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B Energy, What Is It?

  1. Jul 8, 2018 #1
    I have a simple two-part question, or two simple questions.
    1. What is energy?
    2. What is charge?

    The charge I'm referring to is the charge on charged subatomic particles. And atom's charge is defined by the number of electrons and protons present in it. But an electron itself is called a negatively charged particle. We've studied about charge on an electron, so what is that?

    The positivity and negativity may come analogy for analogous purpose from Rutherford's experiments. That's not the point. The charge on an electron is 1.602e-19 C. What is that and what does it mean? And what causes it? Even if it means the electric field, what is it that causes that? What is this charge? I'm thinking the most common answer would be energy but even neutron has energy, it has to have energy.

    I would also like to know more about neutron. Neutron may be neutral in terms of charge and may be inseparable from proton but it must also contain some energy. I have never seen anyone account for the energy contained in the neutron while doing any calculation, neither have I ever seen anyone talk about it. And what happens to and with the energy of a neutron?
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  3. Jul 8, 2018 #2


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    You seem to have the misconception that charge and energy has "to be something". They are properties that we use to describe different aspects of physics. Science will not give you a deeper truth than that, it is about describing how Nature behaves in terms of observable effects, not about finding out what something "really is". I could give you the exact mathematical definition of what we mean in our models when we say things such as energy and charge, but I doubt that this is what you are looking for.

    Energy is not a thing. It is a property possessed by many objects that is useful in descriptions of Nature because, as far as we can tell, it is conserved.
  4. Jul 8, 2018 #3


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    Energy is the conserved quantity associated with time translation invariance (the laws of physics don’t change from today to tomorrow). Charge is the conserved quantity associated with gauge invariance (that one is more mathematical).

  5. Jul 8, 2018 #4
    Your credentials will back up your statements but how can a property/characteristic be expelled and be calculable? What do we mean when we say "release of energy"? Yes, it does happen in the form of matter in most cases like heat, which is defined as the particles in vigorous motion but we do calculate the amount of energy and we do put numbers before joule. What does that number signify? The appropriate way to put release of energy should be breakdown and separation of particles. I know that science is the study of nature and how it behaves but it has morphed into something more, it has taken the form of something transcendental, or been made so by people these days.

    Science confuses me a lot and I appear to be standing on the same platform again. Light has the ability to behave like a wave, it's wave like behavior is a physical property. Characteristics are possessions of physical manifestation like particles. So despite being capable of behaving like a wave, light has to be composed of particles. But light is described to not only have the characteristics of a wave but presented as if it is wave. What is a wave? From what I know, wave can only be defined as the movement of particles, mostly where they propagate back and forth following a curvature but that is not necessary. People give examples by showing water waves but that is formed by and due to the presence of particles. Water waves involve particles and so do sound waves. For light, the only thing I remember reading in context of light is that it is a mean/medium of transfer and transportation of energy. This has left me confused and befuddled.
  6. Jul 8, 2018 #5
    I read that and I could not understand a single thing after the briefing. But Physics Girl said that energy is not always conserved and that some energy was lost when a light signal was received from very far away. I think she has a doctorate in physics. Now, the lost energy could simply have been lost in space but given that it came from someone with a PhD, it is something to think about. What do you think that was all about?
  7. Jul 8, 2018 #6


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    Umm, I have a PhD too, so I am not sure what your point is.

    You will have to ask Physics Girl what she meant. However, on cosmological scales the universe is not time translation invariant, so energy is not conserved on those scales and indeed it is difficult to define what the energy of the universe is.
  8. Jul 8, 2018 #7
    No point. But I'll make a case now. You both are accomplished geniuses so shouldn't this clash of thoughts be politely discussed in a civil manner?

