monday, august 30 –homework due today: check out one web site related to biomechanics of exercise...
TRANSCRIPT
• Monday, August 30– Homework due today:
• 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?
– Topics for today’s lecture• 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)
Vector Summation and Composition
• Kinetic vector quantities – force weight, pressure, specific weight &
torque
• Kinematic vector quantities– Displacement, velocity & acceleration
• Scalar quantities– Mass, volume, length & speed
Vector Composition (Addition)
• Resultant vector
• “Tip-to-tail” vector composition
Vector #1
Vector #2
Resultant vector
Vector Addition Problems found in human motion analysis
• Combining forces– Net effect of two forces applied to any object– What is maximum safe speed for a curve?
• Centrifugal force, frictional force, & gravity
– What makes a curveball curve?• Wind force and weight
• Combining velocities– In crossing a river, what direction is best?
• Velocity of water and swimmer
– In aviation, correcting for wind• air speed and ground speed
Vector Resolution(Finding components)
Vertical
Horizontal
Example: A ball is thrown into the air
Resultant
Vector resolution problems found inhuman motion analysis (pp 76-81)
• Projectile motion situations– Find horizontal velocity– Find vertical velocity
• Friction problems – Find horizontal force component (Friction)– Find vertical component (Normal)
• First step in adding, or combining vectors– When more than one force is acting on an object– When adding velocity vectors
Trigonometric Solution of Vector Problems
• A more accurate procedure for quantitatively dealing with vector problems
Vector resolution:
Vert comp = F•sinΘHoriz comp = F•cosΘ
Θ
Vert comp = F•sin•ΘHoriz comp = F•cos•Θ
Example: If F = 890N (200 lb) and Θ = 75 º, then: Fvert = 860 N, Fhoriz = 230 N
Θ
Θ Θ
Final step – what is the effect of the sum of these vectors?If the vectors are forces, then the net effect is to accelerate the object: a = F/m
Homework assignment on Vector Summation
• Handout homework problem to turn in Wed, Sept 1
• Self-test problems (do not turn in):– Additional problems, p 81 # 4 and 5
COM Concepts and calculation procedures
• Objectives– To review concept of COM– To review reasons for studying COM– To review calculation method for calculating COM of
human body
Why study Center of Mass of Human Body?
• It simplifies the movement of the complex system so that we can understand its overall motion
• It allows us to easily consider the effect of net external forces (F = ma; a = F/m)
• Example of important issues related to COM– Is COM different for children and adults in a way that
affects movement?– Can an athlete really “hang in the air”– Is COM different for males and females in a way that
affects movement?
COM/COG Calculation Method (pp 436-445: Kreighbaum pp 116-123, 586-587)
• Concept of balancing segmental torques
• Segmental Calculation of COM – General calculation method– Information needed
• Proportionate mass of each segment (p 520)
• location of COM of each segment (p 521)
– Homework problem (handout in class)
Segmental concept of center of mass
–Information needed
•Proportionate mass of each segment (p 520)
•location of COM of each segment (p 521)
Summary• Chapter 3 introduced basic concepts related to kinetics:
– Several types of mechanical loads act on the human body.– The distribution of force within a body structure is termed
mechanical stress.– Vectors quantities have magnitude & direction– Vector problems may be solved by a graphic or a
trigonometric approach. – Calculation methods for vector summation and resolution of
vectors were presented– Center of mass (COM) concepts were reviewed– Calculation methods for total body COM were presented
Next Class – Wednesday, Sept 1
• Read text, pp 329-347• Take web-based quiz for Chapter 10 • Objectives
– Review characteristics of projectile motion – Review factors influencing projectile motion – Present and explain calculation methods for analyzing projectile
motion
• Homework – due Wednesday, Sept 8– Problems 7,9,10 on page 347