Week 2 Overview Monday, February 2 –Read Hall, Ch 3 on Kinetic Concepts –Take web-based practice...

Week 2 Overview• Monday, February 2

– Read Hall, Ch 3 on Kinetic Concepts– Take web-based practice exam http://www.mhhe.com/hall4e– Review Powerpoint slides (will be posted by Friday 5:00 PM)– Self-test Intro problems (pp 80-81): 1,2,5,6,7,9,10 (select one to do in class)– Self-test additional problems (p 81): 1,,7)

• Wednesday, February 4– Vector resolution and summation (pp 76-80)– Center of mass – what it is and how to determine it in the human body (pp 436-442)– Homework due on Wednesday:

• Check out one web site related to biomechanics of exercise or sport (some are listed on p 25) and submit a one-page description of the site that includes:

– Internet address– Title or purpose of site – who is the intended audience?– Is the site exercise or sport oriented?– Is information of use to you in any way? If so, how? If not, for what type of audience would it be of value?

Objectives• Define and identify basic concepts related to

kinetics: inertia, mass, force, center of gravity, weight, pressure, volume, density, torque, and impulse

• Identify and describe the different types of mechanical loads that act on the human body

• Identify and describe the uses of available tools for measuring kinetic quantities

Basic Concepts Related to Kinetics

• Inertia

• Mass

• Force– Free body diagram

• Center of Gravity

• Weight

• Pressure: Force/Area

• Volume: LWH

• Density: Mass/Vol

• Torque: Fd

• Impulse: Ft

Common Units for Kinetic Quantities

Quantity Symbol Metric Unit English UnitMass m kg slugForce F N lbPressure P Pa psiVolume (solids) V m3 ft3

(liquids) liter gallonDensity kg/m3 lb/ft3

Torque T N-m ft-lbImpulse N • s lb • s

Four Properties of forces:

Center of Gravity of different objects:

Free body diagrams:

Sample Problem 1 on pressure (p 67)

Is it better to be stepped on by a women wearing a spike or by a court shoe?

Known: wt = 556 N As = 4 cm2 Ac = 175 cm2

SolutionWanted: AnswerPressure exerted by the spike heel p = 139N/cm2

Pressure exerted by the court shoe p = 3.8 N/Cm2

Formulas: p = F/A 43.75 times more pressure

Mechanical Loads on the Human Body

• Compression

• Tension

• Shear

• Torsion

Bone loading modes: Compression – pushing together Tension – pulling apart Torsion – twisting Shear – cutting across

Cutting across

The Effects of Loading• Deformation

• When an external force is applied to the human body, several factors influence whether an injury occurs– Magnitude and direction of force– Area over which force is distributed– Mechanical properties of tissue (stress-strain curve)

• Young’s Modulus of elasticity, or stiffness• Yield point (elastic limit)• Strength

Load-deformation relationship:

Stress-strain curve:

Repetitive vs. Acute Loads

• Repetitive loading

• Acute loading

• Macrotrauma

• Microtrauma

Tools for Measuring Kinetic Quantities

• Electromyography (EMG)– To study neuromuscular function– Website: Surface electromyography systems, emg

electrode, emg acquisition analysis software

• Dynamography– Primarily employed in gait research– Starts, takeoffs, landings, baseball & golf swings, and

balance

Force Plates – Measurement of ground

reaction forces