EDU4SBM Sports Biomechanics 1 Lecture Week 6 Angular Motion, Torque, Mom of Inertia, Magnus Effect EDU4SBM Sports Biomechanics 2 Angular Motion Angular motion occurs when an athlete or object rotates about an axis of rotation The axis may be EDU4SBM Sports Biomechanics 3 Axes in the human body EDU4SBM Sports Biomechanics 4 Factors which affect angular motion Angular velocity Torque Moment of Inertia EDU4SBM Sports Biomechanics 5 Angular velocity EDU4SBM Sports Biomechanics 6 Torque Athletes produce the turning effect of torque any time they apply force at a distance from an axis. The size of the torque depends on the size of the force and the perpendicular distance from the axis of rotation to the line of the force. EDU4SBM Sports Biomechanics 7 Making Objects Rotate An increased torque results in an increase turning effect. ________________________ _________________________ EDU4SBM Sports Biomechanics 8 How athletes make themselves rotate Same principals as volleyball and tennis (See Figure 4.18 Carr) EDU4SBM Sports Biomechanics 9 Angular Momentum. Newtons First Law applied to Angular Motion A rotating body will continue to rotate about its axis of rotation with constant angular momentum, unless acted on by an external force. If angular momentum remains constant this means 1)If moment of inertia increases then angular velocity decreases 2) If moment of inertia decreases then angular velocity increases EDU4SBM Sports Biomechanics 10 Moment of Inertia Moment of Inertia is the angular counterpart to mass Moment of Inertia a bodies resistance to change in angular motion Moment of Inertia has two components: EDU4SBM Sports Biomechanics 11 Moment of Inertia and Angular Velocity in Diving Straight Dive MOI _________ AV ___________ Tuck Dive MOI _________ AV ___________ PikeDive MOI __________ AV ___________ EDU4SBM Sports Biomechanics 12 Angular Momentum in Figure Skating A good example of angular momentum in action is with figure skaters. A figure skater starts a spin by pulling in his arms to lessen his Moment of Inertia. By the Conservation of Momentum Principles, the angular speed must then increase. To come out of the spin, a skater simply extends her arms to increase angular momentum and decrease angular velocity. EDU4SBM Sports Biomechanics 13 Examples in Sport 1.Children gripping a baseball bat/ tennis racquet further up the handle. Why ?? 2.Running: Why do we flex out leg at the knee in the recovery phase in running? 3.Diving: Why is a front somersault performed in a tucked position easier than one performed in a piked position? EDU4SBM Sports Biomechanics 14 Types of Spin Spin is the rotation of a body or object. Torque is the force which creates spin. The type and amount of spin depends on how much torque is applied and where it is applied. EDU4SBM Sports Biomechanics 15 Magnus Effect When sports players produce curve balls, be it through throwing, kicking or hitting a ball, they are exploiting the Magnus Effect EDU4SBM Sports Biomechanics 16 Air around a rotating baseball, from balls top point of view Higher v, lower P on right Lower v, higher P on left So ball curves to right P left P right Boundary layer EDU4SBM Sports Biomechanics 17 Magnus Effect is a lifting force produced when a rotating cylinder produces a pressure differential. This is the same effect that makes a baseball curve or a golf ball slice. EDU4SBM Sports Biomechanics 18 Outcome of Spin Players learn to control the amount of spin to achieve different effects. Name 5 different sporting skills where it is an important aspect ? _________________________ EDU4SBM Sports Biomechanics 19 EDU4SBM Sports Biomechanics 20 Examples of curving balls Baseball curve pitch Baseball outfield throw with backspin for longer distance Tennis topspin to keep ball down Soccer (Beckham) curve around to goal Golf balls (Johns occasional duck hook)