Fluid Mechanics
In what direction does the drag force act?
the opposite direction to the relative motion of an object through a fluid
If an object with a specific gravity of 1.07 is immersed in water, will it sink or float?
Sink
What term describes the deformation or change in shape of a material or tissue in response to an applied force?
Strain
Which of the following is an example of a biological structure showing plastic behavior?
a. A tendon returning to its original length after a small stretch
b. A ligament that tears and does not fully return to its original shape
c. A muscle contracting and relaxing normally
d. Bone experiencing normal loading without permanent deformation
b. A ligament that tears and does not fully return to its original shape
A swimmer swims at 2 mph in the opposite direction as a river current moving at 5 mph. What is the relative velocity of the swimmer?
7 mph
RV = 2 mph - (-5 mph) = 7 mph
At higher velocities, which type of drag will have the largest impact on the overall drag force?
Form drag
What principle states that a body submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces?
Archimedes' principle
What is the mechanical property that measures the stiffness of a solid material by calculating the ratio of stress to strain in the elastic region of deformation?
Elastic (Young's) Modulus
In a downward bending load, what type of stress is experienced in the bottom half of the analysis plane?
Compressive stress
The Achilles tendon is subjected to a large tension that results in a strain of 10%. If the unloaded tendon is 10.4 cm long, how much does it elongate?
1.04 cm
ε=ΔL/L0
ΔL=ε*L0
ΔL=0.10*10.4 cm = 1.04 cm
What is the phenomenon that causes the generation of a sidewise force on a spinning object moving through a fluid?
Magnus effect
Through what point on an object does the buoyant force act?
Center of volume
What is the name of the maximum stress a material can withstand before it begins to deform permanently?
Yield strength
Which biological structures are best designed to withstand compressive loads?
Bones
A gymnast is stretching and performs a hamstring stretch. If the hamstring has a resting length of 32 cm, and the athlete stretches to a length of 41 cm, what is the linear strain experienced by the hamstring?
28%
ε=(41−32)/32=0.28125
What type of flow occurs when molecules stay close to the surface of an object?
Laminar flow
What component of lift force has the largest influence on the overall lift experienced by the object?
Relative velocity
What are the three principal stresses?
Tension, compression, and shear
While tension and compression are considered axial stresses, shear stress is considered what type of stress?
Transverse stress
A tendon has an initial length of 0.3 m and a cross-sectional area of 0.0000014 m2. A load of F=600 N elongates the tendon by 1.2 mm. What is the Young’s modulus of the tendon?
107,000,000,000 Pa
Stress: σ=600N/0.0000014m2≈428,571,428 Pa
Strain: ε=0.0012/0.3=0.004
Young's Modulus: E=σ/ε; 428,571,428/0.004 = 107,000,000,000 Pa
What is the specific point on an object in a fluid where the total resultant force from the fluid acts?
Center of pressure
Which principle states that for a fluid in motion, an increase in its speed is accompanied by a decrease in its pressure, and vice versa?
Bernoulli principle
What type of materials will have the smallest elastic modulus?
a. Rigid and resistant to deformation
b. Flexible and easily deformed
c. Strong but able to stretch before breaking
d. Hard and brittle
b. Flexible and easily deformed
What is the name for the maximum stress a material can withstand before it begins to weaken and deform significantly?
Ultimate strength
When Simon rides his bicycle at 11 m/s, the drag force acting on him and his bicycle is 13 N. If he speeds up to 15 m/s, what will the drag force be?
24.2 N
The drag force is proportional to the square of velocity:
F2/F1 = (v2/v1)2
F2 = F1 (v2/v1)2
F2 = 13 (15/11)2 = 24.2 N