thermodynamics (I + II)

Question 1

what is metabolism?

Answer 1

the processes involved by the body in energy intake, storage, and use

• also the sum of the chemical processes performed by all cells to keep the body alive

Question 2

the body uses energy from food to

Answer 2

• operate organs
• maintain a constant temperature
• do external work
• build a stored energy supply (fat) for later uses

Question 3

what is thermodynamics?

Answer 3

the study and application of the thermal energy of systems

Question 4

what is heat (∆Q)?

Answer 4

the thermal energy that flows from one (hotter) body or system to another (colder) system in contact with it

Question 5

what does the zeroth law of thermodynamics state?

Answer 5

if bodies A and B are each in thermal equilibrium with a third body C, then A and B are in thermal equilibrium with each other

Question 6

in what other way can conservation of energy in the body be written?

Answer 6

changed in stored energy in the body = heat lost from the body + work done

Question 7

for a temperature change (∆T), a change (∆L) in any linear dimension (L) is given by

Answer 7

∆L = Lα∆T

Question 8

the change ∆V in the volume of a solid or liquid is given by

Answer 8

∆V = Vβ∆T

Question 9

what is specific heat capacity (c)?

Answer 9

the quantity of heat required to change the temperature of unit mass of a substance by one degree

Question 10

what is the average specific heat of the body?

Answer 10

0.83 kcal/kg˚C

Question 11

what is thermal conductivity (K)?

Answer 11

• it describes how temperature varies spatially due to the heat flow between different regions that are separated by a distance ∆x
• it also describes how much heat flows due to this spatial variation in temperature

Question 12

what does the efficiency of a heat engine describe?

Answer 12

how efficiently it turns heat into work

η = work done / energy consumed

Question 13

humans have an efficiency of

Answer 13

5.8%

Question 14

what is mechanical work?

Answer 14

the force you apply to an object multiplied by the distance you push or pull it

Question 15

what is latent heat of transformation (L)?

Answer 15

the amount of energy required per unit mass to change the state (but NOT the temperature) of a particular material

Question 16

equation of latent heat

Answer 16

Q = Lm

L - latent heat
m - mass

Question 17

what is the heat of vaporization (Lv)?

Answer 17

the amount of energy per unit mass that must be added to vaporize a liquid or removed to condense a gas

Question 18

what is the heat of fusion (Lf)?

Answer 18

the amount of energy per unit mass that must be added to melt a solid or removed to freeze a liquid

Question 19

what are the 4 modes of heat loss?

Answer 19

1. radiation loss (54-60% heat loss)
2. convection and conduction (=25% loss)
3. evaporation of sweat (=7% heat loss)
4. evaporation of water through breathing (=14% heat loss)

Question 20

the magnitude and importance of modes of heat loss depend on

Answer 20

clothing, environment, surroundings

Question 21

what is meant by radiation?

Answer 21

an object and its environment can exchange energy as heat via electromagnetic waves

ex: standing in front of a big fire and getting warmed by absorbing thermal radiation from the fire

Question 22

energy transferred through radiation is known as?

Answer 22

thermal radiation

Question 23

in planck’s law, a black body is essential. what is a black body?

Answer 23

1. a body that absorbs all the thermal radiation falling onto it
2. at thermal equilibrium, it emits as much energy as it absorbs
3. a good absorber of radiation and a good emitter of radiation

Question 24

radiation incident on an object can be

Answer 24

1. reflected by it
2. absorbed by it
3. transmitted through it

Question 25

what is emissivity?

Answer 25

the fraction of energy incident on the object that is absorbed

Question 26

what surfaces have the highest emissivity?

Answer 26

dull, black surfaces

Question 27

what does the Stefan-Boltzman Law state?

Answer 27

it gives the energy per second (power) radiated by the surface

P = e σ A T4

P - power radiated (watts)
e - emissivity (no units)
σ - stefan-boltzman constant
A - surface area (m^2)
T - temperature (K)

Question 28

what is the value of the Stefan-Boltzman constant?

Answer 28

5.67 x 10^-8

Question 29

the equation to calculate the difference between the energy radiated by the body and the energy absorbed from radiation from the surroundings

Answer 29

Hr = Kr Ar e (Ts - Tw)

Hr - rate of energy loss or gain due to radiation

Kr - parameter about 2.1 x 10^4

Ar - effective body surface area emitting the radiation

e - emissivity

Ts - skin temp (in ºC)
Tw - surrounding walls temp (in ºC)

Question 30

what is meant by conductivity?

Answer 30

it occurs when thermal energy moves through a material as a result of collisions between free electrons, ions, atoms, and molecules of the material

Question 31

what is the quantity ∆T/∆x?

Answer 31

• the temperature gradient
• the rate of change of temperature with distance (in a body)

Question 32

the temperature difference of two faces of a body is given by

Answer 32

∆ T = T1 - T2

T1 is one face, T2 is the other

Question 33

the quantity of heat ∆Q transmitted from face 1 to face 2 of the body in time T is given by

Answer 33

∆Q / ∆t = kT A ∆T / ∆x

kT - thermal conductivity (depends on the material of the body)

Question 34

what is the coefficient of conduction heat transfer (h)?

Answer 34

h = kT / ∆x

so we can rearrange the equation into ∆Q / ∆t = h A ∆T

Question 35

what is meant by convection?

Answer 35

• energy transfer that occurs when a fluid (ex: air) encounters an object (ex: match) whose temperature is higher than that of the fluid
• the temp of the part of the fluid in contact with the hot object increases, the fluid expands and becomes less
• because of this expanded fluid is now lighter than the surrounding cooler fluid, buoyant forces cause it to rise

Question 36

the heat lost due to convection (Hc) is given by

Answer 36

Hc = Kc Ac (Ts - Ta)

Kc - parameter with value 3.1

Ac - effective body surface area

Ts - skin temp
Ta - air temp

Question 37

what occurs during convection within the body?

Answer 37

it does not change the average body temperature, but the distribution of temperature within the body

Question 38

when is heat production high?

Answer 38

at low temperatures

Question 39

heat production decreases with increasing temperature until _____ becomes constant, and increases again with _____

Answer 39

Tc (lower critical temperature)
Th (upper critical temperature)

Question 40

1. between Tc and Th is?
2. below Tc is?
3. above Th is?

Answer 40

1. thermoneutral zone (the zone of minimal metabolism)
2. the heat loss increases due to radiation and convection
3. the heat loss is dominated by evaporation

Question 41

what is hypothermia?

Answer 41

when body temperature cannot be regulated and there is body cooling

Question 42

when does vasoconstriction occur?

Answer 42

when the internal body temp gets too low, the blood vessels constrict to reduce the rate of heat loss

Question 43

what is piloerection?

Answer 43

• when the fine body hairs stand on end in an attempt to reduce convective heat loss from the skin
• the raising of hairs is intended to create a stationary layer of air between the skin & surroundings

Question 44

when does perspiration/sweat occur?

Answer 44

when the latent heat of evaporation of water is high