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Biomechanics

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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

- Focuses on the various forces that are associated with a movement

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

General motion

Angular motion

Types of Motion

Linear 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 motionoccurs when movement follows a straight line
- Curvilinear motionoccurs 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 rotationis 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
- Forceis any action, a push or pull, which tends to cause an object to change its state of motion by experiencing an acceleration
- Constant Velocityoccurs when an object is not accelerating
- Linear Motionis caused by forces which act through a body’s centre of mass
- Angular motionis 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

head

tail

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)

- vectors are straight-line segments with one end defined

as the tail and the arrow tip defined as the head.

a

a

b

b

Resultant

Resultant

+

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

=

Calculating net external force using free body diagrams

Levers

- Simple machines that augment the amount of work done by an applied force
- Axis/Fulcrum (A) - A rigid body (i.e., long bone) that rotates about a fixed point (i.e., joint)
- Load (L) – Weight acting on the lever (i.e. weight of a limb segment)
- 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)

D

D

Factors affecting the moment of force

A. Balanced teeter-totter

B. Increasing the moment arm by leaning backwards

C. Increasing the applied force by adding a friend

Mass and Inertia Concepts

- Massis 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

outside of body

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

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