Question

What is the primary mode of energy transfer away from your body
a) on a very windy day?
b) on a cold day with no wind?
1/conduction
2/convection
3/radiation
Please

Answer 1

@ybarrap

Answer 2

it seems like convection is it not?
the heat leaves the source and since heat is less dense, it rises

Answer 3

a- convection, heat is carried away from skin via air currents
b-conduction because heat is carried away via a temperature gradient

Answer 4

I confused. Why?
the heat goes from our body , in other word, our body is a "stove" , why is it not radiation?

Answer 5

If so, what is kind of energy transfer from a hair dryer to your wet hair?

Answer 6

i think that's convection...

Answer 7

I think of radiation as electromagnetic waves - like radiation from the sun -- that's not conduction -- there are no particles between the sun and the earth to transfer heat

conduction as transfer of heat via particle collisions

Hair dryer is using some convection but also conduction by causing temperature gradient on hair

Answer 8

@ybarrap isn't it because the most predominant radiation through electromagnetic waves? one example i can think of off the top of my head is blackbody radiation

Answer 9

Radiation goes as the difference in the fourth powers of the absolute temperatures of the body and its environment, not likely large for humans and ambient air.

Answer 10

Stefan's Law
\[P=\sigma AeT^4\]

Answer 11

I think the last one is convection,

Answer 12

No- For example, convection is one means of cooling via AC systems. The other two being reduction in humidity and reduction in temperature. Here some info on convection via wind http://en.wikipedia.org/wiki/Convection#Heat_transfer

Answer 13

Law of thermal conduction
\[P=kA|{dT\over dx}|\]

since on a cold day, there is a temperature difference, it is thermal conduction because there is a temperature difference

Answer 14

2/ A 0.5 kg block of aluminium (c_a= 900J/kg C) is heated to 200degree C. The block is then quicly placed in an insulated tub of cold water at 0 degree C (c_w= 4186J/kg C) and sealed.
At equilibrium, the temperature of the water and block are measured to be 20degree C
If replace 100g of the 0degree C water by 100g of 0degree C ice, what is the final temperature?
I don't think there is any change. so, the final temperature is 20, am I right?

Answer 15

"What is the primary mode of energy transfer away from your body"
a) on a very windy day? ---------- Convection
b) on a cold day with no wind? ---- Radiation

In layman's language:
Conduction - energy is transferred without net displacement of particles of the medium
Convection - energy is transferred due to displacement of particles of the medium
Radiation - energy transfer doesn't require any material medium

Answer 16

"...If replace 100g of the 0degree C water by 100g of 0degree C ice, what is the final temperature?..."

The final temperature would be less than 20 ℃ (guess why? ;)

Answer 17

@LastDayWork I don't think so:)
The equation to calculate equilibrium of the set is \(Q_1 +Q_2=0\)
where Q = mc (\(T_{final} - T_{initial}\)) and they calculate it is \(20^0 C\)
In the equation, there is no term relate to the phase of the material but temperature. If you said that the temperature will decrease, please, tell me why.

Answer 18

Think about the latent heat..

Answer 19

Do you indicate to inertial energy of ice > it is of water?

Answer 20

Actually, I was trying to say that the internal energy of ice is less than that of water (when both are at 0 ℃

Answer 21

I can write the equation for the drop in temperature to prove my point..but I think it would be better if you learn to use the physical interpretations.

Answer 22

Thanks for suggestion. I will find it out. I have a lot of problem in understanding physics terminology. :)

Answer 23

Read this book, if you could spare some time..my personal favorite :)
http://www.feynmanlectures.caltech.edu/

Answer 24

Thank you.

Answer 25

The liquid phase has a higher internal energy than the solid phase. This might help - http://en.wikipedia.org/wiki/Latent_heat_of_fusion

Answer 26

100g of water = ?? g of ice?