Basic Physics Question

[Trixxie]

MauiGal
Thanks for your question. I too never took Physics in High School, nor Algebra or Geometery. When I see the formulas for the physic's of the Dive Master all I see is a jungle, I don't even see a forest for the trees. :shakehead
I went to school to be an aircraft mechanic and ended up flying them instead. Algebra, Physic's in aviation? I add, subtract, multiply and divide and look at charts. This half life stuff I understand but controlling compartments? I just wish they would put a simple formula out with some examples so I can work them out. Verbiage with a math problem is WRONG for those like me. The workbook is great, I think. I also tried to learn Technical Analysis for stock picking and when I thought it said sell it was saying buy and vice versa.
Hang in there, even us mathmatically challenged will figure it out.

thanks Aggiedad! glad I am not the only mathmatically challenged diver out there..:cheering:
makes me wonder why my trivia team members want me to keep score and figure who owes what on the check for dinner... :eek_2:

 

[Trixxie]

Now think of a tub of cold water, and you run the faucet on hot. At first, the only warm part of the water is the part near the faucet. The other end of the tub is still cold. Over time, though, the water will move around, and the heat will be transported to the other end. This heat transport happened because the medium (the water) actually moved to take the heat to the other end.

this is convection, right? because heat is moving within a fluid?
so if it moves from one medium to another it's conduction?
:huh:

 

[Walter]

Convection is transfer of heat by movement of matter. Boiling water is an example. Conduction transfers heat from the heat source to the pot and from the pot to the water, but when the water heats, it physically moves bringing it's acquired heat with it. That movement of water is an example of convection.

Since matter does not move from our bodies out into the water, the heat transfer is not convection.

 

[paolov]

this is convection, right? because heat is moving within a fluid?

heat is transfered within a fluid... tneds to go to an equilibrium state.

so if it moves from one medium to another it's conduction?
:huh:

yes. transfered from one medium to another by proximity.



Imagine this :

from skin to wetsuit conduction plays in the heat trasfer

from wetsuit to the sea it is convection


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[Nomad]

Mauigal,

In your kitchen, you have an appliance called a "convection" oven. It cooks by heating the air, then the air flows around the food.

Conduction, as radinator already stated, is when the heat moves through a solid.

Don't overthink it.

 

[hdtran]

Ok maybe I am just a little dense. I never took Physics in H/S just Physiology. (went to college to be an auto mechanic but that is another story)

Just started my D/M classes and am doing the diving encyclopedia workbook. One of the first questions has to do with Convection and Conduction. asking which one affects a diver more in terms of heat loss.

Well if conduction is the movement of heat through direct contact and convection is the movement of heat through fluids (gas or actual fluid) then if a diver is in the water and is losing heat why is this conduction and not convection? OK I realize the water touching the skin is conduction but why is it not convection since fluids are involved.........

Convection is the combination of conduction together with movement (of something). You're in Atlanta. On a hot day, you feel really hot (let's leave sweating out of it for now. Actually, you're a gal, so you glow, you don't sweat ). If there's a breeze, you feel cooler, even if the air temperature is the same. That's because your body heat goes to the air, which is then blown away from you.

If you're in water, water can soak up heat (from your body) a gazillion times better than air. (That's why we can survive in 70F air for hours, clothed or not; but if you're thrown into a 70F swimming pool, you'll get hypothermia in a few hours). Furthermore, as the water flows past you (from swimming, twitching, etc.), you lose even more heat.

So, the exposure protection both cuts down the conduction of your body heat to the sea, and essentially eliminates convection of water next to your skin. You still get convection of water on the outside of your exposure suit, but that's relatively minor. I could do the math, but then, I'd have to charge you $219/hr consulting fee

The third way of transferring heat (besides conduction & convection) is radiation. Radiation does not require a medium to transfer the heat. Radiation tends to be minor when the difference in temperature is small (98F to 56F, for example). When the difference in temperature is large (say 1200F to 98F), radiation can be a major component in transferring heat.

We say that water has a much larger heat capacity than air, in other words, it takes a lot more energy to heat up some amount of water, as opposed to the same amount of air. That's another reason (besides the higher conductivity of water) why you feel cool when you stick your hand in room temperature water. Your body is taking more energy to warm the water to body temperature than it takes to warm air to body temperature. (The "amount of water" above can refer to equal volumes, equal masses, etc.)

 

[paolov]

talking about not to overthink .....





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[Walter]

from wetsuit to the sea it is convection

That's also conduction.

 

[Trixxie]

:lightbulb :lightbulb :lightbulb
Thanks everyone!

 

[paolov]

That's also conduction.

to clarify, i agree there is a confusing element to that

from wetsuit to sea it is conduction, however with movement of water current and of the diver moving underwater on the wetsuit, convection has more effect than conduction....


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