fw275 biomechanics
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Exploring Biomechanics
Biomechanics: bio means “life” Study of the actions of forces Term first used 1970’s Includes both internal forces produced by
muscles and external forces that act on the body Biomechanics human movement is one sub
discipline of exercise science
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Exploring Biomechanics Biomechanics
Academic backgrounds: zoology, medicine, engineering, physical therapy
Common interest in biomechanical aspects of the structure and function of living things
Undergraduate course Usually requires prerequisite courses Focusing on forces acting on the human body Biomechanics commonly a quantitative field of study Strong math, computer applications and problem solving
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History of Biomechanics
Aristotle (384-322 B.C.)
Archimedes (287-212 B.C.)
Galen (131-201 A.D.) Leonardo da Vinci
(1452-1519) Galileo (1564-1642)
Giovanni Alfonso Borelli (1608-1679)
Isaac Newton (1643-1727) Eadweard Muybridge
(1831-1904) Julius Wolff (1836-1902) Christian Wilhelm Braune
(1831-1892) & Otto Fischer (1861-1971)
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Basic Biomechanics--Kinematics
Kinematics The form, pattern, or sequencing of movement with
respect to time Qualitative
Involving nonnumeric description of quality Quantitative
Involving the use of numbers Kinematic analysis often requires the use of both
visual description and quantitative measurement
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Basic Biomechanics--Kinematics
Kinematic quantities: distance, displacement, speed, velocity, acceleration
Vector quantities have both size and direction Displacement, velocity, acceleration
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Basic Biomechanics--Kinematics
Linear displacement Change in linear position
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Basic Biomechanics--Kinematics
Angular displacement Change in the angular position or orientation of a
line segment
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Basic Biomechanics--Kinematics Angular--most human movement requires
angular quantities Rotation around a central line or point Primarily rotational motion occurs at joints
Linear velocity Rate of change in linear position
Angular velocity Angular displacement divided by the time interval
which displacement occurs
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Basic Biomechanics--Kinematics
Acceleration Angular acceleration
Does not take into account particular circumstances or rules when faced with a moral problem
With every moral situation, there is a blank slate and each case must be viewed independently
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Basic Biomechanics--Kinematics
Biomechanics use quantitative kinematics to research differences between skilled performers and non-athletes. Examples: Runners stride length & frequency Swimmer’s stroke rate & length Track events velocity of takeoff High jumpers vertical displacement Basketball angle of projection, angle of release Throwing events aerodynamics of flight path Swinging (bat, racquet) timing, project speed and
angle
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Basic Biomechanics--Kinematics
Skilled performers move body segments at high rate of angular velocity
Most biomechanical studies of human kinematics involve non-athletes: Infant through maternity developmental stages Adapted P.E. kinematic patterns with motor disorders Therapeutic uses to aid in recovery of
injuries/surgeries
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Basic Biomechanics--Kinematics
Quantitative kinematic analyses often use: High-speed cinematography videography
Reflective markers Digitizing
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Kinetics Study of the action of forces
Force The product of mass and acceleration Push or pull acting on a body
Vector quantity: magnitude, direction & point of application to a body
Free body diagram First step used when analyzing actions Body, body segment or object of interest
Basic Biomechanics--Kinetics
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Basic Biomechanics--Kinetics
Force rarely acts in isolation Net force
Overall effect of many forces acting on a body Vector sum of all the acting forces
Net force zero = acting forces balanced in magnitude and direction
Net force present = body moves in the direction of the net force with acceleration
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Basic Biomechanics--Kinetics
Torque The rotary effect of a force
Torque quantified The product of force (F) and the perpendicular
distance (d┴) from the force’s line of action to the axis of rotation T = F d┴
The greater the force, the greater the tendency for rotation
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Basic Biomechanics--Kinetics
Inertia--Sir Isaac Newton Tendency of a body to resist a change in its
state of motion Resistance to acceleration Inertia has no units of measurement Amount of inertia a body possesses is
directly proportional to its mass More massive an object is, the more it tends
to maintain its current state of motion
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Basic Biomechanics--Kinetics
1st law of inertia A Body will maintain a state of rest or
constant velocity unless acted on by an external force that changes the state
A motionless object will remain motionless unless there is a net force acting on it
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Basic Biomechanics--Kinetics
Inertia is influenced by mass (m) and distribution of mass in the body
Mass distribution is characterized by the radius of gyration (k)
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Basic Biomechanics--Kinetics Newton’s 2nd law--law of acceleration
A force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body’s mass
The greater the amount of force applied, the greater the speed
F=ma Angular motion, the law becomes:
When a torque acts on a body, the resulting angular acceleration is in the direction of the torque and of a magnitude inversely proportional to its moment of inertia
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Basic Biomechanics--Kinetics
Newton’s 3rd law--law of reaction For every action, there is an equal and opposite
reaction
In terms of forces: When one body exerts a force on a second, the
second body exerts a reaction force that is equal in magnitude and opposite in direction on the first body
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Basic Biomechanics--Kinetics Ground reaction forces
Are measured during gait, each contact the foot makes with floor is analyzed
Walking, running patterns throughout development stages using force platforms
Magnitude of the vertical component of the GRF during running is generally two to three times the runner’s body weight
Runner’s are classified as rearfoot, midfoot, or forefoot strikers
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Basic Biomechanics--Kinetics
GRF is an external force acting on the human body
Magnitude and direction have implications for performance in many sporting events High jumper’s Baseball pitching Golf
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Basic Biomechanics--Kinetics
Friction is a force that acts at the interface of surfaces in contact in the direction opposite the direction of motion or impending motion
Units of force (N) The size of the friction force is the product of
the coefficient of friction (µ) and the normal (perpendicular) reaction force (R).
