SYS 3023 > Exam 2 > Flashcards

Exam 2 Flashcards

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1
Q

What is Fitt’s Law?

A

The relationship between movement time (MT) and Index of Difficulty (ID)

as ID increases, MT linearly increases

MT = a + b * log_2(2D/W)
Where MT = Movement Time
a, b = empirically derived constants
D = distance of movement from start to target center
W = width of the target

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2
Q

What is movement time?

A

Movement time is the time required to physically make the response called the stimulus

Time required to complete a movement depends on the nature of the movement and the degree accuracy required

MT = a + b * log_2(2D/W)

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3
Q

What is the relative difficult of the task called for Fitt’s Law?

A

Index of Difficulty

ID = log_2(2D/W)

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4
Q

What is Hick’s Law?

A

The time required to make a decision (reaction time) is linearly related to the amount of information that must be processed in coming to that decision

Reaction Time = a + b * log_2(N)
Where N = number of choices
H = log_2(N); measured in bits

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5
Q

What does number of bits measure in Hick’s Law?

A

the number of choices (its information)

It is directly proportional to the number of bits of information, i.e., log_2(1/pi), where pi is the probability of each stimulus

Reaction Time = a * sum(pi * log_2(N)), but when stimuli are equally likely it turns into
Reaction Time = a + b * log_2(N)

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6
Q

What is anatomy?

A

study of the structure of the body

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7
Q

What is physiology?

A

study the functions and relationships of body parts

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8
Q

What is biomechanics?

A

study of the structure and function of biology systems by means of the methods of “mechanics”

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9
Q

What are reasons why we care about the musculoskeletal system?

A

we need to know physiological limits to properly design

Provide guidelines for design

Minimize costs of injuries

Older population

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10
Q

What are the 3 components of the musculoskeletal system?

A

Connective Tissues
Joints
Skeletal Muscles

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11
Q

Where are connective tissues found?

A

Bones, ligaments, tendons, cartilage

Mechanical system

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12
Q

Where are joints found?

A

Unions with DoF

Mechanical system

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13
Q

Where are skeletal muscles found?

A

Muscle fibers, connective tissues, nerve excitation

Force generations

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14
Q

What are the functions of connective tissues?

A

Force transmission and movement

Metabolism - Blood cell manufacture

Defense - Skin, vital organs

Storage / Buffer - Calcium and phosphorus

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15
Q

What are the two fiber types associated with connective tissues?

A

Collagen
Elastin

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16
Q

What are collagen fibers?

A

Collagen fibers make connective tissue strong and stiff, allowing it to withstand high tensile forces without stretching much.

They contribute to rigidity, structural integrity, and load-bearing capacity.

Tissues rich in collagen (e.g., tendons, ligaments) can handle high tension but have low elasticity.

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17
Q

What are elastin fibers?

A

Elastin fibers allow connective tissues to stretch and then return to their original shape.

They contribute to flexibility and resilience under deformation.

Tissues rich in elastin (e.g., skin, lung tissue, elastic arteries) can stretch repeatedly without losing shape.

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18
Q

What are mechanical properties of connective tissue determined by?

A

proportions of these fiber types and their geometric organization

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19
Q

What are tendons?

A

Connect muscle to bones

Mainly longitudinal collagen with some elastic fibers

E.g., multiple tendons with carpal tunnel

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20
Q

What are ligaments?

A

Connect bone to bone

Mainly longitudinal collagen with some oblique fibers and some elastin fibers

E.g., ACL injury

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21
Q

Mechanical properties of material

A

Correspond to the change in shape of material (strain) for different applied loads (stress)

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22
Q

What do mechanical properties depend on?

A

the physical structure or arrangement of the material being loaded

characteristics of force acting on the materials include:
- magnitude
- direction
- velocity, acceleration

temperature of material

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23
Q

What is stress?

A

force/unit area that results from an applied load (tension)

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24
Q

What is strain?

