Law of Conservation of Energy of a wind turbine

[ElegantSir]

Homework Statement

"identify the type of energy conversions present in each of the following situations. Some questions may use multiple types of energy."

1) a wind turbine producing electricity
2) two children sliding down a hill on a toboggan
3) a toaster oven browning a bagel

Homework Equations

There are no equations for this, just definitions for different types of energy!

- elastic potential energy - kinetic energy - electrical energy
- chemical potential energy - sound energy - radiant energy
- nuclear potential energy - thermal energy - gravitational potential energy

The Attempt at a Solution

These are what I think the answers may be:

1) Kinetic to electrical energy
2) kinetic energy to thermal energy
3) electrical energy to thermal energy

Im not entirely sure if these answers are correct. It would be much appreciated if someone could help me identify the other types of energy I may be missing in my answers.

 

[teetar]

Don't take my word for these, but consider that in a real life situation for 1, there would be friction in the moving turbine, and in situation 2 the energy that is moving them down the slope is coming from somewhere.

I don't answer often, so hopefully I've not given too little or too much information in this response, and hopefully it helps. Cheers!

 

[andrewkirk]

In the toboggan case, there's another conversion prior to the one you describe. Where does the toboggan's kinetic energy come from?

Ah, I see teetar already mentioned this.

 

[ElegantSir]

Thanks for the responses, this is what I've came up with after the fact:

1) kinetic energy to electrical and thermal2) gravitational potential energy to kinetic and thermal energy3) electrical energy to radiant and thermal energy (Possibly chemical energy as well as the chemical composition of the bagel changes while it is being browned)

 

[CAT 2]

Sorry to resurrect this thread, but I have some problems with this question too. Is what ElegantSir is saying correct because I have come up with

1. kinetic energy of air to kinetic energy of turbine to electrical energy.

2. gravitational potential energy to kinetic energy

3. electrical energy to thermal energy (or is it chemical energy?)

If someone could help me out on these that would be great! Thanks.

 

[haruspex]

Sorry to resurrect this thread, but I have some problems with this question too. Is what ElegantSir is saying correct because I have come up with

1. kinetic energy of air to kinetic energy of turbine to electrical energy.

2. gravitational potential energy to kinetic energy

3. electrical energy to thermal energy (or is it chemical energy?)

If someone could help me out on these that would be great! Thanks.

For 1 and 2, as noted in earlier posts, there are losses, so they should be mentioned.
3 is a bit tricky. Yes, thermal energy. If any chemical energy is produced then, in principle, that could be harnessed. What are the resulting chemicals? Could energy be recovered from them?
Also, think about what happens to the moisture content.

 

[CAT 2]

Ok so:

1. kinetic energy of air to kinetic energy of turbine to electrical energy and thermal energy.

2. gravitational potential energy to kinetic energy and thermal energy.

3. electrical energy to thermal energy and chemical energy.

From looking at the above posts, thermal energy seems to be the one that was missing from the first two. I want to understand why this is, is it because everything is composed of/ has particles moving around in it and therefore everything has thermal energy?

 

[haruspex]

and chemical energy.

You have not addressed my objections to listing chemical energy, nor considered moisture changes.

is it because everything is composed of/ has particles moving around in it and therefore everything has thermal energy?

Thermal energy can be listed because no conversion is 100% efficient. There is is always some friction, or resistance in electrical cables, etc., though whether the question expects you to worry about that I am not sure.

 

[CAT 2]

3 is a bit tricky. Yes, thermal energy. If any chemical energy is produced then, in principle, that could be harnessed. What are the resulting chemicals? Could energy be recovered from them?

Radiant energy should be added as that is how the toast ends up browned, by infrared rays.
Couldn't our bodies harness the chemical energy as it breaks down the food, and turns it into other kinds of energies? Also doesn't the toaster cause the Maillard reaction, isn't that chemical change, or is it just chemical change that is not producing chemical energy? ( < probably). I don't really know any other way this could be chemical in the toasting process. It sounds like I shouldn't have it in at all.

3. Electrical to radiant and thermal energy. Is that better?

 

[haruspex]

Radiant energy should be added as that is how the toast ends up browned, by infrared rays.

Excellent point.

Couldn't our bodies harness the chemical energy as it breaks down the food

That was already in the bagel. Toasting does not add any.

