# Force What is energy's role?

1. Jun 16, 2012

### Momento

Hallo,

When force is acted upon a certain object it could change its direction,movement. Does force require energy to be produced?

Looking at all the natural forces they seem to be created and force comes along with them. If force can move an object or stop an object or ever accelerate one. What is energy's role in all of them? Is it like this example:

Magnetic fields producing a natural force that can only be triggered by energy, same as gravity.

Are natural force only triggered by energy?

2. Jun 16, 2012

### Drakkith

Staff Emeritus
Re: Force...

The short answer is no, but it is kind of a complicated question.

I think you have a misunderstanding of what energy is. Energy is simply the ability for one system to perform work on another. Energy does not cause things to happen, that is the result of forces.

3. Jun 16, 2012

### haruspex

Re: Force...

The key word is could. If it does not in fact change anything, no work has been done. Work = force * distance through which the force produced movement of the point of application, in the direction of the force.

4. Jun 17, 2012

### Momento

Re: Force...

If force is produced over a distance is there energy being stored/converted...?

So force is crucial for a system to do work right?

5. Jun 17, 2012

### sophiecentaur

Re: Force...

In as far as it's included in the definition, you can't have one without the other.
If the car's not in gear (to transmit a force), the engine can't do any work in getting it moving.

6. Jun 17, 2012

### haruspex

Re: Force...

That doesn't logically follow. I stated how a force does work. Perhaps things other than forces can do work. Heat flow, e.g.

7. Jun 17, 2012

### sophiecentaur

Re: Force...

Nope. 'Work' is a strictly defined quantity, involving force and displacement. You are trying to associate work with energy in general, which is not precise.

8. Jun 17, 2012

### haruspex

Re: Force...

That's not universal. Many authorities distinguish between mechanical work, electrical work, chemical work and thermodynamic work (heat).

9. Jun 17, 2012

### sophiecentaur

Re: Force...

That's not how I am used to it. Do you have a reference to these other uses of the word? There seems little point in expanding its meaning so that it becomes synonymous with 'Energy' or 'Potential'.
I do know that 'work function' is used in respect of the energy required to remove photo-electrons but even that involves a mechanical idea, albeit small scale. (And it is a fairly ancient concept along with Electro Motive Force)

10. Jun 17, 2012

### DrewD

Re: Force...

I am far from an authority, but I have never heard heat referred to as thermodynamic work. In fact, the two are strictly different according to the first law of thermodynamics. Electrical work is the work done on a charged particle by the electric field. A charged particle feels a force in an electric field.
These specific cases of work can be distinguished, but the definition of work requires a force. If you don't explicitly define a force, it follows from the definition that $-\frac{dW}{dr}=F$.
I would be surprised to see work used in a situation where a force could not be easily defined unless the author was explicitly being loose with definitions.

11. Jun 17, 2012

### haruspex

Re: Force...

It's not so much a matter of expanding the meaning. It's more that the meaning of the word "work" has tended to contract to cover only mechanical work in most usage. It's a bit like the use of "forensic" to mean specifically forensic science. It really means "pertaining to law".
Early statements of the laws of thermodynamics included "heat is work and work is heat". The term energy was not so widespread.
But I was wrong to say thermodynamic work meant heat - it's everything except heat. For the rest, see http://en.wikipedia.org/wiki/Work_(thermodynamics).

12. Jun 18, 2012

### Momento

Re: Force...

Ok, Some of you are realting work to energy and I doubt their the same. I'm kinda confused and stuck in the middle here...

All I know now is a system that is able to work will always require "Force" to do so. In many system their are countless forces that have to come into account. Some forces are already being generated from a system's energy and other may have forces upon them such as you and I and all objects that have gravitational force on them.

"sophiecentaur" has a good point about the matter so far.

13. Jun 18, 2012

### Momento

Re: Force...

But isn't heat energy from its origins? I mean heat is the act of atoms having a lot of movement isn't it, so thats energy right?

14. Jun 18, 2012

### DrStupid

Re: Force...

Heat and work are exchange of energy.

15. Jun 18, 2012

### haruspex

Re: Force...

If you only consider work to cover mechanical work then, yes, force will be required.
The references I've found show that 'work' nowadays means any form of energy other than heat, and that if you care about the specific form of work then you should qualify it as mechanical, chemical, electrical, and so on.
For some of these it is not so clear that there would always be a force involved in transfer. Is there a force involved when a photon excites an electron in an atom? Maybe.

16. Jun 18, 2012

### Drakkith

Staff Emeritus
Re: Force...

The interaction by which any transfer of energy takes place is the result of a force. Without a force there would be no interaction between two particles and no energy would be exchanged.

17. Jun 18, 2012

Re: Force...

I would say force is a result of interaction not the other way around.

18. Jun 19, 2012

### Momento

Re: Force...

Thank you! Thats what I've been looking for. Force is crucial in a system to convert energy from its orignal form to another. Thats why we mainly use the formula W = F x D...

I just need to know that force is the tool for energy to use to be able to do "work". Without it you would not be able to do anything with that energy. Hope I'm on the right page here.

19. Jun 19, 2012

### Momento

Re: Force...

Honestly doubt that.

20. Jun 19, 2012

### CWatters

Re: Force...

I think that even applies to electrical or chemical systems.

21. Jun 19, 2012

### Momento

Re: Force...

I think it would apply to all those system. However, heat is another different matter...

22. Jun 19, 2012

### sophiecentaur

Re: Force...

Flanders and Swann did a memorable rendition of this, way back.

23. Jun 19, 2012

### Drakkith

Staff Emeritus
Re: Force...

Well, I would say that energy doesn't do work at all. Forces do work and a change is incurred in the system. Energy is simply a measure of how much work something can do.

24. Jun 19, 2012

### Nano-Passion

Re: Force...

I think it is a pointless distinction. Let us forget about force fields so we can separate force and energy from each other. Now if I throw a ball in space, we have something called kinetic energy and that energy can do work on object B when it is in contact.

But you could just as easily say that it is the force that did work by the equation F=ma. I accelerated mass A and it hits object B with force F and does work.

So which one is the "culprit"?

25. Jun 19, 2012

### Drakkith

Staff Emeritus
Re: Force...

The work done is going to depend on all the properties of an object, from it's mass to it's velocity to whichever forces it interacts by. (Along with the same things for the object it interacts with)

But if one were to choose which one does the work I would say it is the force. If two particles don't interact by a force at all, then they cannot perform work on each other. But then would the particles still have energy, at least with respect to one another? I don't know.