A

physical deformation response of a material
ex: elongation of material

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25
Describe collagen fibers stress-strain curve
large elastic modulus transmission of force residual strain; plastic deformation
26
Describe elastic fibers stress-strain curve
large strain with abrupt failure storage and release of energy
27
Some level of imposed stress/strain can lead to
adaptive changes tissue damage
28
What is Wolff's Law?
bone is deposited where needed and reabsorbed where not needed, based on the mechanical stresses on it
29
What body part does Wolff's Law relate to?
Joints
30
How does age affect bone density?
Older bones are less dense, weaker, and brittle
31
What are the functions of joints?
Interface between two bones Hold bones together, giving stability, but also gives skeleton mobility
32
What are the 3 types of joints?
Synovial Cartilaginous Fibrous
33
What are synovial joints?
Most common type No tissue; synovial fluid forms interface
34
Where are synovial joints located?
wrist, elbow, knee, shoulder
35
Label the structure of the synovial joint
Components: articular cartilage, joint capsule, synovial fluid, synovial membrane
36
Understand graph of relationship between number of bits and response time
Its a curved relationship where Response time increases as number of bits increases
37
What are bones?
Bones = levers moved by muscles they are attached
38
What are cartilaginous joints?
some motion, but high load bearing
39
Where are cartilaginous joints located?
spine, ribs-sternum
40
Where are fibrous joints located?
skull
40
What are fibrous joints?
immobile, fibrous tissues bridge joints
41
What are the 3 types of cartilage?
Hyaline Cartilage Fibrocartilage Elastic Cartilage
42
Where are hyaline cartilage?
on bones synovial joints, articular surfaces
43
Where are fibrocartilage?
on disc cartilaginous joints; intervertebral discs
44
Where are elastic cartilage?
ear and nose (form) anterior rib cage (motion)
45
Why is it difficult to recover from cartilage injuries?
initial/minor injuries may not be noticed, no nerves, no blood supply (diffusion)
46
What are the 2 variables that affect spine compressive strength?
age and gender (males > females)
47
What are the 6 factors that increase the risk of joint injury?
Aging Inflammation Gender Previous Injuries Loss of Muscle Mass Excess Weight
48
What happens to cartilage as we age?
cartilage thins as we age, so we lose its protection against grinding
49
What are the 4 functions of muscles?
Skeletal motion Skeletal stability Force production Fluid control
50
What are the 3 muscle types?
Smooth Skeletal Cardiac
51
What are smooth muscles?
autonomic (involuntary) EX: liver function: involuntary control of internal organs and vessels location: walls of hollow organs examples: stomach, intestines, blood vessels, bladder
52
What are skeletal muscles?
somatic (voluntary) EX: bicep function: voluntary movement of the body location: muscles attached to bones examples: biceps brachii, quadriceps, hamstrings
53
What are cardiac muscles?
autonomic / somatic EX: heart function: pumps blood through the body location: found in the heart example: myocardium
54
How are muscles organized?
Organized in agonist-antagonist pairs example: with a flexed arm, bicep is agonist (contracted) and tricep is antagonist (relaxed)
55
What are agonists?
muscle causing movement
56
What are antagonists?
muscle opposing agonist
57
Decribe how muscles contract
caused by the binding/unbinding of two protein molecules: actin and myosin. Myosin binds to actin and ratchets up (sliding), requires energy (ATP)
58
Muscles only ______
contract
59
What are the 2 important mechanical properties of muscles?
length-tension relationship velocity-tension relationship
60
What are length-tension relationships?
Peak muscle force (strength) depends on muscle length (posture)
61
What is the Sliding Filament Theory?
Efficiency depends on the overlap of actin and myosin chains, just right at resting length; peak muscle force (strength) depends on muscle length (posture)
62
What are velocity-tension relationships?
Capacity for force production depends on velocity Power = velocity * force
63
List the 2 muscle fiber types
Type I Type II
64
What are Type I Muscle Fibers?
slow, quick to fatigue, high force ex: marathon runners
65
What are Type II Muscle Fibers?
fast, fatigue resistant, low force ex: sprinters/strength training
66
What do type I and type II fibers differ in terms of?
maximum tension fatigue resistance aerobic and anaerobic capacities use in different tasks peak force generation prolonged force generation
67
What does muscle fatige depend on?
sequence and duration of contractions
68
Explain the Rohmert curve