Maillard reaction, isn't that chemical change, or is it just chemical change that is not producing chemical energy?

I think it does not add chemical energy.

 

[CAT 2]

So basically chemical energy does not belong. It should look like this:

3. Electric to radiant and thermal energy.

[QUOTE="haruspex, .Thermal energy can be listed because no conversion is 100% efficient. There is is always some friction, or resistance in electrical cables, etc., though whether the question expects you to worry about that I am not sure.[/QUOTE]

This isn't very advanced physics, will they take off points if I do have thermal energy listed? For other things they have told me not to worry about the extra energy, but they didn't mention anything here...
In their example they talked about wind turbines and said,'Energy transformations: kinetic energy of air to kinetic energy of turbine to electrical energy.' We discussed 4 types of producing electricity (wind, solar, biomass, and tidal) and what the energy transformations for those where. Only in biomass did thermal energy come up. What do you think about including or not including thermal energy in my answers?

 

[haruspex]

What do you think about including or not including thermal energy in my answers?

Sounds like you can safely omit it for 1 and 2, though obviously not for 3.
For 3, where do you think most of the heat energy ends up?
By the way, purists say heat only relates to the transfer of energy. When something is hot, we say it has internal energy.

 

[CAT 2]

Well, I don't know if you read this:

- elastic potential energy - kinetic energy - electrical energy
- chemical potential energy - sound energy - radiant energy
- nuclear potential energy - thermal energy - gravitational potential energy

But these are the only types I was supposed to work with.

Am I still missing one?

 

[CAT 2]

Does that mean heat energy is not something I should have in there?

 

[haruspex]

Does that mean heat energy is not something I should have in there?

Sorry, my post was a bit confusing.
As I wrote, heat only refers to transfer of energy. Once it has been transferred it takes the form of internal energy. Thermal energy is a special case of internal energy; it only relates to temperature changes. When ice at 0C melts to become water at 0C it has gained internal energy but not thermal energy.

If you were told to consider thermal energy, but not internal energy, that is a bit of a problem for the toasting bagel. But perhaps you have not been introduced to the concept of internal energy, so it is all being called thermal.
Anyway, can you answer my question, given that hint. Where did most of the energy end up?

 

[CAT 2]

Maybe in the air? Kinetic energy? I really don't know.

And yes I was not introduced to internal energy. Does that make a difference?

 

[haruspex]

Maybe in the air? Kinetic energy? I really don't know.

And yes I was not introduced to internal energy. Does that make a difference?

Which is heavier, a toasted bagel or an untoasted one? What has happened?

 

[CAT 2]

The toasted bagel is lighter. It has dried out. The water/ moisture has been removed. Are you saying an energy symbolizes this? Because I can't figure out which one.

 

[haruspex]

The toasted bagel is lighter. It has dried out. The water/ moisture has been removed. Are you saying an energy symbolizes this?

Yes. This is the latent heat of vaporisation, which is internal energy but not thermal energy.
When water is heated, the molecules move faster. This is thermal energy. But they still stay close to each other, held by the hydrogen bonds. As further heat is added, some of the molecules escape. The work done against those bonds in escaping is internal energy, but it isn't thermal energy because the molecular speed does not increase.

I suggest that in bagel toasting that is where most of the energy ends up.

 

[CAT 2]

But they didn't teach me about internal energy so I shouldn't put it in, right?

 

[haruspex]

But they didn't teach me about internal energy so I shouldn't put it in, right?

That's up to you. It's your judgment whether it will earn extra credit or just get you into an argument.

 

[CAT 2]

Alright, thanks for the help. I'll probably not put it in because this is an online course and they are pretty terrible about it. They don't argue they just mark wrong.

 

[LonelyElectron]

Alright, thanks for the help. I'll probably not put it in because this is an online course and they are pretty terrible about it. They don't argue they just mark wrong.

I also struggled with this one, but what you figured out makes a lot of sense! Have you submitted yet? Were your answers in fact marked correct by these aggravating teachers?

 

[CAT 2]

I haven't submitted it yet but I should know by the end of the week, have you?

 

[LonelyElectron]

Nope, still on lesson 15 . Best of luck then! Nice to meet a physics buddy in the same "class".