90
2.9.2 Second Law of Thermodynamics
The second law of thermodynamics states that the total entropy (a measure of the
unavailable energy in a closed system) of a system either increases or remains constant; it never decreases.
With respect to human body, the energy generated by human body by metabolism is transferred to the environment by radiation, convection, and conduction.
If an amount of heath Q flows into human body at constant temperature T, then
its entropy S increases by ΔS = Q/T.
If two heat reservoirs, the environment (R 1 ) and the human body (R 2 ), are at temperatures T 1 and T 2 , and if an amount of heat Q flows from R 1 to R 2 , then the net
entropy change for these two reservoirs is:
∆S Q T
Q T
= (
)− (
)
/
/
2
1
ΔS is positive, provided that T 1 > T 2 .
As per the second law of thermodynamics, total entropy of a system either
increases or remains constant; it never decreases.
Since the temperature of the environment varies, temperature within the human
body is maintained by increasing (by shivering, increase in blood transport) or
decreasing (by sweating) it in natural settings.
When the body fails to comply with the second law of thermodynamics in natural
settings, the person has to:
• Change the temperature of the immediate surroundings (e.g., by air conditioner/
cooler or room heater as per the situation).
• Wear warm cloths to conserve energy if the person is feeling cold.
• Perform physical activity to increase catabolic activity to release energy within
the body.
• Consume food/drinks with warm/cold temperature (as per the situation).
Failure to comply with the second law of thermodynamics by a healthy person
will disturb his health.
2.9.3 Third Law of Thermodynamics
The third law of thermodynamics states that the entropy of a perfectly ordered solid
at absolute zero (0° K) is zero.
Thermal energy is transferred from one point to another by radiation, convection,
and conduction. In conduction, heat is transferred by direct transfer of heat through
the matter, due to the variation in temperature, among adjacent parts of the object.
In convection, heat is transferred by movement of matter in fluids. In radiation, the
heat transferred is by radiation.
2 Fundamentals of Physics for Environmental and Medical Professionals
2.9.2 Second Law of Thermodynamics
The second law of thermodynamics states that the total entropy (a measure of the
unavailable energy in a closed system) of a system either increases or remains constant; it never decreases.
With respect to human body, the energy generated by human body by metabolism is transferred to the environment by radiation, convection, and conduction.
If an amount of heath Q flows into human body at constant temperature T, then
its entropy S increases by ΔS = Q/T.
If two heat reservoirs, the environment (R 1 ) and the human body (R 2 ), are at temperatures T 1 and T 2 , and if an amount of heat Q flows from R 1 to R 2 , then the net
entropy change for these two reservoirs is:
∆S Q T
Q T
= (
)− (
)
/
/
2
1
ΔS is positive, provided that T 1 > T 2 .
As per the second law of thermodynamics, total entropy of a system either
increases or remains constant; it never decreases.
Since the temperature of the environment varies, temperature within the human
body is maintained by increasing (by shivering, increase in blood transport) or
decreasing (by sweating) it in natural settings.
When the body fails to comply with the second law of thermodynamics in natural
settings, the person has to:
• Change the temperature of the immediate surroundings (e.g., by air conditioner/
cooler or room heater as per the situation).
• Wear warm cloths to conserve energy if the person is feeling cold.
• Perform physical activity to increase catabolic activity to release energy within
the body.
• Consume food/drinks with warm/cold temperature (as per the situation).
Failure to comply with the second law of thermodynamics by a healthy person
will disturb his health.
2.9.3 Third Law of Thermodynamics
The third law of thermodynamics states that the entropy of a perfectly ordered solid
at absolute zero (0° K) is zero.
Thermal energy is transferred from one point to another by radiation, convection,
and conduction. In conduction, heat is transferred by direct transfer of heat through
the matter, due to the variation in temperature, among adjacent parts of the object.
In convection, heat is transferred by movement of matter in fluids. In radiation, the
heat transferred is by radiation.
2 Fundamentals of Physics for Environmental and Medical Professionals