Imagine a block of mass $m$ placed on the ground. I slowly lift it up to height $h$. The work done by me on the block is $mgh$. This amount of energy is now stored in the block when it is at height $h$. This energy is called the potential energy of the block. From where did we get the word potential? Why is it called Potential energy?
$\begingroup$
$\endgroup$
3
-
2$\begingroup$ Actuality vs Potentiality is a basic distinction of Aristotle's Metaphysics and Physics. Thus, it was still "available" to Early Modern Scientists like Leibniz that introduced the modern concept of energy. See also Vis viva. $\endgroup$– Mauro ALLEGRANZAOct 12, 2021 at 10:33
-
1$\begingroup$ There's a semantics question and a philosophical question here. I'd say choose which one you're referring to and post on the relevant SE page (English.SE or Phil.SE). The answers below are, in my opinion, inadequate (a simple ELI5 explanation). $\endgroup$– Yechiam WeissOct 12, 2021 at 16:04
-
1$\begingroup$ When we have a block attached to a spring, and we move the block, is the energy in the block or is it in the spring? Gravitational potential energy isn't in the block. You can't measure it by measuring the block. You have to measure the system that contains the block. $\endgroup$– Phil SweetOct 12, 2021 at 19:45
Add a comment
|
4 Answers
$\begingroup$
$\endgroup$
5
potential (adj.)
Capable of being but not yet in existence; latent or undeveloped.
The block is stationary and therefore not performing work. If the block never moves, the potential energy remains unused, but "available." Energy was expended in order to place the block at $h$ height. Energy cannot be destroyed, but in this case, it can be stored.
answered Oct 10, 2021 at 11:03
-
$\begingroup$ But no form of energy performs work - work is by definition a transfer of energy. A flywheel spinning without friction stores kinetic energy, and precisely meets the exact same criteria of not performing work, and storing energy in an unused but "available" form. It seems you could apply this answer equally well to kinetic energy - "The flywheel is spinning at a constant rate and therefore not performing work. If it continues to move, the energy remains unused but available. Energy was expended to accelerate the flywheel to angular speed w, storing energy." But that's not potential energy. $\endgroup$ Oct 11, 2021 at 18:33
-
5$\begingroup$ @NuclearHoagie I would certainly classify a spinning flywheel as containing potential energy. Potential energy is reference frame dependent. Spinning the wheel up is not potential energy, it is storing energy in reference to spin up vs usable work from spinning it down. Spinning a flywheel faster and faster until it breaks is no different from adding weights to a string until it snaps in the right frame of reference. Potential energy isn't a fundamental property of an object. It is a descriptor in relation to something else. $\endgroup$– David SOct 11, 2021 at 22:20
-
2$\begingroup$ @DavidS If you classify the kinetic energy in a spinning flywheel as potential energy, then your classification runs contrary to all mainstream physics. Whatever point you are trying to make about different frames of reference, kinetic and potential energy are not the same thing. It's a little troubling to me that your comment has received so many upvotes on a site devoted to engineering. $\endgroup$– d_bOct 12, 2021 at 21:29
-
$\begingroup$ @J... Sure, the kinetic energy certainly depends on the reference frame, but I don't see what that has to do with potential energy. Changing reference frames doesn't transform the kinetic energy to potential energy. The distinction between kinetic and potential energy is definitely not arbitrary, and it persists even beyond elementary physics. (For example, it shows up when one does lagrangian or hamiltonian quantum field theory.) $\endgroup$– d_bOct 13, 2021 at 18:04
-
$\begingroup$ @J... I really disagree with the sentiment that all of this is arbitrary and that we can wave our hands and say "Eh, kinetic, potential, it's all the same thing." These things are well-defined and we can distinguish between them. Unfortunately I think we will have to agree to disagree, as this conversation has already grown beyond what is appropriate for these comments. $\endgroup$– d_bOct 13, 2021 at 18:49
$\begingroup$
$\endgroup$
2
Because it has the potential to produce mechanical work.
-
1$\begingroup$ @Fred_dot_u I upvoted your answer because it's correct. I just wanted to be (for once) as short in my answer as possible. ;-) $\endgroup$– NMech ♦Oct 10, 2021 at 17:57
-
1$\begingroup$ I think this answer is more precise. When we lift the block, the lifter did the work, the energy is stored in the lifter rather than the block. When stationarily hanging in the air, the block has no stored energy but has "the potential" to produce energy. $\endgroup$– r13Oct 11, 2021 at 22:38
$\begingroup$
$\endgroup$
2
In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, attachments, electrical charge, magnetic field, mass, etc., and external forces, spring force, electric charge, magnetic field, gravity, or others.
