11. THERMODYNAMICS Flashcards
1
Q
- What do all activities of the human body involve?
A
- energy consumption
2
Q
- What is metabolism?
A
- the processes of the body that involve:
- energy intake
- storage
- use of energy - it is any energy usage by the body
- it is also the sum of all the chemical processes performed by the cells
- they do this is in order to keep the body alive
3
Q
- What is the body, from a physics perspective?
A
- it is an energy converter
- this means that it is subject to the law of conservation of energy
4
Q
- What 4 functions does the body do with the energy that it takes in from food?
A
- it operates its organs
- it maintains a constant temperature
- it does external work
- it builds a stored energy supply (fat) for later needs
5
Q
- What is thermodynamics?
A
- it is the study and application of the thermal energy of systems
6
Q
- What is a central topic of Thermodynamics?
A
- temperature
7
Q
- What is temperature?
A
- it is a measure of how hot or cold something is
- it is how we measure heat
- it is one of the seven SI base quantities
8
Q
- What is temperature usually measured in?
A
- Celsius
- Fahrenheit
- Kelvin Scale
9
Q
- What is the SI unit for temperature?
A
- Kelvins (K)
10
Q
- What limits does the temperature of the body have?
A
- it has no upper limits
- it has a lower limit
11
Q
- What is the lower limit of body temperature?
A
- the limiting low temperature is taken as the zero of the Kelvin Temperature scale
- this is equal to -273.15 °C
- this is equal to -459.67 °F
12
Q
- What equation do we use to move from Celsius to Fahrenheit?
A
T (F°) = T (C°) x 9/5 + 32
13
Q
- What equation do we use to move from Kelvin to Celsius?
A
T (C°) = T (K) - 273.15
14
Q
- What is Heat (▵Q)?
A
- it is the thermal energy that flows from one body or system to another
- the two systems are in contact with each other
- it flows from one system to another due to their temperature differences
15
Q
- How does heat always flow?
A
- from hot to cold
- the movement of thermal energy is always from hot to cold
16
Q
- What is the SI unit for Heat?
A
- Joules (J)
17
Q
- What are two other units for heat?
A
- calories
(1 cal= 4.184 J) - British thermal unit
(1 Btu= 1054 J)
18
Q
- What does it mean when two systems are in equilibrium?
A
- they are balanced
- they share a property (temperature)
19
Q
- What is thermal equilibrium?
A
- it is when two systems are in thermal contact:
- they exchange energy until an equilibrium state is
reached - then no more net energy transfer occurs
- they exchange energy until an equilibrium state is
20
Q
- What does the zeroth law of thermodynamics state?
A
- If Bodies A and B are in thermal equilibrium with a third body C
- then body A and B are in thermal equilibrium with each other
21
Q
- What is the message of the zeroth law?
A
- every body has a property called temperature
- when two bodies are in thermal equilibrium:
- their temperatures are equal and vice versa
22
Q
- How can the conservation of the energy in the body be written?
A
Change in the stored energy in the body
=
Heat lost from the body + the work done
23
Q
- What do we use the first law of thermodynamics to investigate?
A
- the continuous energy changes in the body
24
Q
- What is the First Law of Thermodynamics?
A
- The First Law of Thermodynamics states that energy cannot be created or destroyed; it can only be converted from one form to another.
25
Q
- What is the equation for the first law of Thermodynamics?
A
▵U = Q - W
▵U= the change in the internal energy
Q= the heat added to the system
W= the work done by the system
26
Q
- What change does an object experience when it changes its temperature?
A
- it changes size
- there is a change in any linear dimension (▵L)
when there is a change in temperature (▵T)
27
Q
- What is the equation we use to find the change in any linear dimension/ size of the object?
A
▵L = L . ⍺ . ▵T
⍺= the coefficient of linear expansion
28
Q
- What is the equation we use to find out the change in volume (▵V) in a solid or a liquid?
A
▵V = V . β . ▵T
β= the coefficient of volume expansion
= 3⍺
29
Q
- What is the specific heat capacity (c)?
A
- it is the quantity of heat that is required to change the temperature of unit mass
of a substance
by one degree
30
Q
- What equation will we use to work out the specific heat capacity?
A
c = ▵Q / m . ▵T
c= specific heat capacity
▵Q= quantity of heat
m = mass
▵T= temperature change
31
Q
- What is the SI unit of the specific heat capacity (c)?
A
- J/kg.K
- other units also include:
- kcal
- kg. °C
32
Q
- What does each substance have?
A
- it has a characteristic value of specific heat
- this varies slightly with temperature
33
Q
- What is the characteristic value of specific heat for water?
A
- c water = 1 kcal/kg.°C
= 4180 K/kg.°C - this value changes dependent on the phase water is found in
(liquid, solid, vapour)
34
Q
- What is the average specific heat for the human body
A
- c body = 0.83 kcal/kg.°C
- this means that it takes 83kcal to raise the temperature of a 100kg person by 1°C
35
Q
- What does Thermal Conductivity (K) describe?
A
- it describes how temperature varies spatially
- this is due to the heat flow between different regions
- these regions are separated by a distance (▵x)
- it also describes how much heat flows due to the spatial variation in temperature
36
Q
- How would we mathematically write the relation between heat flow and spatial variation in temperature?
A
1 dQ ▵T
—– x ——– ≈ -K ————
A dt ▵x
- this is known as heat flux
- the minus sign indicates that the heat flows from hotter regions to colder regions
37
Q
- What is a consequence of thermal dynamics?
A
- heat engines that convert chemical energy to heat
- and that use heat for mechanical work
- have a limited efficiency to do such useful mechanical work
38
Q
- What does the efficiency of a heat engine describe?
A
- how efficiently it turns heat to work
- how well-organised it is
- how much max productivity it can do with minimum waste
39
Q
- How do we work out the efficiency ?
A
Work Done
n = —————————-
Energy Consumed
40
Q
- What is the % of human efficiency?
A
- 5.8%
41
Q
- What value does efficiency rarely exceed?
A
- 20%
42
Q
- What does the first law of thermodynamics show?
A
- it shows that stored energy can be used to supply heat or work
- this is known as mechanical work with regards to people
43
Q
- What is the mechanical work?
A
the force you apply to an object
x
the distance you push or pull it by
44
Q
- Read through this summary.
Does everything make sense
A
- yes
45
Q
- Read through this summary.
Does everything make sense
A
- yes
46
Q
- Read through this summary.
Does everything make sense
A
- yes
47
Q
- Read through this summary.
Does everything make sense
A
- yes
48
Q
- Read through this summary.
Does everything make sense
A
- yes
49
Q
- Read through this summary.
Does everything make sense
A
- yes
