equivalence principle
One of the postulates at the basis of general relativity: A freely-falling observer in a gravitational field does not feel gravity. More precisely: In a small region of space around an observer in free fall in a gravitational field, the laws of physics are ...
equivalence between mass and energy
Already in special relativity, it turns out that (relativistic) mass and energy are really no more than two different ways of looking at one and the same physical quantity. To every form of energy, there corresponds a mass - if you heat a body up, increasing ...
energy
Physical quantity with the special property that, in physical processes, energy is neither destroyed nor created, simply transformed from one form of energy to another. Some of the different forms of energy that are defined separately are kinetic energy, ...
ellipse
An ellipse is a planar curve. All points on the curve are located around two focal points, such that the sum of the distances to each focal point is equal for all points. Special cases of an ellipse are a circle (in this special case, both focal points are ...
elementary particle
Within the commonly accepted models of physics, certain particles are not built of even more fundamental sub-particles - they are themselves elementary. Examples for elementary particles are electrons, quarks and neutrinos, while particles such as ...
element, chemical
A substance that cannot be decomposed into more elementary constituent substances by the methods of chemistry. From a physics point of view, to every chemical element corresponds a specific atom which is defined uniquely by the number of protons in its atomic ...
electrostatic force
An action-at-a-distance-force that acts between electrically charged bodies merely because of the fact they carry electric ...
