 # EXNS 6223 Penn State University Torque and Force Balance Questions Exam

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EXNS 6223

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Biomechanical Analysis EXNS 6223 Comprehensive Exam Open Book and Notes Name: DOMINIC RONDINELLI All parts in the question must be completed for you to receive full credit. 1. You’ve been invited to take part in a study in a biomechanics lab. The first thing you are shown is the general setup of the lab, with force plates and cameras to record every static and dynamic measurement. a. What information can we record from the force plates? Force plates are useful in recording information of ground reaction forces generated by a body standing on or moving across. They can quantify balance, gait, and other parameters of biomechanics. b. You stand on one of the force plates so we can calibrate it before starting the study. The plate measures 30 feet on each side. Let’s assume your weight is 180 pounds and you are standing 5 feet from Sensor A. One of the researchers places a 10 pound cube 15 feet from Sensor B. Solve for all torques and forces from Sensor A and Sensor B. Measurement on each side: 30 ft Weight: 180 pounds Dist from Sensor A: 5 ft Weight of Cube: 10 pound Dist from Sensor B: 15 ft Find: all T and F from sensor A and B Solution: Ffp= total calc force applied to the FP Mfp= total calc reference moment resulting from forces applied to the force plate According to Netwon’s 2nd law: sumF= mdv/dt For calc. of vertical fores jump height, only the forces acting on the body in the y direction need to be considered. The two forces are the ground reaction forces (f2 (t)) and the forces due to the mass of the body (mg) sumFy= mdv2/dt= Fy(t)-mg the vert. impulse can be calc by integrating the measured vertical ground reaction forece until the point of takeoff, when the forces go to zero. T1 is the time before takeoff when standing on the plate and t2 is the take off time. The center of mass velocity at takeoff, vt0, is give by : vt0= 1/m x Fy(t) – mg (dt) After substituting values : FxFy=1000 N/V, Fy= 2000 N/V. Mx= 600 N-m/v ; My= 500 N-m/V ; Mz= 300 N-m/v T= Fx*moment arm T=8000x1500 = 12 x 10^6 Nm c. What assumptions do we make for part b? -each segment is treated as rigid with a fixed length through movement. -each segment can be modeled as having a point mass that is fixed relative to the geometry of the rest of the segment (center mass) -mass moment of inertia remains constant d. Now off the plate, approximately 100 yards away, the researchers want you to run towards the cube on the force plate. You start running at 10 mph and stop your movement in 0.88 seconds. What force did you encounter? F=ma. 10# = 4.53 kg. 10 mph=4.47 ms-1 F = 4.53 x 4.47/0.88 F = 23.01 N e. The researchers are pleased with the data recorded but want you to repeat the run with the location of the force plates modified for what purpose? Significant differences can be found for peak vertical impact forces and their timing, and for the 3 lower limb segment angles at the start of the force plate contact. These results have implications for human gait studies, which require subjects to target the force plate. Targeting maybe acceptable depending on the variables to be analyzed. This is the purpose of repeating the run with the location of the force plates modified. f. In addition to understanding the forces related to running, you repeat the experiment while walking. With your foot ready to come off the plate, what do the researchers notice with the vertical ground reaction force, and why? The vertical ground reaction force is the force exerted by the ground on the body within contact with it. Vertical ground reaction force influences the joints. The researchers found that a large magnitude of forces is transmitted by the muscles through the tendons across the joint when the foot comes off the plate. Vertical ground reaction force can be measured by force plates through piezoelectric or strain gauge.
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Biomechanical Analysis
EXNS 6223
Comprehensive Exam
Open Book and Notes

Name: DOMINIC RONDINELLI

All parts in the question must be completed for you to receive full credit.

1. You’ve been invited to take part in a study in a biomechanics lab. The first thing you
are shown is the general setup of the lab, with force plates and cameras to record
every static and dynamic measurement.
a. What information can we record from the force plates?
Force plates are useful in recording information of ground reaction forces generated
by a body standing on or moving across. They can quantify balance, gait, and other
parameters of biomechanics.
b. You stand on one of the force plates so we can calibrate it before starting the
study. The plate measures 30 feet on each side. Let’s assume your weight is
180 pounds and you are standing 5 feet from Sensor A. One of the
researchers places 10-pound cube 15 feet from Sensor B. Solve for all torques
and forces from Sensor A and Sensor B.
Force on sensor A = Normal force from ground due to the person’s weight =
weight of the person = 180 pound-force
Force on sensor B = Normal force from ground due to the cube’s weight =
weight of the cube = 10 pound-force
Torque on sensor A = Force on sensor A × Distance from the man = 180 × 5 =
900 pound-foot
Toque on sensor B = Force on sensor B × Distance from the cube = 10 × 15 =
150 pound-foot
Forces in the horizontal plane are 0 for both sensors since there is no
horizontal shear stress (such as friction) being experienced in this case. All
forces are in the vertical direction.
c. What assumptions do we make for part b?
...  Anonymous
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