Energy isn't simply created, it's transferred from one state to another. The greater the potential energy of an object, the greater the kinetic.
The basic translation of energies into the Martial Arts world is relatively simple and straight forward. Translate that into the Martial Arts world. We have potential energy while we are in a stationary position. We have kinetic energy while we deliver the strike.
However, we can go deeper in this investigation of energies to understand and improve our Martial Arts even further. If we study physics, we learn that energy is always in motion and always shifting between potential and kinetic energy. The burst of kinetic energy is the strength of the strike. Based on the law of conservation, energy can neither be created or destroyed, the energy for this strike must come from somewhere.
The most simplistic view is that the energy comes from the recoil, meaning the potential energy of your strike is based upon how far back you can pull your arm or leg for the strike. While this can attribute for some of the potential energy available for your strike, this by no means represents all. After all, if it did, that would mean the person with the longest arms would always deliver the hardest punches.
Rather, we must think of the motion being potential energy, not kinetic energy, for the strike. What is happening when you begin to move into your strike is the potential energy of your body is being translated to kinetic energy for the body. This kinetic energy for the body is being transferred to potential energy for the strike rather than returning to the body. Energy is not being created or destroyed, simply transferred from one state to another.
Now the potential energy of the strike, which determines the maximum kinetic energy and thus the power of your strike, is based not only upon the recoil but also the movement of the body. The energy pool is further increased by the amount of potential energy you can transfer from the kinetic energy (movement) of your target. This is what the common phrase of "using your opponent's momentum" refers.
Learning to harness these different energies into your potential strike is what makes even the smallest movements quite powerful. However, the downfall for many people is learning how to control the conversion of this potential strike energy into kinetic strike energy.
Because in the most simplistic terms, we equate movement with kinetic energy, the tendency is to utilize our potential strike energy within the movement of our body, not in the final impact. The most evident sign of this is the increase of tension within the arm or leg as one approaches the target. Tension is the transference of the potential energy of the strike back into the muscles of our body. Thus, if a Martial Artist can learn remain relaxed and free of tension until the moment of the strike, they do not waste any energy and have the full pool of potential energy to strike with.
Understanding the flow of energy and how the basic physics of nature apply to strikes can help one become a better Martial Artist. Understanding must come not only from where and how the energy can be collected but also how to convert or release the energy back out.