week 4

Question 1

Frequency (f) -

Answer 1

number of repetitions of a complete oscillation per unit time. Measured in cycles per second, or hertz (Hz).

Question 2

Period (T) -

Answer 2

time interval between the successive occurrences of a particular phase of an oscillation

Question 3

Simple harmonic motion, SHM -

Answer 3

type of periodic motion in which the restoring force is proportional to the displacement from the equilibrium position

Question 4

Hooke’s Law:

Answer 4

Within the elastic limits of a material, the strain is proportional to the stress, i.e., the amount of deformation is proportional to the distorting force.

Question 5

mechanical properties of different body components begins by

Answer 5

investigating their stress-strain relationships

Question 6

What we model in stress-strain relationship and what the models are used for?

Answer 6

We model:
• body components’ nonlinear time-dependent properties and
• their time-dependent, viscoelastic properties.

These models are used to:
• understand how bones can bend and
• the occurrence of fractures.

Question 7

simplest type of passive response -

Answer 7

harmonic or Hookean behavior

Question 8

Body components can be passive or active:

Answer 8

• Passive components (bones & tendons): respond to outside forces.
• Active elements (muscles), generate forces.

But this division is NOT IDEAL. Muscles are active elements and passive components depending on the situation.

Question 9

deformation depends

Answer 9

nonlinearly on force or stress

Question 10

plastic deformation -

Answer 10

for large stresses - irreversible => material never returns to the same size or shape when the stress is removed

Question 11

Extensive properties change when?

Answer 11

when the size of the object changes

Question 12

Elasticity -

Answer 12

property by which a body returns to its original size and shape when the forces that deform it are removed

Question 13

Strain (ε) -

Answer 13

fractional deformation resulting from a stress

Question 14

elastic limit -

Answer 14

point up to which the object returns to its initial length when the stress is removed (no permanent deformation)

Question 15

FOR STRESSES BEYOND THE ELASTIC LIMIT

Answer 15

THERE IS PERMANENT OR PLASTIC DEFORMATION

Question 16

where is yield point and its significance

Answer 16

at a stress higher than the elastic limit, above it much elongation can occur without much increase in the load.

Question 17

For tension, the material remains intact for larger stresses until

Answer 17

the ultimate tensile stress (UTS)

Question 18

Fracture is where?

Answer 18

if application of larger stress continues, fracture at point F, at a strain called the ultimate strain or the ultimate percent elongation (UPE)

Question 19

is ultimate compressive stress (UCS) different from ultimate tensile stress (UTS)?

Answer 19

yes

Question 20

for ligaments and tendons, there is resistance to

Answer 20

resistance to tension, but not to compression

Question 21

energy needed to break long bones -

Answer 21

fraction of that available from the kinetic energy in common collisions

Question 22

why do our bones not regularly break? (2)

Answer 22

because most of the energy is absorbed by:

• muscle contractions and
• the deformation of soft tissues

Question 23

Why bones fracture more easily in elderly ppl?

Answer 23

• their bones are weaker
• their tissues are less suited to absorb energy
• they may fall more awkwardly and with less body breaking action

Question 24

Bone fractures are determined by: (2)

Answer 24

• the mode of the applied loads and
• their orientations

Question 25

Bones in regards to various stimuli:

Answer 25

They are: • strongest in compression, • less strong in tension, and • weakest in shear.

Question 26

Bones usually break:

Answer 26

by shear stresses or under tension, but NOT UNDER COMPRESSION

Question 27

Fracture can be due to direct blows which break the bone:

Answer 27

• in two (non comminuted) at low energy (transverse fracture), or • into many pieces (comminuted) at high energy.

Question 28

Indirect blows, as in skiing, can lead to fractures that are:

Answer 28

• spiral, • oblique, • transverse with a butterfly fragment and so on.

Question 29

occurrence of fractures depends on

Answer 29

ultimate strength, defects, and specifically how loads are applied

Question 30

Kinds of fracture in terms of time:

Answer 30

- Bones can fracture when the stress on them **suddenly** exceeds a given failure limit - Bones can also fracture **more gradually** (due to damage from: *prolonged continuous stress* (sitting) or *prolonged cyclic stress* (fatigue due to walking or running).) - **Stress fracture**: rate of damage exceeds the rate of repair by the body and the bone fails

Question 31

metabolism -

Answer 31

processes involved by the body in energy intake, storage; More generally, metabolism is any energy usage by the body.

