Not only is the Universe stranger than we think, it is stranger than we can think. ~ Werner Heisenberg
While physics is derived from the Greek for “knowledge of Nature,” its locus is the study of moving matter. A central concern of physics is energy: what it takes to get matter to work. Work is the product of a force applied to matter. Work refers to a transfer of energy, often to matter. Work can be said to be energy in transit.
To understand motion is to understand Nature. ~ Italian polymath Leonardo da Vinci
German physician, chemist, and physicist Robert Mayer enunciated in 1841 one of the original statements on the conservation of energy: that “energy can be neither created nor destroyed.” The implications of this statement came to be interpreted too literally by those insufficiently meticulous about their philosophy of physics.
Energy is usually presented in the following way: “energy can neither be created nor destroyed but only transformed.” If energy cannot be destroyed, it must be an existing thing. If its form changes, it must be something real as well. Thus, that statement can easily lead to the concept of energy as something material. Robert Mayer did not find, however, anything like a substance but rather a methodology for dealing with phenomena. ~ Portuguese physicist Ricardo Lopes Coelho
Energy is nothing but a convenient concept: a way of characterizing observed changes in matter. Energy is merely a quantitative property – a measure of what it takes to put matter in motion. Energy does not exist.
The subtle and intellectually difficult concept of energy, with its associated mathematical splendor, permits the integration and use of mechanics. ~ American biomechanist Steven Vogel
Changing motion – the velocity of matter accelerating or decelerating – concerns physics greatly. The relation between energy and speed is quadratic: double the energy is required to incrementally change speed.
The energy associated with motion is kinetic energy. Gustave-Gaspard Coriolis developed the modern concept of kinetic energy in 1829.
Temperature is an approximate measure of the kinetic energy of molecules. More formally, the kinetic energy of an object is measured by its movement. The measure of kinetic energy (E) depends upon the mass (m) of a moving object and its velocity (v): E = ½mv2.
Energy related to position is potential energy: energy stored that may be released. Scottish mechanical engineer William Rankine coined the term potential energy in 1853. A ball lifted into the air has potential energy, because, if released, gravity would work on the ball to have it drop to the ground – in the process, turning potential energy into kinetic energy.
An atom has potential energy which is released if the atom’s nucleus starts to decay, thus radiating energy; or if the electrons of an atom are diverted to work elsewhere: somewhere other than clouding the home nucleus with a wondrous whirl.
Matter has mass. Mass is not weight, though it is commonly expressed as such. Instead, mass is a measure of matter’s inertia: indisposition to a change of motion, regardless of whether the object is moving or at rest.
Mass is measured in kilograms (kg). Weight is a force, measured in newtons (N).
Energy does not exist in a myriad of forms: mechanical, thermal, chemical, radiant, atomic, and quantum. Theoretically, different forms of energy are interconvertible. Actuality renders this energetic fluidity a polite fiction seemingly full of exceptions. As constrained as matter in its specificity, energy works its magic in distinct domains. The appearances of energy are always statements made on matter: either retarding or accelerating transitions which, ultimately, are nothing more than expectations and their confounding.
It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we can say about Nature. ~ Danish physicist Niels Bohr