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Biomechanics: Outline • Definition • Types of Motion • Measuring Motion • Describing the Geometry of Motion: Kinematics • Linear • Angular • Describing the Forces of Motion: Kinetics • Linear • Angular • Fluid Mechanics
Biomechanics • The study of the structure and functions of biological systems by means of the methods of mechanics Hatze, 1974
Motion • Kinematics • Kinetics
Types of motion • Linear (translation) • all parts travel the same distance in the same time along the same path
Type of Motion • Angular motion
General Motion Most movements are likely a combination of both linear and angular motion
Kinematics Kinetics Other Measuring Motion
Kinematics: Film Analysis SETUP CALIBRATION ANALYSIS
What might we measure? KINEMATICS: Spatial component • Position • Displacement • Distance
What might we measure? • Center of gravity the point about which a body’s weight is equally balanced in all directions (Hall, 1995)
Kinematics: Film Analysis CALIBRATION SETUP ANALYSIS (50,490) ( (10, 570)
What might we measure? Kinematics: Spatial and temporal components • Speed • Velocity • Acceleration
What might we measure? Kinetics • Inertia • Force
Motion, Force, and Sir Issac • First Law (Inertia)
Motion, Force, and Sir Issac • Second Law (Acceleration or F=ma) e.g.1, a soccer ball (of fixed mass) will experience greater acceleration when kicked with more force e.g.2, for kick (of given force) a lighter soccer ball will experience greater acceleration
Motion, Force, and Sir Issac • Third Law (action-reaction)
Angular Motion • When a force is not exerted along a line that passes through a body’s center of gravity ____________ the body will experience angular _________ motion
What might we measure? • Angular displacement • Angular distance angular motion consider in degrees, revolutions, or radians 1 radian = 57.3 degrees 1 revolution = 360 degrees 1 revolution = 6.28 radians
What might we measure? • Angular Velocity • Units? • Angular Acceleration • Units?
What might we measure? Angular Kinetics • Torque • Moment of inertia
Moment of Interia: Relative • Tuck • Pike • Full body rotating around center of mass • Full body rotating around a bar
Extended swing • around bar • Extended swing • around central axis • Pike • Tuck Assuming: Σmd2 Where: M = mass d = distance from axis of rotation
Fluid Mechanics • Drag • Lift
Drag Fluid force that opposes ________________________________________________________________________________________________ Will depend on:
Forms of Drag • Surface (hydrodynamic drag) • Profile (Form) • Wave
Surface Drag Water particles attract other water particles and will increase with “roughness of skin”
Profile Drag • Low pressure pocket forms • and “holds back” the • cyclist. As velocity doubles this • resistive force quadruples!!!! • Important factors:
Reducing Drag • Frame designs • on bikes are often • “tear-shaped” to • reduce drag • Drafting within 1 m • can reduce drag • accounting for 6% of • energy cost (e.g., ducks flying)
Lift Component of air resistance that ____________________________________________________________________ Lift Resultant Drag Air Flow
High velocity/Low Pressure Low velocity/High Pressure Lift - common example How might you use this principle in Formula 1 racing?
Intended Direction Flight Path Air Flow Low Pressure Magnus Effect • Force first discovered by Magnus. It explains the curving of a spinning ball. As the spinning object pushes the air from one side to the other, it will create a lower pressure zone, making the object move faster on one side.
Kinematics linear motion displacement, velocity.. Angular Motion angular displacement… Kinetics linear motion mass, inertia Angular Motion torque, moment of inertia Review • Fluid dynamics • drag • lift