11. THERMODYNAMICS

Question 1

1. What do all activities of the human body involve?

Answer 1

• energy consumption

Question 2

2. What is metabolism?

Answer 2

• 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

Question 3

3. What is the body, from a physics perspective?

Answer 3

• it is an energy converter
• this means that it is subject to the law of conservation of energy

Question 4

4. What 4 functions does the body do with the energy that it takes in from food?

Answer 4

• it operates its organs
• it maintains a constant temperature
• it does external work
• it builds a stored energy supply (fat) for later needs

Question 5

5. What is thermodynamics?

Answer 5

• it is the study and application of the thermal energy of systems

Question 6

6. What is a central topic of Thermodynamics?

Answer 6

• temperature

Question 7

7. What is temperature?

Answer 7

• 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

Question 8

8. What is temperature usually measured in?

Answer 8

• Celsius
• Fahrenheit
• Kelvin Scale

Question 9

9. What is the SI unit for temperature?

Answer 9

• Kelvins (K)

Question 10

10. What limits does the temperature of the body have?

Answer 10

• it has no upper limits
• it has a lower limit

Question 11

11. What is the lower limit of body temperature?

Answer 11

• 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

Question 12

12. What equation do we use to move from Celsius to Fahrenheit?

Answer 12

T (F°) = T (C°) x 9/5 + 32

Question 13

13. What equation do we use to move from Kelvin to Celsius?

Answer 13

T (C°) = T (K) - 273.15

Question 14

14. What is Heat (▵Q)?

Answer 14

• 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

Question 15

15. How does heat always flow?

Answer 15

• from hot to cold
• the movement of thermal energy is always from hot to cold

Question 16

16. What is the SI unit for Heat?

Answer 16

• Joules (J)

Question 17

17. What are two other units for heat?

Answer 17

• calories
  (1 cal= 4.184 J)
• British thermal unit
  (1 Btu= 1054 J)

Question 18

18. What does it mean when two systems are in equilibrium?

Answer 18

• they are balanced
• they share a property (temperature)

Question 19

19. What is thermal equilibrium?

Answer 19

• 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

Question 20

20. What does the zeroth law of thermodynamics state?

Answer 20

• 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

Question 21

21. What is the message of the zeroth law?

Answer 21

• every body has a property called temperature
• when two bodies are in thermal equilibrium:
  - their temperatures are equal and vice versa

Question 22

22. How can the conservation of the energy in the body be written?

Answer 22

Change in the stored energy in the body
=
Heat lost from the body + the work done

Question 23

23. What do we use the first law of thermodynamics to investigate?

Answer 23

• the continuous energy changes in the body

Question 24

24. What is the First Law of Thermodynamics?

Answer 24

• The First Law of Thermodynamics states that energy cannot be created or destroyed; it can only be converted from one form to another.

Question 25

25. What is the equation for the first law of Thermodynamics?

Answer 25

▵U = Q - W ▵U= the change in the internal energy Q= the heat added to the system W= the work done by the system

Question 26

26. What change does an object experience when it changes its temperature?

Answer 26

- it changes size - there is a change in any linear dimension (▵L) when there is a change in temperature (▵T)

Question 27

27. What is the equation we use to find the change in any linear dimension/ size of the object?

Answer 27

▵L = L . ⍺ . ▵T ⍺= the coefficient of linear expansion

Question 28

28. What is the equation we use to find out the change in volume (▵V) in a solid or a liquid?

Answer 28

▵V = V . β . ▵T β= the coefficient of volume expansion = 3⍺

Question 29

29. What is the specific heat capacity (c)?

Answer 29

- it is the quantity of heat that is required to change the temperature of unit mass of a substance by one degree

Question 30

30. What equation will we use to work out the specific heat capacity?

Answer 30

c = ▵Q / m . ▵T c= specific heat capacity ▵Q= quantity of heat m = mass ▵T= temperature change

Question 31

31. What is the SI unit of the specific heat capacity (c)?

Answer 31

- J/kg.K - other units also include: - kcal - kg. °C

Question 32

32. What does each substance have?

Answer 32

- it has a characteristic value of specific heat - this varies slightly with temperature

Question 33

33. What is the characteristic value of specific heat for water?

Answer 33

- c water = 1 kcal/kg.°C = 4180 K/kg.°C - this value changes dependent on the phase water is found in (liquid, solid, vapour)

Question 34

34. What is the average specific heat for the human body

Answer 34

- c body = 0.83 kcal/kg.°C - this means that it takes 83kcal to raise the temperature of a 100kg person by 1°C

Question 35

35. What does Thermal Conductivity (K) describe?

Answer 35

- 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

Question 36

36. How would we mathematically write the relation between heat flow and spatial variation in temperature?

Answer 36

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

Question 37

37. What is a consequence of thermal dynamics?

Answer 37

- 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

Question 38

38. What does the efficiency of a heat engine describe?

Answer 38

- how efficiently it turns heat to work - how well-organised it is - how much max productivity it can do with minimum waste

Question 39

39. How do we work out the efficiency ?

Answer 39

Work Done n = ---------------------------- Energy Consumed

Question 40

40. What is the % of human efficiency?

Answer 40

- 5.8%

Question 41

41. What value does efficiency rarely exceed?

Answer 41

- 20%

Question 42

42. What does the first law of thermodynamics show?

Answer 42

- it shows that stored energy can be used to supply heat or work - this is known as mechanical work with regards to people

Question 43

43. What is the mechanical work?

Answer 43

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

Question 44

44. Read through this summary. Does everything make sense

Answer 44

- yes

Question 45

45. Read through this summary. Does everything make sense

Answer 45

- yes

Question 46

46. Read through this summary. Does everything make sense

Answer 46

- yes

Question 47

47. Read through this summary. Does everything make sense

Answer 47

- yes

Question 48

48. Read through this summary. Does everything make sense

Answer 48

- yes

Question 49

48. Read through this summary. Does everything make sense

Answer 49

- yes