Understanding the Basics of Energy

[James A. Putnam]

Drakkith,

Sorry, don't know what interrupted my reponse. Energy is defined as force times distance. That effect can occur in internal or external circumstances. For instance, a collection of gas molecules in thermal equilibrium all have energy. If those molecules are allowed to do that which they do when they are freed, they will push against a piston and perform work which is the product of their force times the distance the piston moves. I know you know this. Energy is not the cause in either circumstance. Force is the cause. The fundamental question is: What is force?

No I don't have a reference. Have you ever seen an introductory physics text that does not distinguish between internal energy that does nothing more than exist and internal energy that is put into circumstances where it might result in pushing something so that we may differentiate between energy that has produced work and energy that just exists?

James

 

[Dale]

Your crystal clear is no answer to: What is energy?

When someone asks "What is X" then the answer is the definition of the word "X". Energy is defined as the capacity to do work, so when someone asks "What is energy" the answer is the capacity to do work.

 

[Dale]

Energy is defined as force times distance.

No, it is not. For example, consider kinetic energy. An object of mass m moving at a constant velocity v has 0 force, so force times distance is also 0, but it has a kinetic energy of 1/2 mv², which is non-zero. Therefore energy is not force times distance. Work is force times distance, energy is the capacity to do work. The moving object may collide with some other object and exert a force over a distance, so the moving object has the capacity to do work even if it is not currently doing work.

 

[KingNothing]

If you ask my crazy ex-girlfriend, she'll tell you it's the feeling you get when you have Jesus in your soul!

 

[James A. Putnam]

Dale Spam,

"An object of mass m moving at a constant velocity v has 0 force, so force times distance is also 0, but it has a kinetic energy of 1/2 mv², which is non-zero. Therefore energy is not force times distance."

No that is not correct. It is true that an object moving at a constant velocity has something theorists call kinetic energy. However, that energy attrributed to it is the result of a calculation of force times distance. The sum total is called energy even though it is no longer experiencing force times distance. However, the loose use of the word energy does not relieve it of its definition. There is no other definition of energy other than force times distance. There are circumstances where the word energy is applied as if it is potential, that condition is a theoretical decision. The empirical circumstance is that energy is force times distance. The question remains: What is force? I don't see answers for that question. Force is skipped over.

Energy is a name applied to results of force times distance. The use of the name energy for any object that is not undergoing acceleration is a substitute for the long answer. The long answer has to do with the amount of force times distance that that object can exert later if it is allowed to do so.

James

 

[Drakkith]

Force:

In physics, a force is any influence that causes a free body to undergo a change in speed, a change in direction, or a change in shape.

 

[Dale]

There is no other definition of energy other than force times distance.

No, all of these define energy the way I have suggested:
http://www.bios.niu.edu/meserve/bios106/Outline.Lect5.Bios106.pdf
http://flightline.highline.edu/wmoses/EnvScience/LectureNotes/PDF/Energy.pdf
http://www.physchem.co.za/OB12-mec/energy.htm
http://en.wikipedia.org/wiki/Energy
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
http://books.google.com/books?id=QB...esnum=6&ved=0CEUQ6AEwBTgK#v=onepage&q&f=false

Can you provide any credible reference for your definition?

 

[ZealScience]

But I think kinetic energy is also a potential to do work. Although energy follows from integral of forces, technically they are not pushing a force and act on a displacement, they just have potential to do work. Though the dot product is constant, the force and displacement are yet to be determine, if you aren't sure of any of the quantity how can you
define it using the two quantities?

 

[James A. Putnam]

"n physics, a force is any influence that causes a free body to undergo a change in speed, a change in direction, or a change in shape."

So I ask: What is force? In other words: What is cause? If the answers are givens that is fine so long as they are admitted to be unexplained givens.

James

 

[Drakkith]

"n physics, a force is any influence that causes a free body to undergo a change in speed, a change in direction, or a change in shape."

So I ask: What is force? In other words: What is cause? If the answers are givens that is fine so long as they are admitted to be unexplained givens.

James

Again, you are looking for philosophical answers. Nothing we can give you will satisfy you because science cannot give a philosophical answer.

 

[WannabeNewton]

IMO, if you want an answer that cannot be directly expressed mathematically you are asking for something that cannot be given by physics.