Static endurance time vs. % effort As the percentage of maximum effort increases, the time a person can hold a static contraction (endurance) decreases exponentially The harder you hold a static force, the less time you can hold it
69
How does the Rohmert curve affect design?
Key idea: Static endurance decreases as exertion level increases, so designs must minimize sustained effort to prevent fatigue and injury. avoid static muscular loads, especially high ones minimize tasks requiring sustained muscle contraction (e.g., holding tools up without support) design tasks and tools to keep exertion low encourage: - neutral postures - use of supports and armrests - grip aids or mechanical assistance - task variation and micro breaks to reduce static load
70
What are the 4 affects aging has on muscles?
loss of muscle mass general decrease in muscle capacity/strength selective loss of type II fibers - less force, but maintain endurance loss of innervation (nerve cell damage)
71
What can help reverse some changes that aging has on muscles?
training
72
What do muscles require?
energy to be present
73
What is anthropometry?
Branch of science that attempts to describe the physical dimensions of the human body (human-measure)
74
What are the goals of anthropometry?
reliable methods for measuring (and predicting) human anthropometric parameters evaluate variance in anthropometric data that affect workplace design and tool design use anthropometric data in biomechanical models
75
What are the 2 types of anthropometry?
Physical and Functional
76
What is physical anthropometry?
structural, static addresses basic physical dimensions of the body ex: eye height, sitting measurement
77
What is functional anthropometry?
concerned with physical dimensions of the body relevant to activities or tasks ex: forward grip reach measurement
78
Why must caution be taken when combining body segment dimensions?
Caution must be taken when combining body segment dimensions because body parts do not scale proportionally across individuals, and combining segment measurements from different people can lead to misleading or unrealistic total body sizes. because every individual is different
79
Describe a stress-strain curve
if you apply a big enough stress on a material, it crosses the elastic region and is permanently deformed elastic region: material returns to original size/shape once stress is removed plastic region: permanently deformed by stress
80
How can Fitts' Law inform touch screen interface design for smartphones?
Fitts' Law dictates that larger and closer targets are easier and quicker to hit we can use this principle to place frequently used UI elements in more accessible areas think of one-handed mode or how we can create interfaces while minimizing finger travel distance
81
List 3 ways to design for population variance
Design for extremes Design for average Design for adjustability
82
What does design for extremes mean?
design for the largest or smallest users in the population (often 5th or 95th percentile) purpose: ensure everyone in the population can use the design ex: doorway height should accomodate the 95th percentile male
83
What does design for average mean?
design based on the average (50th percentile) user ex: fixed furniture like classroom chairs
84
What does design for adjustability mean?
provide range of adjustment to accommodate as many users as possible ex: car seat and steering wheel
85
How do you calculate population percentiles and designing for extreme values?
z =(x - μ)/σ
86
How do you calculate designing for average values?
x=μ +- Za*σ
87
Justify what to do with each step in anthropometry
1. Define the Design Problem and Dimensions: ensures the design targets the right problem; avoids measuring irrelevant body parts or creating an unfit product. 2. Identify the Target Population: ensures data and design fit the actual people who will use the product 3. Choose Anthropometry Database: Guarantees the design is based on accurate, statistical data. Using the wrong data leads to systematic design failure for the user group. 4. Select Design Cases: ensures the design fits extremes and the average, not just single dimensions. 5. Use Cases in Design & Evaluation: accommodates the intended users and validates the entire process before manufacturing.
88
Define work measurement
a productivity improvement tool involves the use of engineered labor standards to measure and control the amount of time required to perform a specific task or tasks
89
What are the 4 reasons work is measured?
to discover and eliminate lost or ineffective time to establish standard times for performance measurement to measure performance against realistic expectations to set operating goals and objectives
90
What does work measurement help to uncover?
non-value-added areas of waste, inconsistency, and non-standardization that exist in the workplace ways to make work easier and to produce products or services more quickly and economically