    What does time translation invariant mean? How would you explain it to a kid? I am not smart so give it a try please. Speaking of energy conservation, what happens with the neutrons and the energy within them? Why do they even exist? I have read that it's to provide stability to the atoms and to keep the protons together without scattering. And they also account for the mass of the atom (surprisingly, not for the energy, never for the energy). It appears that neutrons consist of both electrons and protons but I don't think that is the case. And even electrons and protons are nothing but two things which have been named in an analogous way based on their behavior and interaction with one another. But if I were to consider that (that neutrons don't have electrons in them), then why is it that the electrons don't reside within the nucleus and simply combine with the protons since they do attract one another? But on the other hand, if I were to consider that they have electrons in them, then it would also mean that they have protons in them too which negate the charge of one another to make the neutron neutral in nature in which case, it still remains the same meaning that the electrons and protons should still come together. Speaking of which, do these atomic and subatomic particles have a shape? And if they are spherical, what is between the space where two adjoining particles? If nothing, then how could there not be nothing? Absence of something can be characterized by reference of something existential's presence but if there simply is nothing, well how would we know that and how is that even possible? I guess it's much harder to ask this question than it might be to answer it.
    Last edited: Jul 8, 2018
  9. Jul 8, 2018 #8


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    Since you haven't provided a source, we have to guess. But it does sound very much like the person was talking about light travelling in an expanding universe and redshifting = losing energy. This is expected.
    Without going into any detail, the Noether's theorem mentioned earlier explains how various conservation laws arise if certain conditions are met. In everyday and local realities, where 'local' includes everything up to a scale of galactic clusters, the conditions are such that there is a property we call energy, which is conserved in closed systems.
    On larger scales, including the scale of the universe, where those conditions no longer hold in general (for various technical reasons that have to do with space-time shape and changes) - there is no conservation of energy, so it can change in one place (light redshifting) without a corresponding change somewhere else.

    Try this video from 23:00 to about 30:00, and see if it explains the accounting role of energy.

    Also, a few pointers:
    - I think it would be best to focus on one topic first, and understanding it to one's satisfaction, before jumping to different ones, like charge or wave nature of light.
    - If you find the answers so far unsatisfactory, try and provide an example of an answer to a 'what is X' question that you're looking for.
  10. Jul 8, 2018 #9


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    I am not sure that there is a clash of thoughts. But if she wishes to join the discussion then I am sure it will be civil.

    In general it means that the physical laws which govern the system are the same at different moments of time. In the case of general relativity it specifically means that the shape of spacetime must be constant over time. An expanding universe is therefore not time translation invariant.

    The energy in the neutron remains in the neutron until some or all of it is released in a nuclear reaction.

    These questions are the subject of several different threads. Please keep your focus on the questions in your original post. It adds a high level of confusion to the forum when threads wander dramatically away from the topic of the original post.

    Also, if you choose to make new threads for any of these questions, please put a little more thought and effort into asking the question. A stream of consciousness might feel cathartic but it is unlikely to garner any useful replies.
    Last edited: Jul 8, 2018
  11. Jul 8, 2018 #10


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    A simple explanation is that some change has occurred in a system and this change causes other changes which propagate outwards and away from our original system. A 'system' could be just about anything. It could be a lightbulb, a single atom, an entire planet, etc.

    The way these changes propagate outwards depends on the exact situation. When a light bulb releases light, a process in the filament causes a change in the surrounding electromagnetic field. Because of the details of how the EM field behaves, this change in the field moves outward and away from the light bulb. When this change in the field reaches a charged particle it causes that particle to move. Since the particle has moved, work has been performed on it by the field.

    All of that reworded: energy is radiated outwards from a lightbulb and is absorbed by a charged particle.

    Using 'energy' has allowed me to condense the former paragraph into a single short sentence. Note that I don't have to use the term 'energy'. Physics would be just fine if no one had ever invented that word, but it would make things more wordy and more difficult to work with in some circumstances. One could argue that energy is nothing more than a name used to shorten things. But that's true for almost all quantities. I could say the same thing for 'momentum' and 'velocity'. Both of these terms help us describe movement in a short, compact form, including the math. Most of these words can be written as single terms in a mathematical equation instead of having to use multiple terms and/or equations to describe the same thing.

    In fact, one could argue that the process of substituting a more complicated part of an equation with a single term is what gave rise to most of the quantities.
  12. Jul 8, 2018 #11


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    No it's not. Heat is the transfer of thermal energy.

