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Biomechanics

Examines the internal and external forces acting on the human body and the effects produced by these forces

Aids in technique analysis and the development of innovative equipment designs

Kinematics Study of Motion

The study of time and space factors of a body in motion

The variables used to describe motion are time, displacement, velocity, and acceleration

These variables are used to describe both linear and angular motion (angular displacement, angular velocity, and angular acceleration)

Kinematics Variables

• Time: a time interval calculated as the difference between the beginning and the end of two instants of time

• Displacement: length and direction of the path an athlete takes from start to finish

• Angular Displacement: direction of, and smallest angular change between, the rotating body’s initial and final position

• Velocity: displacement per unit of time

• Angular Velocity: angular displacement per unit of time

• Acceleration: rate of change of velocity

• Angular Acceleration: angular velocity per unit of time

Kinetics Study of Motion

Internal Forces: generated by muscles pulling via

their tendons on bones, and to bone-on-bone forces exerted across joint surfaces

Cause body segment movements

External Forces: acting from without, such as the

force of gravity or the force from any body contact with the ground, environment, sport equipment, or opponent

Affect total body movement

Focuses on the various forces that are associated with a movement

Types of Motion

Linear motion Angular motionGeneral motion

Linear Motion

When all parts of the body move the same distance, in the same direction, at the same time

Refers to movement of the body as a unit without individual parts of the body moving relative to one another

Rectilinear motion occurs when movement follows a straight line

Curvilinear motion occurs when the movement path is curved

Angular and General Motion

Angular Motion (rotation) Occurs when a body moves along a

circular path, through the same angle, in the same direction, and at the same time

The axis of rotation is the point about which movement occurs

All joint motions are angular motions

General Motion A combination of linear and angular

motion

Includes most athletic and many everyday activities

Causes of Motion

The only cause of motion of the human body is the application of an internal or external force

Force is any action, a push or pull, which tends to cause an object to change its state of motion by experiencing an acceleration

Constant Velocity occurs when an object is not accelerating

Linear Motion is caused by forces which act through a body’s centre of mass

Angular motion is caused by forces that do not go through the centre of mass

Linear motion results when the forces are applied through the centre of mass

Angular motion results when the forces are applied away from the centre of mass

Scalar and Vector Quantities

Scalar quantities have only magnitude i.e. length of time to run 100m

speed posted on a road sign (100km/h)

Vector quantities have magnitude and direction (force) - vectors are straight-line segments with one end defined as the tail and the arrow tip defined as the head.

tailhead

Adding of Vectors

The head of a vector points in the direction of the quantity the vector represents

Vectors can be added together using the head to tail method - to add vector B to vector A, an identical vector is drawn (same length

and direction) as vector B beginning at the head of vector A - the resultant vector is directed from the tail of vector A to the head

of vector B and represents the acceleration of the person/object

a

b+

a b

Resultant Resultant=

Calculating net external force using free body diagrams

Levers

• Simple machines that augment the amount of work done by an applied forceo Axis/Fulcrum (A) - A rigid body (i.e., long bone) that rotates about

a fixed point (i.e., joint)o Load (L) – Weight acting on the lever (i.e. weight of a limb

segment)o Effort (E) – point initiating movement (i.e. Insertion point of

muscle)

• Three classes of levers: a. first class (teeter-totter) b. second class (wheelbarrow) c. third class (shoveling snow)

Calculating Moments of Force Moment arm is the (perpendicular)

distance from the axis of rotation to where the force is being applied

Moment of force is the measure of a forces tendency to produce a rotation

influenced by the magnitude of moment arm and the magnitude of the force

Moment of Force = Moment Arm x Force By grasping the wrench at the end (A) a

greater torque is generated because the moment arm is greater than in (B)

Factors affecting the moment of force

A. Balanced teeter-totter

C. Increasing the applied force by adding a friend

B. Increasing the moment arm by leaning backwards

D D

Mass and Inertia Concepts

Mass is the measure of how much matter an object has

Inertia is the reluctance of an object to change its state of motion from rest to moving, to moving faster, or to slowing down back to rest

Moment of inertia is a function of the mass of a rotating object and how its mass is distributed about its axis of rotation

The mass distribution of an individual about the longitudinal axis (A) and about a horizontal axis (B)

Centre of Mass

• Located at the balance point of a body; a point found in or about a body where the mass could be concentrated

• Generally, 15 cm above the pubic symphasis, or approximately 55% of standing height in females and 57% in males

Centre of mass outside of body

Weight vs. Mass• Mass - a measure of inertia - measured in kilograms (kg)

• Weight - measure of the force of gravity (g) - measured in Newtons (N) - varies directly with the magnitude of the acceleration due to gravity

(9.8 m/s2)

W = m x g