# B Energy transfer (the very basics)

1. Sep 2, 2015

### Cliff Hanley

Q. When energy transfers from one form into another it is called ENERGY TRANSFER - eg, chemical to kinetic in a car, electrical to light in a lamp – but what is it called when energy leaves one object and enters another (eg, from a warm hand into a cold hand) but the energy doesn’t change from one form into another – as in the examples above, ie, when it is merely, in the 'hands' example, thermal energy leaving one object and entering another)?

Last edited by a moderator: Sep 3, 2015
2. Sep 2, 2015

### Cliff Hanley

When convection, conduction and radiation occur I am assuming that these are not examples of ENERGY TRANSFER given that the form of energy (thermal, ie, heat) is not changing into another form of energy but merely moving from object to object / substance to substance; am I correct in my assumption? Energy transfer is chemical to kinetic; electrical to light; kinetic to sound; GPE to kinetic; etc etc, yes?

Last edited by a moderator: Sep 3, 2015
3. Sep 2, 2015

### Cliff Hanley

From gcsescience.com;Some energy is changed into other forms and is wasted.”

Q. Is ‘wasted’ in this context a scientific term? I’m thinking of a light bulb lighting a room but most of the energy put in actually providing heat for the room. Yes, the primary purpose of the light bulb is to light the room but heating the room may be desirable to therefore the energy isn’t wasted, no?

Last edited by a moderator: Sep 3, 2015
4. Sep 2, 2015

### nasu

I don't think that in order to have "energy transfer" the energy has to change from one form to another.
Electrical energy is transferred from the power plant to our houses without changing into other forms, isn't it?

When thermal energy is transferred by conduction from a hot object to a colder one, it is usually called called "heat".
If the transfer is by conduction, it is just thermal energy all the way. You can have the transfer through radiation and then it it is first "transferred" to EM energy and then back to thermal energy.

5. Sep 3, 2015

### Cliff Hanley

Thanks. I know that electrical energy in our houses comes from the power plant but I don't know if "transferred" is the correct term for this. I'm only just starting to learn the basics; my question came from reading the following on gcse.science.com;

"We say that energy is transferred when one form of energy is changed into another form."

This made me wonder if there is another term for energy going from one place / object / substance to another without the energy changing form? Energy flow perhaps? Or energy exchange?

6. Sep 3, 2015

### Drakkith

Staff Emeritus
I believe that energy transfer is literally the transfer of energy from one place to another (or one object to another). Energy may or may not change form during this process.

No, convection, conduction, and radiation do indeed transfer energy. I think the term you're looking for is 'converted'. Energy is converted from one form to another, but it is transferred from place to place.

It really all depends on the context. My dad used a light bulb in the dog houses out back to keep the dogs warm, so all that energy being emitted as non-visible light certainly wasn't wasted. The gcsescience statement is referring to the fact that no machine is perfectly efficient. All machines will have some amount of energy that they use that isn't used for useful work. Clever construction or use can recover some of this wasted energy, but never all.

I don't like that statement. Energy can be changed from one form to another during transfer, but it doesn't have to be. The energy coming out of a generator at a power station is electrical energy. That same type of energy is transferred all the way to your house and used as electrical energy.

7. Sep 4, 2015

### Cliff Hanley

“I don't like that statement. Energy can be changed from one form to another during transfer, but it doesn't have to be. The energy coming out of a generator at a power station is electrical energy. That same type of energy is transferred all the way to your house and used as electrical energy.”

Thanks. Wiki* seems to agree with you (there is a page for energy transfer, another for energy transformation aka energy conversion). I am enjoying the gcsescience.com site but it’s troubling that they could get something so basic wrong.

“No, convection, conduction, and radiation do indeed transfer energy. I think the term you're looking for is 'converted'. Energy is converted from one form to another, but it is transferred from place to place.”

Re Wiki describing it as energy transformation *or* energy conversion; isn’t there a standard for these terms just as there is a standard for units of measurement etc (SI units)?

“It really all depends on the context. My dad used a light bulb in the dog houses out back to keep the dogs warm, so all that energy being emitted as non-visible light certainly wasn't wasted.”

By ‘non-visible light’ do you mean infra-red radiation? Is all of the em spectrum light? But only the roygbiv part is visible to us?