Question 32

thermodynamics -

Answer 32

study and application of the thermal energy of systems

Question 33

Heat (ΔQ)

Answer 33

thermal energy that flows from one body or system to another (in contact with it), due to their temperature difference

Question 34

direction of heat flowing -

Answer 34

HEAT ALWAYS FLOWS FROM HOT TO COLD

Question 35

zeroth law of thermodynamics:

Answer 35

“If bodies A and B are each in thermal equilibrium with a third body T, then A and B are in thermal equilibrium with each other.”

Question 36

The First Law of Thermodynamics -

Answer 36

- statement of the law of conservation of energy “If an amount of heat Q flows into a system => this energy must appear as increased internal energy ΔU for the system and/or work W done by the system on its surroundings.”

Question 37

specific heat capacity c -

Answer 37

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

Question 38

Thermal conductivity K describes

Answer 38

how temperature varies spatially due to the heat flow between different regions that are separated by a distance Δx. Ιt also describes how much heat flows due to this spatial variation in temperature.

Question 39

efficiency of a heat engine describes

Answer 39

how efficiently it turns heat into work humans ~5.8% usually much less than 20%, rarely exceeds this number

Question 40

four modes of heat loss:

Answer 40

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

Question 41

magnitude and importance of heat loss modes depend on (3):

Answer 41

clothing environment surroundings

Question 42

thermal radiation:

Answer 42

Energy transferred as heat is via electromagnetic waves

Question 43

black body is:

Answer 43

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 44

ε, emissivity:

Answer 44

fraction of energy incident on the object that is absorbed

Question 45

All objects whose temperature is above absolute zero, (do what?)

Answer 45

radiate energy

Question 46

Conduction:

Answer 46

Thermal energy moves through a material as a result of collisions between free electrons, ions, atoms and molecules of the material. When a temperature difference exists between materials in contact, the higher energy atoms in the warmer substance transfer energy to the lower energy atoms in the cooler substance. Heat flows from hot to cold.

Question 47

ΔΤ/Δx -

Answer 47

***temperature gradient*** - rate of change of temperature with distance

Question 48

k_T, thermal conductivity

Answer 48

depends on the material of the body

Question 49

thermal energy being transported upward by convection when?

Answer 49

Such energy transfer occurs when a fluid (air), comes in contact with an object (match) whose temperature is higher than that of the fluid: **temperature of the part of the fluid** that is in contact with the hot object **INCREASES** => that fluid **expands** and **becomes less dense** => expanded fluid is now **lighter** than the surrounding cooler fluid, buoyant forces cause it to **rise**

Question 50

h_c, convective heat transfer coefficient per unit area

Answer 50

decreases with heavier clothing and increases with less and lighter clothing: When you are nude you get cold faster because of increases in the above coefficient.

Question 51

convection within the body (flow of blood) in regards to average T of the body:

Answer 51

IT DOES NOT CHANGE THE AVERAGE TEMPERATURE OF THE BODY, BUT THE DISTRIBUTION OF TEMPERATURE WITHIN THE BODY

Question 52

T_c and T_h

Answer 52

T_c - lower critical T T_h - upper critical T Heat production is high at low temperatures, then decreases with increasing temperature until T_c, becomes constant, and then at T_h it increases again.

Question 53

Below T_c, the heat loss increases due to

Answer 53

radiation and convection

Question 54

Above T_h the heat loss is dominated by

Answer 54

evaporation

Question 55

Thermoregulation -

Answer 55

maintenance of a constant core body temperature in an organism

Question 56

physiological responses to T:

Answer 56

- **vasoconstriction** (narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles) ***to cold T*** - **vasodilation** (the widening of blood vessels) ***to hot T*** - **piloerection** - fine body hairs stand on end in an attempt to reduce convective heat loss from the skin (***to cold T***) - **shivering** ***to cold T***