    Most of this you are just making way too complicated and your thoughts are way too scattered for it to be likely you will make sense of it. Pick one manifestation of energy and focus on fully understanding that before moving on to the next thing. How about we discuss a 1kg rock dropped from a height of 1 meter?
  13. Jul 8, 2018 #12


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    I'd like to tack onto Russ's post with the suggestion that if you want to really know what energy is, then you must dig into some basic math involving it. It would then be much easier to understand what is meant when we say that energy is a conserved quantity and what I meant in my earlier post. It would be a bit like trying to learn biology without learning what cells are.
  14. Jul 8, 2018 #13
    This doesn't sound that hard. It's basically what I studied in the very first physics lesson. I've heard this on numerous occasion, but what is the universe expanding into? There must be container. And if there is one, would it not one day hit the boundary and burst due to all the pressure and still be confined within the boundary of the container? Could it be that there may be a limit but scientists have yet to reach and find that? And intuitively speaking, expansion usually implies growth, growth in size, which usually signifies increase in matter. By that logic, all the laws of conservation don't seem to be applicable anymore.

    But how could it be a quantifiable and measurable? Any physical property is measurable but the property relating to and used as a synonym for characteristic can't be measured as it is a qualitative property and not quantitative. How honest is someone? Very, or a 100%. But to answer that in terms of percentage or any other form, you would run an experiment and ask questions, which is quantitative. 10 questions and 10 correct answers mean 100%. But this only works when you have something else to refer to. The quality is quantified with respect to some other quantity (and may be a subject to change but let's assume that it's not) and it is only a representation of the individual's adherence to honesty in a confined environment with limitations and known values, which in this case are the questions and the answers.

    And what is thermal energy?

    And I apologize for that. I suppose the question above is somewhat related. We definitely can start with a rock being dropped to the ground but go easy on me as I'm only a high school graduate. I want to get my concepts cleared up before joining college.

    I think this was it.

    My sincere apologies but I was afraid that making more threads would make it more disorganized. But I started on that neutron question with a related topic - energy of neutrons but got derailed because I've had these questions for a long time but never asked. I think science may not for me. I apologize for wasting all of your time.
  15. Jul 8, 2018 #14


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    Energy is not conserved on cosmological scales. Photons have less energy when they arrive here than they did when they left points billions of light years away. It doesn't get "lost is space" it simply stops existing.

  16. Jul 8, 2018 #15


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    This is a topic for a different thread, in the cosmology section.

    Has your question regarding energy been sufficiently addressed? If so, then you might collect your thoughts, decide on the next most pressing question in your mind, and start a new thread. Just be sure to put as much effort into asking a good question as you hope for people to put into answering. It will pay off in the end, with higher quality answers.
  17. Jul 8, 2018 #16


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    Rock first.
    That's fine. This is high school level stuff.

    Work is force times distance. Energy is the capacity to do work. So a 1kg (10N) rock 1m off the ground has potential energy: PE=F*D=10×1=10 Joules

    What does this number MEAN? What can we do with it? All it is is a useful number that scientists have noticed is conserved and can be converted between different forms.

    Good so far?

    So now you drop the rock...
  18. Jul 8, 2018 #17
    This feels exactly like school, studying formulas and solving equations just to pass my exams. I understand what you've written, but I don't really understand it. I know the formulas and the relations but it's still not clear to me. Does it mean that the rock has the potential to transfer it's energy and do work which requires 10 joules worth of energy? But this doesn't explain what energy is! And a few more questions. Why doesn't the rock's energy dissipate into the air and the surrounding? It will be applying force to the air particles so it must be doing some work. So does it not lose any energy? I'm sorry for prolonging this but I'm not doing it deliberately. I genuinely don't understand this.
  19. Jul 8, 2018 #18


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  20. Jul 8, 2018 #19


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    The rock does work on the ground that stops it, and the exact amount is closer to 9.8 joules. A 1 Kg rock weighs 9.8 Newtons. @russ_waters was just using an approximation to make the calculations easier.

    Sure, but the amount of energy lost to air resistance by a rock falling 1 meter is minuscule. If it were falling from a much greater height, this energy loss would be significant.

    As @Orodruin said in post #2:
  21. Jul 8, 2018 #20


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    Yes it does. You're not satisfied because you think there should be some deeper meaning, but there isn't. Physics, in principle, is really simple: it is just a collection of numerical relationships between phenomena. There is no "meaning" beyond that.
    Maybe I shouldn't have mentioned step 2. Step 1 is just you holding the rock at an elevation of 1m. Are you ok with what that means? Are these all questions about as fter you drop it?
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