91
What are the 4 work measurement techniques?
Time Study Predetermined Time Systems Standard Time Data (Standard Data) Work Sampling (Statistical Sampling Theory)
92
What is time study?
Time Study uses real-time direct observation and timing; it is accurate for short, repetitive tasks but labor-intensive and intrusive. direct observation of task time watch worker perform job -> time elements -> apply performance rating + allowances
93
Pros and cons of time study
pros: accurate for repetitive tasks cons: time-consuming, disrupts work, requires trained observer
94
What is predetermined time systems?
Predetermined Time Systems assign standard times to basic human motions, offering high accuracy without observing workers, but require detailed analysis and training. pre-built database of time values for basic motions break job into basic motions (reach, grasp, move) -> assign motion times -> sum
95
Pros and cons to predetermined time systems
pros: very accurate, no need to observe worker, promotes method improvement cons: very detailed & time-insensitive, requires expertise
96
What is standard time data?
Standard Time Data reuses previously established time values, allowing fast application to similar jobs but depends on having reliable data and comparable tasks. reuse past time standards for similar tasks use previously established times for task elements instead of re-timing
97
Pros and cons of standard time data
pros: efficient, fast setup once library exists cons: requires strong database; accuracy drops if tasks vary
98
What is work sampling?
Work Sampling estimates time distributions by observing workers at random intervals; it is efficient for long or varied tasks but less precise for short repetitive cycles. statistical sampling of work vs idle time observe at random intervals -> estimate proportion of time in task categories
99
Pros and cons of work sampling
pros: low cost, great for linger and non-repetitive work, minimal disruption cons: less accurate for short-cycle tasks, requires large sample sizes
100
How does worker selection affect time study data collection?
the worker selected must be a properly trained, experienced, average-performing employee, because choosing someone unusually fast or slow would produce unrealistic and biased time standards
101
What worker should be selected for a time study?
average worker
102
What is Normal Time for a time study?
time an experienced worker should take
103
What is Observed Time for a time study?
time recorded from stopwatch
104
What is the Operator's Rating for a time study?
100% = standard performance higher value for expert, lower for novice
105
How do you calculate normal time?
NT = OT * (R/100)
106
What is standard time?
normal time is increased to account for allowances
107
How do you calculate standard time?
ST = NT * (1 + work allowance) OR ST = NT / (1 - shift allowance)
108
Why are allowances accounted for in a time study?
It accounts for reduction in work time beyond the workers control Allowances are included in a time study to ensure the standard time reflects real working conditions. Workers cannot perform at a constant pace without interruption; they need breaks, experience fatigue, and may face unavoidable delays. allowances are added to the normal time so the standard time is realistic, fair, and sustainable, preventing overwork and supporting productivity.
109
What are the 4 types of allowances?
Personal Fatigue Delay Special
110
What are predetermined time systems (PTS)?
to increase productivity for a particular task: - broke work into therbligs (elements) - then assign time values to the elements - times for elements are added to obtain a total time PTS are based on the concept that there are basic, universal units of work with standard amounts of time
111
What are assumed in predetermined time systems?
independence and additivity
112
How does PTS differ from time studies?
in methodology; TSs uses empirically collected data i.e., real-time measurements using a stopwatch for instance, whereas PTSs use predetermined time standards based on the motions.
113
What are Therbligs and who coined the name?
Frank and Lillian Gilbreth coined the term A reversal of the name of the scientist who established them (Gilbreth). Set of fundamental motions required for a worker to perform a manual operation or task Therbligs are independent and additive work motions that are assigned time values
114
What is a TMU?
1 Time measure unit (TMU)= 0.0006 minutes
115
What are some benefits and limitations of PTSs?
benefits: it can accurately predict task times limitations: concern with cost of analysis, analyst judgment could be a problem
SYS 3023
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