We have previously discussed how the special theory of relativity influences martial artists. There are other physical phenomena outside of classical physics (levers, moment arms, center of balance, etc.) that my also effect one's pursuit of martial arts. We would like to discuss the effects of gravity which is a topic covered by the general theory of relativity that Einstein proposed in the early 1900's. As you all probably know by now, we are held on the surface of the Earth by the force known as gravity. This is a characteristic possessed by anything with mass. Please remember that mass and weight are not the same thing. Mass is a constant as long as you don't approach the speed of light while weight is a measure of the interaction between two objects. Even a photon of light, which has an infinitesimal amount of mass, can have its path of travel altered by gravity of sufficient strength.
The general rule one can follow is, the larger the mass of the body, the larger the gravitational field around it. So, someone whose mass is 150 kg will have more gravity than someone with a mass of 80 kg. Gravitational interactions are also determined by the distance between two masses so that the force of gravity drops as a function of the distance squared between two objects.
How might this influence one's throws? Imagine moving in for a throw such as o soto gari. As you approach your opponent, the interaction of your two gravitational fields increases. This causes you to enter even faster until collision between the two of you occurs. Usually, this phenomena isn't noticed because shortly after that another collision occurs with the ground. Since the Earth has a much larger gravitational field than either you or your opponent, that collision is felt much harder. A similar thing can be seen in such martial arts as Karate where a fist going towards the opponent enters much quicker as the gravitational force of the opponent attracts it. Here, this collision is usually more noticeable because an unconscious body striking the ground doesn't notice anything.
Another way gravity might influence your throw is through the "sling-shot" effect often used in rocket voyages through the solar system. The sling-shot effect? This is in the realm of orbital mechanics which is determined by gravity. Imagine a simple elliptical orbit (shaped like an egg rather than a circle). This is the path that the planets, the sun and the moon follow. Let's compare the moon orbiting around the Earth to the throw ogoshi. The elliptical orbit of the moon means that the speed of orbit changes. Specifically, as the moon's center of gravity (center of mass) gets closer to that of the Earth, it speeds up; as its center of mass gets father away its orbit slows. In ogoshi, as tori enters for the throw, both people will begin to move faster because their gravity centers are approaching each other. If tori can manipulate uke's elliptical orbit just right, uke will sling-shot over tori just like rockets do when they go around planets. Unlike the rocket however, the orbit of uke will be cut short when he/she intercepts the orbit of the Earth. This will, of course, result in deceleration trauma. Because of the speeds involved in the sling shot effect, one needs to worry about relativistic effects (such as time compression). We had a Judo instructor who was so light and fast on his feet that it often seemed that you were on the mat before you realized you were thrown. Could this have been time compression in action?
Can this be used to advantage? One way is to choose only the largest of opponents. This way, the percussive aspect of your throw (both upon contact with you and with the ground) will be maximized. Isn't it true that people don't recognize the gravity of the situation until they hit the ground? Of course the disadvantage of an opponent with a larger gravitational field is that you may end up being the one who sling shots Earthward. A small problem to say the least; you will have to experiment to find the right opponent.
Finally, here's an experiment to try to see the effects of gravity on your throw. Why not use ogoshi again? You will need yourself, an uke and three or four others. What this should illustrate is how aligned gravitational fields alter your throw (much like Astrology and how alignments of the planets effect your life?). First, have the extra people line up close behind uke while you do your ogoshi. Then, have them line up behind you (leave enough room for uke to fall) and do ogoshi again. You should notice that your ogoshi is much easier when they are all lined up behind you because their gravitational fields pull uke into the throw. Finally, have them line up on one side of you. Now do your throw. You should notice that the position where uke falls is different from the previous times such that uke is pulled slightly towards the people next to you. (NOTE: To get this experiment to work, you really need to conduct it in zero gravity where the Earth's gravity won't effect you measurements. Maybe on the next space shuttle flight the experiment can be conducted; but please get the permission of your sensei before doing it.
We hope that you can see the weightiness of the above discussion and
that it has a positive effect on your nage waza.