What exactly is kinetic energy? I know that kinetic energy is the energy that an object obtains by the virtue of its motion, but I need an exact answer. So, potential energy, like there are three main types, right? Electrical potential energy, gravitational potential energy, elastic potential energy. So, these three can be governed by fundamental forces. Like gravitational potential energy is due to gravity, and the electric and the elastic can be determined by the electromagnetic force. And other forces like frictional force can also be governed by the electromagnetic force. These all forces, these fundamental forces, are governed by the fundamental particles, right? So, what exactly is kinetic energy from a fundamental particle point of view? And if $E=mc^2$, then shouldn't an increase in kinetic energy also increase the mass of the body?
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Does this answer your question? What is kinetic energy? See also: https://physics.stackexchange.com/q/378300/226902 and this extended answer https://physics.stackexchange.com/a/14752/226902 – Quillo Mar 26 '24 at 15:42
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And if E=MC^2, then shouldn't an increase in kinetic energy also increase the mass of the body? Technically- NO. Increase in relativistic kinetic energy means increase in Lorentz gamma factor as per definition : $K_{rel} = (\gamma - 1)mc^2$ Usually physicists when talks about body mass- they are talking about mass invariant to reference frames, i.e. rest mass. This does not change as per body movement. What changes is mass response function output $\mathbb {f}(m) \equiv (\gamma - 1)m$. – Agnius Vasiliauskas Mar 26 '24 at 15:45
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2The concept of "relativistic mass" has fallen out of style, because it obscures the real essence of relativity theory. – Albertus Magnus Mar 26 '24 at 15:52
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do read kinetic energy part of https://physics.stackexchange.com/a/14752/283030 – Dheeraj Gujrathi Mar 26 '24 at 16:23
2 Answers
Kinetic energy is the ability of a body to induce motion upon some other body by virtue of the motion of the body possessing it being in a state of motion. In other words, like all forms of energy, kinetic energy is simply the capacity of a body to do meaningful work. It is differentiated from potential energy primarily because potential energy is typically thought of as a "configurational" energy of a system; energy that a system has by virtue of how it is instantaneously put together. The electromagnetic energy is a great example, as it only depends on the relative distance of the two charged bodies from one another. Of course, as long as they have a means to do so, systems will tend to lessen their potential energy by converting it into kinetic energy, or even by the creation of new particles with some amount of energy (i.e. photons).
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When one talks about fundamental principles, then it appears that within the context of the standard model, there are likely two true fundamentals, viz. energy and matter, which are in themselves interchangeable and therefore equivalent. The relativistic energy relation is given by: $$E=\sqrt{p^2c^2+m_0^2c^4}.$$ Here the idea is that energy itself is expressed in two main forms, e.g. energy associated with momentum or motion, and energy associated with rest mass, $m_0$. Subtracting off the part contributed by rest mass yields the kinetic energy: $$T=E-m_0c^2.$$ In this sense, kinetic energy as the energy associated with motion is rather fundamental. Essentially, quanta are found to have either mass-energy, energy of motion or potential energy; and any combination of the three.
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