Talk:Q11379

Subsets:

renewable energy (Q12705): energy collected from renewable resources, mechanical energy (Q184550): potential and kinetic energy associated with the position and movement of a physical object, thermal energy (Q209233): internal energy present in a system due to its temperature, internal energy (Q180241): energy contained in a system, excluding energy due to its position as a body in external force fields or its overall motion and so on? form of energy (Q3935690)? --Fractaler (talk) 09:55, 19 September 2016 (UTC)

who says that energy is the same as mechanical work or heat?

These statements are both incorrect. Check an article about work or heat and you will see that they are quite different. Heat and work are only the amounts of energy *transferred* between *two* systems (thus increasing the energy of one sys & decreasing the energy of the other) in specific types of processes -- they are process functions (properties of a process) while the property energy itself is a state function (property of a specific system). They are not at all synonymous with the concept of energy itself. DavRosen (talk) 02:16, 29 January 2017 (UTC)

work, heat, and mass can serve as ways to measure energy

From english wikipedia: "In physics, energy is a property whose form can be converted, and whose quantity is transferred by work or heating, thus constituting a capacity limit on work or heat."

Thus one can use work or heat to measure energy because the energy limits the capacity to perform work or to perform heating.
For example you can use all the energy in an object to heat another object and measure its temperature change to determine the energy you've transferred.
Or you can use energy to lift an object against gravity (until all the energy is transferred) and use the displacement to determine the amount of energy you've transferred.

By mass-energy equivalence, all energy has mass, meaning that if you have a sensitive enough weighing scale you can measure the energy of any system simply by measuring its mass and multiplying by c^2 , so mass is a third way that one can measure energy. (Unfortunately, in practice, the mass of the typical amounts of energy we encounter in daily life are too small to measure with the scales we use in everyday life.)

DavRosen (talk) 02:29, 29 January 2017 (UTC)

Work and heat can be regarded as forms of energy, can't they? --Infovarius (talk) 16:04, 30 January 2017 (UTC)

Work and heat aren't forms of energy in the same sense as, say, kinetic or potential energies (except colloquially or loosely). Actually, they (very clearly for work but really for heat too) are ways of transferring energy, and as quantities they measure the amount of energy (of what ever form) that was transferred in such ways (by certain processes). They aren't additional forms of energy in themselves that would have to be included in a system's total energy -- in fact they aren't state functions so they aren't properties of a system at all. For example, it is incorrect and indeterminate to ask how much energy of the form "work" is present in an object or system. Work can't be converted into "another" form of energy, but rather it describes a type of transfer of energy, for example when one body acts on another with a force so as to transfer energy "as work" to it (perform work on it). The acting body loses energy (often some form of potential or kinetic energy but definitely not anything called "work energy") and the acted-on body gains the same amount of energy (which may or may not be in the same form as the energy that was lost by the other body). When people say "heat is a form of energy", they really mean "thermal energy is a form of energy", and even that concept is technically problematic as it is often ambiguous and unmeasurable -- "internal energy" is a somewhat different but more rigorous concept used in thermodynamics instead of "thermal energy" -- see the thermal energy article in english wikipedia. When people say "work energy" -- well mainly they don't but if they did they might mean mechanical energy, but this is misleading because in fact non-mechanical energy can do work as well, for example light reflecting off of an object can accelerate the object slightly, transferring some of the light's momentum and energy. You wouldn't want to say that the light "contained" some "work energy" before it hit the object -- in fact, under different circumstances the same light could have transferred all of its energy "as" heat (i.e. via a heating process) and none "as" work (i.e. by performing work). DavRosen (talk) 20:11, 30 January 2017 (UTC)