The term potential energy was introduced by the 19th-century Scottish engineer and physicist William Rankine, although it has links to Greek philosopher Aristotle's concept of potentiality. The concept of potentiality, generally refers to any "possibility" that a thing can be said to have. Aristotle did not consider all possibilities the same, and emphasized the importance of those that become real of their own accord when conditions are right and nothing stops them. Actuality, in contrast to potentiality, is the motion, change, or activity that represents an exercise or fulfillment of a possibility, when a possibility becomes real in the fullest sense.
The work of potential forces acting on a body that moves from a start to an end position is determined only by these two positions and does not depend on the trajectory of the body. The potential field can be evaluated at those two positions to determine work. This allows the set of forces to be considered as having a specified vector at every point in space forming what is known as a vector field of forces, or a force field. Furthermore, the force field is defined by this potential function, which is also called potential energy.
The term "potential" itself is a historical term that was carried into current practice, through the normal accident and convenience of the development of the physics and mathematics, from the natural philosophy at its root.
http://web.ecs.baylor.edu/faculty/lee/ELC5360/Lecture%20note/Potential%20Energy.pdf https://en.wikipedia.org/wiki/Potential_energy
-
$\begingroup$ This is a good answer. In physics, sometimes we need to create vocabulary and try to use terms that generally make sense, but in the end aren't tied to the exact definition of in traditional usage. Example, if I hold a 100 lb weight over my head, normal people would say I'm doing a lot of work. A physicist says I'm doing no work at all. Because "work" has a unique definition in physics. $\endgroup$– Eric GOct 12, 2021 at 22:20
-
$\begingroup$ The 'uniqueness' here isnt so much in physics, as it is in muscle tissue. A humanoid hydraulic robot performing the same task wouldnt be doing any 'work' in that scenario. You are doing no work 'on' the weight over your head; but your muscle fibers are doing work on the microscopic level to produce a static force. $\endgroup$ Oct 13, 2021 at 18:54
$\begingroup$
$\endgroup$
9
The block in itself has no energy. If you build a kettle of water around it, the water will not heat up. If you attach axles to it, the axles will not suddenly start spinning.
However, since we spent energy bringing the block up, the law on conservation of energy dictates us that we should be able to get energy back when we bring it down again. So... if we attach a cable to it, connected to a pulley and a generator, we can use it to generate electrical energy (which is done in practice. It's called a mechanical battery).
So, the rock has the potential to give energy. Hence, "potential energy".
-
1$\begingroup$ The problem with this explanation is that it suggests that "potential energy" is just an artificial contrivance we invented to make the law of conservation of energy true. But that's not the case - the law of conservation of energy places significant constraints on the structure and behavior of the gravitational field (and the electromagnetic fields, for that matter), and it imposes more general constraints on physics via Noether's theorem. Potential energy arises from those fields, not from the law of conservation of energy itself. $\endgroup$– KevinOct 11, 2021 at 23:04
-
$\begingroup$ @Kevin That is all irrelevant to the question that was asked. The question was "Why is it called Potential Energy". The answer to that is that it is because the block has the potential to give (or create, depending on the perspective) energy. The energy is not in the block. $\endgroup$– OpifexOct 12, 2021 at 7:33
-
1$\begingroup$ "The block in itself has no energy." .... in the parlance of thermodynamics, this isn't strictly true. If the block is a system, then it has its internal energy (deltaU). The change to this is related by the "laws" of thermodynamics. In particular, the 1st law indicates that the change in internal energy of a system is equal to (all) the work done on (or by) the system plus (all) the heat added to (or given off from) it. Therefore, in the parlance of thermodynamics, the internal energy of the block system as it is raised in a constant gravitational field is increased by mgh. $\endgroup$– scottbOct 12, 2021 at 21:37
-
$\begingroup$ @scottb That isn't relevant to the question at all. Everything has thermal energy. But that is totally unrelated to the potential energy a block has when it's raised. $\endgroup$– OpifexOct 12, 2021 at 22:51
-
$\begingroup$ @Opifex: The comment was not directed at the question. It was a response to your statement "The block in itself has no energy" which was included as an attribution in my original comment. In the parlance of thermodynamics, "potential energy" is a subset of internal energy. $\endgroup$– scottbOct 13, 2021 at 13:49