Fundamentals of Biomechanics

L-20 FUNDAMENTALS OF BIOMECHANICS
LAB ACTIVITY 7B
CALCULATING CENTER OF GRAVITY USING ANGULAR KINETICS
The purpose of this lab is to improve your understanding of torque, summation of torques,
and center of gravity. Torque is a useful kinetic variable explaining the causes of human
movement because of the angular motions of joints. Locating the center of gravity of an object
and tracking its motion is useful in understanding how the force of gravity affects
movement and balance. The reaction board method will be used with the angular analog
and static form of Newton’s second law (ΣT = 0). Remember that torque (T) or moment of
force is the product of the force and the perpendicular distance between the line of action
of the force and the axis of rotation (T = F d ⊥ ).
BACKGROUND READING
Chapter 7: “Angular Kinetics”
Gard, S. A., Miff, S. C, & Kuo, A. D. (2004). Comparison of kinematic and kinetics methods
for computing the vertical motion of the body center of mass during walking. Human
Movement Science, 22, 597–610.
TASKS
1. Estimate the height of your center of gravity as a percentage of your height: _____.
2. Record your height and weight. Measure the length of the reaction board from one supporting
edge to the other.
3. Measure the reaction force lying on the reaction board in your normal standing position,
and in another sport/activity relevant position of interest to you. Think about where you
should you put your feet to make the calculation easier to express relative to your body.
4. Perform calculations to calculate the location of your center of gravity and answer the
questions.
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