 

[ZealScience]

IMO, if you want an answer that cannot be directly expressed mathematically you are asking for something that cannot be given by physics.

But there got to be something that cannot be described by another mathematical quantity. Ifyou use one thing to describe another, what about that thing? If no quantity is given to describe the object, how can we use mathematics?

 

[James A. Putnam]

No, all of these define energy the way I have suggested:

These are not definitions. These are descriptions of what effects might be expected. I am asking about cause. Energy is not a cause.

"Can you provide any credible reference for your definition?"

Ok. From College Physics by Sears and Zemansky : "Work is done only when a force is exerted on a body while the body at the same time moves in such a way that the force has a component along the line of motion of its point of application."

What work is performed by an assemblage of gas molecules bouncing around that object?

 

[James A. Putnam]

"IMO, if you want an answer that cannot be directly expressed mathematically you are asking for something that cannot be given by physics."

Energy is expressed mathematically as fxd.

 

[WannabeNewton]

Yes energy can be expressed mathematically. My point is that you are asking for a definition of energy that is mainly philosophical and cannot be backed up by math.

 

[Drakkith]

But there got to be something that cannot be described by another mathematical quantity. Ifyou use one thing to describe another, what about that thing? If no quantity is given to describe the object, how can we use mathematics?

Umm, this question doesn't make any sense. First, everything can be described by mathematics. Second, we define everything in relation to other things. The most fundamental concepts in science would be meaningless without the other fundamentals.

 

[James A. Putnam]

"But there got to be something that cannot be described by another mathematical quantity. Ifyou use one thing to describe another, what about that thing? If no quantity is given to describe the object, how can we use mathematics?"

Cause is unknown and cannot be described by the use of mathematics. Only effects are observed and only effects are described by the use of mathematics. I have mentioned earlier in my posts that the causes included in physics equations are inventions. No one knows what is cause. It is these invented causes that separate theoretical physics from empirical evidence. The reason for inconclusive answers is that cause remains unknown. No matter how many names of possible causes have been invented and declared to be indefinable properties, they are substitutes for the unknown.

James

 

[Drakkith]

No, all of these define energy the way I have suggested:

These are not definitions. These are descriptions of what effects might be expected. I am asking about cause. Energy is not a cause.

"Can you provide any credible reference for your definition?"

Ok. From College Physics by Sears and Zemansky : "Work is done only when a force is exerted on a body while the body at the same time moves in such a way that the force has a component along the line of motion of its point of application."

What work is performed by an assemblage of gas molecules bouncing around that object?

Yes, they are definitions.

Your example isn't specific enough, but I'll try to answer you. If the gas is hotter than the object, work is done by the transfer of heat from the gas to the object. Also, is this object moving through the gas? If so, then work is being done on the gas itself. I'm not 100% sure, but maybe work is being done every time the gas bounces off of something else?

 

[ZealScience]

Umm, this question doesn't make any sense. First, everything can be described by mathematics. Second, we define everything in relation to other things. The most fundamental concepts in science would be meaningless without the other fundamentals.

But how do you define charges? If you define charge by current, then how to define current? Using charges? No.

If you define charges by string theory or superparticles or Higgs field, but how can you explain them? The only way I find is to use Anthropic Cosmological Principle.

Another example is principle of least action (Lagrangian mechanics). It is so powerful because it can define many theories. What about itself? How to derive it? Anthropic Cosmological Principle? Just like Euclidian geometry for instance, Euclid needs predisposition to define other postulates, they are fundamental.

 

[Dale]

From College Physics by Sears and Zemansky : "Work is done only when a force is exerted on a body while the body at the same time moves in such a way that the force has a component along the line of motion of its point of application."

That is a definition of work, not energy. Try again.

 

[James A. Putnam]

The point is that every molecule does 'work' but not useful work. Their end effect is no work. Your example: "If the gas is hotter than the object, work is done by the transfer of heat from the gas to the object." does not represent work. Heating an object is not an example of work.

James

 

[James A. Putnam]

"That is a definition of work, not energy. Try again." That quote from Sears Zemansky separated the macroscopic view of useful energy performing work from the microscopic world of energy that does not produce useful work. In thermodynamic entropy it is erroneously said that that entropy is a measure of energy no longer available to perform work. There is no separation of energy. Energy is force times distance. There is a academic separation between energy that performs useful functions and energy that is considered to act randomly.

