## Physics Question #101

Marcel Leone, a 31 year old male from the Internet asks on December 7, 1999,

Is gravity considered to be one of the forms of energy such as electricity, heat, light, mechanical, etc.?

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### Barry Shell answered on December 7, 1999

Gravity is not a form of energy, but is a force of nature. Modern physics now recognizes four fundamental forces in Nature:

• Gravitational force
• Electromagnetic force which includes magnetism and electricity
• The Weak force and the Strong force - the two subatomic forces that hold the nuclei of atoms together.

(The Qi force so often referred to in alternative medicine, or any other new-age psychic forces are not recognized by science because they cannot be reliably measured and quantified, however this does not mean they do not exist. Maybe they do, but not in our current scientific framework.) Energy is defined as force setting matter in motion. Examples of some types of energy are heat, light, motion (or kinetic energy), electrical, chemical and nuclear energy, etc. Oddly, we don't truly know what energy is. This remains one of the great mysteries of science. We know how to measure energy, how to define it, and we know lots of formulas and principles about energy that give nice consistent answers, but the true nature of the beast remains an unsolved mystery. The force of gravity itself is also one of the biggest mysteries since nobody has ever been able to detect a unit of gravity (a graviton) in the same way they have detected electrons, for electromagnetic force, or photons for light. We can observe how gravity works, but nobody knows why gravity works. Gravity is a unique force in that it is 1. Long Range, operating over cosmic distances, and 2. Always attractive, unlike electromagnetic force which can be both repulsive and attractive. The bottom line is that we don't deeply know much about gravity or any of the other forces of nature. We only know how to make calculations based on our observations of how they operate and so how to use these forces to do work. But as far as having any fundamental truths and deep knowledge about what these things are, this is still an open question and one of the big ones that physicists continue to wrestle with. Einstein died trying to figure this one out. He never did it. For more information about gravity, check out the Mad Scientist Network http://www.madsci.org.

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