Week 2 Overview

1
Week 2 Overview

• Wednesday, August 25
• Read Hall, Ch 3 on Kinetic Concepts
• Take web-based practice exam http//www.mhhe.com/h
  all4e
• Review Powerpoint slides
• 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)
• Monday, August 30
• 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 Monday, August 30
• 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?

2
Kinetic Concepts 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

3
Basic Concepts Related to Kinetics

• Pressure Force/Area
• Volume LWH
• Density Mass/Vol
• Torque Fd
• Impulse Ft

• Inertia
• Mass
• Force
• Free body diagram
• Center of Gravity
• Weight

4
Common Units for Kinetic Quantities

• Quantity Symbol Metric Unit English Unit
• Mass m kg slug
• Force F
  N lb
• Pressure P Pa
  psi
• Volume (solids) V m3
  ft3
• (liquids)
  liter gallon
• Density ?
  kg/m3 lb/ft3
• Torque T N-m
  ft-lb
• Impulse N
  s lb s

5
Four Properties of forces
Center of Gravity of different objects
6
Free body diagrams
7
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
• Solution
• Wanted Answer
• Pressure 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

8
Mechanical Loads on the Human Body

• Compression
• Tension
• Shear
• Torsion

9
Bone loading modes Compression pushing
together Tension pulling apart Torsion
twisting Shear cutting across
10
Cutting across
11
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)
• Youngs Modulus of elasticity, or stiffness
• Yield point (elastic limit)
• Strength

12
Load-deformation relationship
Stress-strain curve
13
Repetitive vs. Acute Loads

• Repetitive loading
• Acute loading
• Macrotrauma
• Microtrauma

14
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

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Force Plates Measurement of ground reaction
forces