Thermodynamics - Lecture 6

First Law of Thermodynamics-Energy ConservationQ is positive when heat transferred INW POSITIVE when work done by system on SOMETHING ELSE

First Law for Body-For the body along with the first law of thermodynamics, we also need to include the ENERGY INPUT, due to the metabolism of FOODFood Energy, E-Calorific Value in Cal, or KiloCal BUT we use JOULES OR KILOJOULES j or kJ-1 cal = 4.19kJ-measured by the heat produced with food oxidised (by combustion) then adjusted for how we metabolise food-recommended intake 8MJ females, 10MJ males

Work EfficiencyW- mechanical work done by body(E - change in U) - NET metabolic energy required to carryout work -If body does not add/use stored energy then (change in u) = 0 . Thus n= W/E ( then Q= -E)If (change in U) is NEGATIVE = WEIGHT LOSS -In body usually quite low ( 2-10%), 20-25%during exercise-When n -heat loss rate is usually about same at metabolic

Body ThermoregulationTemp sensitive receptors are-hypothalmus; w & c, integrates info from both skin and central receptors, provides signals (control rate heat loss/heat production)-skin - w & cold-abdominal visera (only warmth)These DICTATE thermal CONTROL options-perspiration-vasoconstriction-vasodilation-shiveringPerspiration -max moisture loss 2000w/p hour-if RH low, skin dry. Even when lots of sweat-RH increases MORE NOTES ON THESE