James

 

[Drakkith]

"But there got to be something that cannot be described by another mathematical quantity. Ifyou use one thing to describe another, what about that thing? If no quantity is given to describe the object, how can we use mathematics?"

Cause is unknown and cannot be described by the use of mathematics. Only effects are observed and only effects are described by the use of mathematics. I have mentioned earlier in my posts that the causes included in physics equations are inventions. No one knows what is cause. It is these invented causes that separate theoretical physics from empirical evidence. The reason for inconclusive answers is that cause remains unknown. No matter how many names of possible causes have been invented and declared to be indefinable properties, they are substitutes for the unknown.

James

What? This is nonsense. Imagine a kid that constantly asks why. When do you stop asking why?

 

[ZealScience]

I am trying to ask how to describe fundamental theories mathematically here. Even mathematics itself needs fundamental predispositions that cannot be explained (sorry, I haven't learned Number Theory yet, there can be nonsense in my reply).

 

[ZealScience]

"But there got to be something that cannot be described by another mathematical quantity. Ifyou use one thing to describe another, what about that thing? If no quantity is given to describe the object, how can we use mathematics?"

Cause is unknown and cannot be described by the use of mathematics. Only effects are observed and only effects are described by the use of mathematics. I have mentioned earlier in my posts that the causes included in physics equations are inventions. No one knows what is cause. It is these invented causes that separate theoretical physics from empirical evidence. The reason for inconclusive answers is that cause remains unknown. No matter how many names of possible causes have been invented and declared to be indefinable properties, they are substitutes for the unknown.

James

Actually it is because of unknown causes, quantum mechanics was born. They are trying to explain these using fundamental theories (e.g Grand Unified Theory, String theory, etc).

The thing that I doubt is there might be a final theory that cannot be decribed by others but only Anthropic Cosmological Principle.

 

[Dale]

Energy is force times distance.

So find a credible source that states it. A university site, or textbook, or peer-reviewed paper, or anything else credible that actually says that energy is force times distance, not work.

 

[James A. Putnam]

"What? This is nonsense. Imagine a kid that constantly asks why. When do you stop asking why?"

Cute! The reason I press for answers is because it is very important for the fundamentals of physics to know these answers. Every guess that has served as a substitute for a real answer remains, even today, an obstacle to understanding the nature of the universe. Here is an example of a guess: Mass was made arbitrarily into an indefinable property simply because we did not know what else to do with it. Mass is linked in some important way to the concept of energy. We know neither what is energy nor what is mass. To pretend otherwise is not helpfull.

James

 

[Drakkith]

"What? This is nonsense. Imagine a kid that constantly asks why. When do you stop asking why?"

Cute! The reason I press for answers is because it is very important for the fundamentals of physics to know these answers. Every guess that has served as a substitute for a real answer remains, even today, an obstacle to understanding the nature of the universe. Here is an example of a guess: Mass was made arbitrarily into an indefinable property simply because we did not know what else to do with it. Mass is linked in some important way to the concept of energy. We know neither what is energy nor what is mass. To pretend otherwise is not helpfull.

James

And with this, the thread should end.

 

[James A. Putnam]

So that is the answer?

 

[Drakkith]

So that is the answer?

See one of the 50 previous posts.

 

[James A. Putnam]

I did.

 

[Drakkith]

I did.

I'm done. You cannot accept the answer in front of you and seem to want to make this into some philosiphical discussion. Science has defined energy and work and if you cannot accept those definitions then you should not be on Physics Forums.

 

[James A. Putnam]

"You cannot accept the answer in front of you and seem to want to make this into some philosiphical discussion. Science has defined energy and work and if you cannot accept those definitions then you should not be on Physics "

No I do not agree with your explanations. Is this final remark of yours intended to invite me to leave physics forums? If not, then what is its point?

James

 

[ZealScience]

Just one more: what about Higgs field and inertial mass? They are even mor difficult to define

 

[ZealScience]

"You cannot accept the answer in front of you and seem to want to make this into some philosiphical discussion. Science has defined energy and work and if you cannot accept those definitions then you should not be on Physics "

No I do not agree with your explanations. Is this final remark of yours intended to invite me to leave physics forums? If not, then what is its point?

James

But you are missing the point. Work and Energy is defined by people, it's clearly something that we know. If you say this is nonsense, then maybe you are talking about other concepts but not work and energy.