*Here’s the opening few lines to the aforementioned Wiki page on ENERGY TRANSFER;

“In the physical sciences, an energy transfer or 'energy exchange' from one system to another is said to occur when an amount of energy crosses the boundary between them, thus increasing the energy content of one system while decreasing the energy content of the other system by the same amount. The transfer is characterized by the quantity of energy transferred, which can be specified in energy units such as the joule (J), in combination with the direction of the transfer, which can be specified as in (to) or out of (from) one system or the other. The transfer occurs in a process which changes the state of each system.”

Thanks for such a comprehensive reply.

8. Sep 4, 2015

### Drakkith

Staff Emeritus
I don't think so, as those are common words, not scientific measurements.

Yes, I meant the rest of the EM spectrum, but primarily infrared light. Light usually refers to visible light, but it is sometimes used in other ways.

9. Sep 4, 2015

### Cliff Hanley

Thanks. Just to clarify; radio waves, microwaves, gamma rays, x-rays etc etc are all light? If so, em radiation = light; light = em radiation?

10. Sep 4, 2015

### Drakkith

Staff Emeritus
Eh, I'd say just use light to refer to the visible part of the EM spectrum to avoid confusion.

11. Sep 4, 2015

### Philip Wood

The conversion vs. transfer debate is not new...

Some years ago In the UK there was a backlash from Physics educators (mainly pre-university) against excessive emphasis on conversion of energy from one form to another. The gist of the argument was that energy is a calculated quantity and is conserved; there is no metamorphosis of this calculated quantity when, say, a ball is thrown upwards.

In some respects this backlash was healthy: there had been a tendency to encourage young students to classify energy along the lines: Look – there's a moving car; what sort of energy has it got? Look, it's climbing a hill; what energy conversion is taking place? I recall that Feynman (in 'Surely you're joking Mr Feynman?') inveighed against this sort of thing, pointing out that it taught no useful Physics. Putting in my own opinion, another thing this 'energy conversion' approach played down (to students' detriment) was the relationship between energy and work.

The backlash against 'energy conversion' and energy classification was sometimes taken to silly extremes. For example textbook writers made statements like "don't talk about heat, talk instead about heating". So you were supposed to say energy transferred by heating. [I have a brilliant idea: let's invent a single word to mean energy transferred by heating!] Another consequence was that many teachers avoid the term 'energy conversion', speaking of 'energy transfer', even in cases which they would previously have called energy conversion. I'm not sure whether rigorous adherence to this rule is actually useful.

Last edited: Sep 4, 2015
12. Sep 4, 2015

### Cliff Hanley

“...energy is a calculated quantity and is conserved; there is no metamorphosis of this calculated quantity when, say, a ball is thrown upwards.”

So the idea of a person throwing a ball upwards as chemical energy converting to KE to GPE to KE to EPE to KE to GPE etc etc is questionable?

“Another consequence was that many teachers avoid the term 'energy conversion', speaking of 'energy transfer', even in cases which they would previously have called energy conversion.”

But do they still use 'transfer' to describe energy moving from one object to another even when there is no change in the form of the energy. And why do you think gcsescience.com describe energy transfer only in terms of energy changing form?

13. Sep 4, 2015

### Philip Wood

Questionable? Perhaps. Wrong? I wouldn't say so. We know what we mean. We're not likely to get our calculations wrong (are we?) as a result of using this terminology? An extreme adherent of the "Energy is a calculated quantity and doesn't change" school might well object. A less extreme adherent might urge that you soften "converting" to "transferring".
Can't see why anyone would object to this.
What do they use for transfers of energy from one body to another, say in a head-on elastic collision between a moving sphere and a stationary sphere of equal mass, when the first stops and the second moves off with the same speed as the initial speed of the first?

Last edited: Sep 4, 2015
14. Sep 4, 2015

### Philip Wood

Just a footnote… In an effort to acknowledge the "energy is a calculated quantity" approach, I've been known to talk of energy 'changing category'. My idea here is to suggest that it's not the energy changing but the way we like to classify it. I don't kid myself that this really solves the problem – if there is one.

15. Sep 4, 2015

### Drakkith

Staff Emeritus
It's only questionable if you think of energy as some mystical substance and not simply as a useful quantity to make predictions with. There are plenty of applications where thinking of energy as being 'converted' to and from potential energy is extremely useful.

16. Sep 5, 2015

### Staff: Mentor

References to third party personal communications have been deleted and this thread is closed.