Hick's and Fitts' Law
Define Hick's Law and its variables.
RT = a + b*log2(N) where n = # choices and H = amount of information that must be processed, measured in BITS.
List two functions of the connective tissue.
1. Force transmission and movement
2. Metabolism
3. Defense
4. Storage/buffer
What are the two types of anthropometry?
Physical: physical dimensions of the body.
Functional: physical dimensions relative to activities or tasks.
Define therbligs along with an example.
A reversal of the name of the scientists who established them (Gilbreth). Therbligs are independent and additive work motions that are assigned time values.
Muscles only ____________ (Jan Swammerdam, 1663)
Define Fitts' Law and its variables.
As ID increases, MT linearly increases.
ID = log2(2D/W)
What's the difference between tendons and ligaments?
Tendons: muscle to bone
Ligaments: bone to bone
List the three ways to design for population variance.
Design for extremes: door height should accommodate 95th percentile male.
Design for average: height of visual display
Design for adjustability:
List the three allowances typically accounted for.
Personal: same for all tasks (5%)
Fatgiue: based on task, related to physical demands (4%)
Delay: based on interruptions, breakdowns (3%)
Give an example of an agonist-antagonist muscle pair.
Biceps and triceps.
How can Fitts' Law inform touchscreen 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.
Define stress, strain, and describe the stress-strain curve.
Stress: force/unit area that results from an applied load
Strain = physical deformation response of a material
If you apply a 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.
Assume the mean of height for the U.S. population is 66.2 in with a standard deviation of 3.6 in. (Refer to z-score table).
What is the height (stature) percentile of a person with a height of 69.4 inches?
z = (x – µ)/σ = (69.4 – 66.2)/3.6 = 0.88 --> 81.06 = 81st percentile
Explain how worker selection affects time study data collection. State what worker should be selected
Should select average worker.
State the three types of muscle types.
Smooth: involuntary nervous control, like your liver
Skeletal: voluntary nervous control, like your biceps
Cardiac: both
For a website with a 4 s base reaction time and a processing speed of 0.2 s per option, what is the reaction time to choose between 8 options?
a = 4; b =0.2; n = 8
RT = 4 + 0.2 log2(8) = 4.6 s
List three factors that increase the risk of joint injury.
Aging, inflammation, previous injuries, loss of muscle mass, excess weight
Assume the mean of height for the U.S. population is 66.2 in with a standard deviation of 3.6 in. (Refer to z-score table).
What height is needed to accommodate a 99th percentile male?
z = (x – µ)/σ --> x = z0.99 * σ + µ = 2.33 * 3.6 + 66.2 = 74.6 in
How do PTSs differ from time studies?
PTSs 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.
Explain the velocity-tension relationship.
Capacity for force production depends on velocity.
Power = velocity * force.
Elise should choose between two button designs; the first has a target distance of 3 and target width of 4, whereas the second has a target distance of 5 and target width of 4. Which button yields lower MT?
Assume: a = 1.2 and b = 3
MT1 = 1.2 + 3*log2(2*3/4) = 2.95 s
MT2 = 1.2 + 3*log2(2*5/4) = 5.16 s
Choose button 1.
List the three types of joints with an example of each joint.
Synovial: most common, like wrist, elbow, knee
Cartilaginous: some motion, high load bearing e.g., spine
Fibrous: immobile e.g., skull
Assume the mean of height for the U.S. population is 66.2 in with a standard deviation of 3.6 in. (Refer to z-score table).
What height range will accommodate 90% of males?
z = (x – µ)/σ --> x = µ ± z0.05 * σ = 66.2 ± 1.64 * 3.6 --> [60.3, 72.1]
What is the formula for:
(a) Normal time
(b) Standard time
NT = OT x (R/100)
ST = NT x (1 + Work Allowance)
Explain the length-tension relationship.
Peak muscle force (strength) depends on muscle length (posture)
Sliding Filament Theory – efficiency depends on the overlap of actin and myosin chains: just right at resting length; too short = interference; too long = not enough overlap