Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What is energy?

  1. Nov 3, 2015 #1
    Is it a particle, or not? My Chemistry teacher has been saying both and I am not sure which it is. Sometimes he says that energy is a particle, while sometimes, it is just a wave moving through particles.

    Thanks very much.
  2. jcsd
  3. Nov 4, 2015 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    It is neither. It is a property exhibited by both particles and fields. This property has turned out to be very useful in descriptions of how nature works.
  4. Nov 4, 2015 #3


    User Avatar

    Staff: Mentor

    I encourage you to take a look at what Richard Feynman had to say about energy in his Feynman lectures: What is energy?
  5. Nov 4, 2015 #4
    Thank you
  6. Nov 8, 2015 #5
    Often I have heard energy defined as, "the ability to do work".
  7. Nov 8, 2015 #6


    User Avatar

    Staff: Mentor

    Sounds to me like your teacher is talking about light, not energy.
  8. Nov 9, 2015 #7

    James Pelezo

    User Avatar
    Gold Member

    Energy is the language of the universe by which physical or chemical change is revealed. It is by its very nature the by product of an event that can be measured and interpreted as an indicator that change has occurred within the system of interest. The changes that occur within the object of interest, reveal themselves in the form of heat flow, propagation of electromagnetic radiation, movement of electric charge, nuclear radiation, movement of objects under the influence of an applied force. By choosing a relative point of origin and establishing a conduit of energy flow into a device able to detect and measure the energy's presence, one can determine what the system of interest is doing to adsorb or release a quantity of energy. If you are studying atomic structure, for example, by electrically or heat stimulating atoms, you will find the substance of interest will emit a characteristic color that when observed through a diffraction grating will reveal discrete lines of color at very specific wavelengths of light that are referred to in terms of discrete wavelengths. The question 'What causes these bright line discrete bands' led Niels Bohr to postulate the Concentric Ring Model of atomic structure. The bands have a wave-particle duality that can be translated into quantities of electromagnetic radiation with specific energy content and referred to as quantum photons. The light bands being observed are signals sent from atomic structures that have been interpreted as being a result of 'excited' electrons traversing from high energy levels of the electronic orbital configuration to lower energy levels of the electronic orbital configuration. Being that the bands are discrete, the consensus conclusion is the electrons associated with an atom reside in orbitals located at discrete distances from the atomic nucleus and orbit the nucleus much like planets orbit the sun. This postulate of the Bohr Model has been revised by further studies of the energy relationships with atomic structure and has lead to the Modern Quantum Model of the atom based upon quantum number sets that describe the behavior of an electron's behavior in terms of an energy window that keeps other electrons from colliding with their neighboring electrons. This is but one of many uses of energy as a scientific language used by the scientific community reveal, study and understand the complexities of our universe.
  9. Nov 9, 2015 #8
    This is the absolute value of energy in particle and electromagnetic wave alike.
    The first law of thermodynamics does not hinder all possible energy conversion of both wave and particle. Both have magnitude of energy and both could be converted reversible any time, by definition of the 1st itself as the law is just the accounting of the absolute value of energy (where it goes, where its from). It can not be created or destroyed. This simply means any processes cost you something as losses in a form of heat and light, so if you are going to reverse the process, you will spent a lot more than what you get.

    Consider burning 2H + 1/2O2 for instance releases heat (some goes to work, some as heat loss) and formed H2O as an end product, now if you are going to separate H2O once again, you would find out that the energy you'll spent on the separation will be much more than what you get in combustion.

    As of the moment (as there are no known knowledge or laws that energy cycles itself at the end point), nature limits reversible conversion and brings forth the 2nd law of Thermodynamics and it says energy conversion to some point is a one way street. Real world process is a one direction and there is what you call entropy production to any process above zero absolute pressure and temperature.

    Say for example, you use gasoline to run your bike on the street, but say, if you push your bike or have it pulled by a car or truck - it can not simply produce the gasoline you spent no matter what (so it's irreversible).

    Another example is you burn a gas and produce light and heat on the process, but given light and heat, you can not simply recover the gas.

    46d9fd53de36a1fc22d818633b0b18b9.png this is a simple equation but looking and focusing on it brings a lot of insights and tangents.
    Last edited: Nov 9, 2015
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook