What is Energy? Exploring the Definition and Meaning of Energy

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In summary: I know that F=ma, where m is mass and a is acceleration, but mass is apparently equivalent to energy and therefore your definition of energy appears to me to be cyclical. ie E=maXcosa where m is actually in a sense E aswell.
  • #1
madness
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I have heard the definition of energy to be "capacity to do work". However, the term "work" to me seems even more ambiguous than the term "energy" itself. Does anyone have a good answer to the question of what energy actually is?
thanks
 
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  • #2
There is one thing you must understand first. Everybody learns in different ways. For some people, the capacity to do work is a good definition. For others, its not. Our minds all make sense out of things differently.

I learn best by example. A battery holds energy because once the energy is released, useful things can happen (running electronics). A ball held up in the air has potential energy because physical energy had to be used to raise it. Once it is dropped, that energy will be released again.

Energy is in many ways an abstract concept. We measure it by observing what it does, not the energy itself (for most purposes). We don't just go out and see energy. Energy does not have its own dimension. You may want to define it for yourself as an arbitrary measurement created simply to say that when you push a box up a hill, it comes back down the hill equally, or to say that when the fuel inside one of your car's cylinders explodes and releases energy, it pushes the car forward.
 
  • #3
energy is the ability of an object to do work
an object does work by appying force over a distance
so work is defiend by

[tex]w=FX \cos \alpha[/tex]

where
w - the amount of work done
F - the force the object applied over the distance X
X - the distance over which the force F was applied
and alpha is the angle between the direction of the applied force and the direction in which the object moved when the force was being applied.

when we say an object has x energy that means it has the ability to do x work

when object A does work on object B (and only on object B) then the work A has done is substracted from its energy and added to the energy of B.
 
  • #4
Go through Ch 4, Vol 1 of The Feynman Lecture on Physics.
 
  • #5
thanks for all the help. just one more thing. since your definition of energy uses the term force it would be helpful to have a precise definition for force aswell. I know that F=ma, where m is mass and a is acceleration, but mass is apparently equivalent to energy and therefore your definition of energy appears to me to be cyclical. ie E=maXcosa where m is actually in a sense E aswell.
I know I am most likely mistaken in this as I don't have a particularly advanced knowledge of physics but I would be interested in hearing your answers. thanks again
 
  • #6
mass is considered a very dense form of energy, but that's way, way beyond the realm of Newtonian mechanics, which the old F=ma is.
 
  • #7
madness said:
thanks for all the help. just one more thing. since your definition of energy uses the term force it would be helpful to have a precise definition for force aswell. I know that F=ma, where m is mass and a is acceleration, but mass is apparently equivalent to energy and therefore your definition of energy appears to me to be cyclical. ie E=maXcosa where m is actually in a sense E aswell.
I know I am most likely mistaken in this as I don't have a particularly advanced knowledge of physics but I would be interested in hearing your answers. thanks again

force is defiend to be any interaction between two objects
m in f=ma is what's called inertial mass
inertial mass is defiend to be the ability of a body to prevent a change in its acceleration that's the definition used no need to involve e=mc^2 :smile: .

einsteins infamous e=mc^2 simply states that matter can be converted into energy and energy can be converted into matter. (they aren't the same things one can just be converted to the other).
 

1. What is energy?

Energy is the ability to do work or cause change. It is a fundamental concept in physics and is found in various forms such as kinetic, potential, thermal, electrical, and chemical energy.

2. How is energy measured?

Energy is measured in joules (J). Other common units of measurement for energy include calories, kilowatt-hours (kWh), and British thermal units (BTUs).

3. What are the sources of energy?

The main sources of energy are fossil fuels such as coal, oil, and natural gas, as well as renewable sources such as solar, wind, hydro, and geothermal energy. Nuclear energy is also a significant source of energy.

4. How is energy converted from one form to another?

Energy can be converted from one form to another through various processes such as mechanical work, electricity generation, and chemical reactions. For example, a wind turbine converts wind energy into electrical energy.

5. What are some real-life examples of energy?

Some common examples of energy in daily life include the energy used to power vehicles, heat homes, and turn on lights. Other examples include the energy in food that we consume and the energy used by our bodies to perform physical tasks.

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