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Basic Biomechanics--Kinetics Factors influencing the value of friction µ
Relative roughness and hardness of the surfaces Type of molecular interaction between surfaces
Greater the molecular interaction, the greater is the value of µ
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Basic Biomechanics--Kinetics
Normal reaction force (R) Sum of all acting vertical forces (usually body’s
weight)
Altered magnitude R Increased or decreased When friction is altered, how does this change
motion?
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Basic Biomechanics--Kinetics Altering the coefficient between two
surfaces can change friction Use of gloves, thin wax…
Important daily influence to prevent slippage
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Basic Biomechanics--Kinetics Momentum (M) is a vector quantity
The quantity of motion that an object possesses mechanical quantity important in collisions
Linear momentum Product of an object’s mass and its velocity Body with zero velocity has no momentum What should the momentum be during most
weight training exercises?
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Basic Biomechanics--Kinetics
Impulse Product of a force and the time interval over which
the force acts Impulse = Ft Impulse can change momentum
Impulse and momentum Changes in momentum depend not only on the
magnitude of the acting external forces but also on the length of time over which each force acts
When impulse acts on system, the result is a change in the system’s total momentum
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Basic Biomechanics--Kinetics Angular momentum (H)
Quantity of angular motion possessed by a body, measured as the product of moment of inertia and angular velocity
H product of angular inertial property (moment of inertia) and angular velocity
Linear momentum Product of the linear inertial property (mass) and liner velocity
Liner motion: M – mvAngular motion: H = Iw
or: H = mk2
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Basic Biomechanics--Kinetics
Factors affect magnitude of a body’s angular momentum
Mass (m) Distribution of that mass with respect to axis of rotation Angular velocity of the body (w)
If body has no angular velocity; it has no angular momentum
Mass or angular velocity increases; angular momentum increases proportionally
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Basic Biomechanics--Kinetics Factor that most dramatically influences angular
momentum Distribution of mass with respect to the axis of rotation Why? Angular momentum is proportional to the momentum
result from multiplying units of mass, units of length squared, and units of angular velocity
Kg ·m2/s
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Basic Biomechanics--Kinetics Angular impulse
Change in angular momentum equal to the product of torque and time interval over which the torque acts
Angular impulse generates a change in angular momentum
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Basic Biomechanics--Fluid Mechanics
Fluid (interchangeably with liquid) Is any substance that tends to flow or continuously
deform when acted on by a shear force Both gases & liquids are fluids
Archimedes Principle The magnitude of the buoyant force is equal to the
weight of the fluid displaced by the body If magnitude of weight is greater than buoyant force,
the body sinks, moving downward in the direction of the net force
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Basic Biomechanics--Fluid Mechanics
Buoyancy is studied in relation to floatation of human body in water
Difference in floatability is function of body density
Density of bone and muscle is greater than the density of fat
What changes with floatation when a person holds inspired air in the lungs?
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Basic Biomechanics--Fluid Mechanics
Orientation of the body as it floats in water is determined by the relative position of the totally body center of gravity relative to the total body center of volume
What is center of gravity?
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Basic Biomechanics--Fluid Mechanics COG is the point around which the body’s
weight is balanced in all directions Center of volume and Center of gravity vary
depending on body shape and size
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Basic Biomechanics--Fluid Mechanics Drag
Generally, a resistance force: A force that slows the motion of a body moving
through a fluid Theoretical square law
The magnitude of the drag force increases approx with the square of velocity Effect seen with high velocity sports: cycling, speed
skating, downhill skiing, bobsled, luge 3 types of drag
Skin friction/surface drag Form drag/profile drag Wave drag
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Basic Biomechanics--Fluid Mechanics
Form drag
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Basic Biomechanics--Fluid Mechanics
Wave drag
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Basic Biomechanics--Fluid Mechanics
Force that acts perpendicular to fluid flow is lift
Lift can assume any direction (not just vertically upward) Determined by direction of fluid flow and
orientation of body Can be generated by foil
Shape capable of generating lift in the presence of a fluid flow
Human hand during swimming
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Basic Biomechanics
The study of biomechanics covers many other topics that help us to better understand human movement in relation to forces acting on the body, joint movements and forms of motion
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Professional Organizations
Advantageous for students to consider student memberships with professional organizations in their chosen field of sport science study
Biomechanics has many supported journals Memberships include discounts: journal
subscriptions, conference fees and opportunities for students to interact with professionals
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Professional Organizations
American Society of Biomechanics Canadian Society of Biomechanics European Society of Biomechanics International Society of Biomechanics International Society of Biomechanics in Sport Mulit-disciplinary organizations
American College of Sports Medicine American Alliance for Health, Physical Education,
Recreation and Dance