Wind Turbines 1 Wind Turbines 2 Introductory Question Introductory Question You and a child half your height lean out over You and a child half your height lean out over � the edge of a pool at the same angle. If you the edge of a pool at the same angle. If you Wind Turbines Wind Turbines both let go simultaneously, who will tip over both let go simultaneously, who will tip over faster and hit the water first? faster and hit the water first? faster and hit the water first? faster and hit the water first? You You A. A. The small child The small child B. B. Wind Turbines 3 Wind Turbines 4 Observations about Observations about 6 Questions about Wind Turbines 6 Questions about Wind Turbines Wind Turbines Wind Turbines � Wind turbines are symmetrical and balanced Wind turbines are symmetrical and balanced � How does a balanced wind turbine move? How does a balanced wind turbine move? � A balanced wind turbine rotates smoothly A balanced wind turbine rotates smoothly � Why does the wind turbine need a pivot? Why does the wind turbine need a pivot? � An unbalanced turbine settles heavy An unbalanced turbine settles heavy- -side down side down � Why does a one Why does a one- -blade turbine spin unevenly? blade turbine spin unevenly? � Most wind turbines have three blades Most wind turbines have three blades � Why do blade weights and orientations matter? Why do blade weights and orientations matter? � Wind turbines start or stop spinning gradually Wind turbines start or stop spinning gradually � Why do giant turbines start and stop so slowly? Why do giant turbines start and stop so slowly? � Wind turbines extract energy from the wind Wind turbines extract energy from the wind � How does energy go from wind to generator? How does energy go from wind to generator? and convert it into electrical energy and convert it into electrical energy Wind Turbines 5 Wind Turbines 6 Question 1 Question 1 Physics Concept Physics Concept � How does a balanced wind turbine move? How does a balanced wind turbine move? � Rotational Inertia Rotational Inertia � � Is a balanced wind turbine horizontal? Is a balanced wind turbine horizontal? � A body at rest tends to remain at rest A body at rest tends to remain at rest � Is a horizontal wind turbine balanced? Is a horizontal wind turbine balanced? � A body that’s rotating tends to keep rotating A body that’s rotating tends to keep rotating 1
Wind Turbines 7 Wind Turbines 8 Newton’s First Law Newton’s First Law Physical Quantities Physical Quantities of Rotational Motion of Rotational Motion � Angular Position Angular Position � A rigid object that’s not wobbling and that is A rigid object that’s not wobbling and that is – an object’s orientation an object’s orientation free of outside torques rotates at a constant free of outside torques rotates at a constant angular velocity. angular velocity. � Angular Velocity Angular Velocity – change in angular position with time change in angular position with time change in ang lar position with time change in ang lar position with time � Torque Torque – – a twist or spin a twist or spin Wind Turbines 9 Wind Turbines 10 Balanced Wind Turbine Balanced Wind Turbine Question 2 Question 2 � All by itself, a balanced wind turbine All by itself, a balanced wind turbine � Why does the wind turbine need a pivot? Why does the wind turbine need a pivot? � experiences zero net torque experiences zero net torque � How would a How would a pivotless pivotless wind turbine move? wind turbine move? � has a constant angular velocity has a constant angular velocity � Its angular velocity is constant when it is I Its angular velocity is constant when it is I l l l l i i i i h h i i i i � motionless and horizontal motionless and horizontal � motionless and tilted motionless and tilted � turning steadily in any direction turning steadily in any direction Wind Turbines 11 Wind Turbines 12 Center of Mass Center of Mass Wind Turbine’s Pivot Wind Turbine’s Pivot � The point about which an object naturally spins The point about which an object naturally spins � The wind turbine needs a pivot to The wind turbine needs a pivot to � A free object rotates about its center of mass A free object rotates about its center of mass � support the weight of the turbine support the weight of the turbine while its center of mass follows the path of a while its center of mass follows the path of a � prevent the turbine from falling prevent the turbine from falling falling object falling object falling object falling object � p rmit th t rbin t r t t b t n t tr n l t � permit the turbine to rotate but not translate p rmit th t rbin t r t t b t n t tr n l t permit the turbine to rotate but not translate � Placing the pivot at turbine’s center of mass Placing the pivot at turbine’s center of mass � allows the turbine to spin about its natural pivot allows the turbine to spin about its natural pivot � minimizes the forces required of the pivot minimizes the forces required of the pivot 2
Wind Turbines 13 Wind Turbines 14 Question 3 Question 3 Physical Quantities Physical Quantities � Why does a one Why does a one- -blade turbine spin unevenly? blade turbine spin unevenly? � Angular Position Angular Position – an object’s orientation an object’s orientation � How does a torque affect a wind turbine? How does a torque affect a wind turbine? � How does gravity exert a torque on the turbine? How does gravity exert a torque on the turbine? � Angular Velocity Angular Velocity – change in angular position with time change in ang lar position with time change in ang lar position with time change in angular position with time � Torque Torque – – a twist or spin a twist or spin � Angular Acceleration Angular Acceleration – change in angular velocity with time change in angular velocity with time � Rotational Mass Rotational Mass – – measure of rotational inertia measure of rotational inertia Wind Turbines 15 Newton’s Second Law Wind Turbines 16 Newton’s Second Law Forces and Torques Forces and Torques of Rotational Motion of Rotational Motion � An object’s angular acceleration is equal to the An object’s angular acceleration is equal to the � A force can produce a torque A force can produce a torque net torque exerted on it divided by its rotational net torque exerted on it divided by its rotational � A torque can produce a force A torque can produce a force mass. The angular acceleration is in the same mass. The angular acceleration is in the same direction as the torque. direction as the torque direction as the torque. direction as the torque torque = lever arm · force torque = lever arm · force (where the lever arm is perpendicular to the force) (where the lever arm is perpendicular to the force) angular acceleration = net torque/rotational mass angular acceleration = net torque/rotational mass net torque = rotational mass · angular acceleration net torque = rotational mass · angular acceleration Wind Turbines 17 Wind Turbines 18 Clicker Question Clicker Question Clicker Question Clicker Question � To make Mini To make Mini- -Me undergo clockwise angular Me undergo clockwise angular � When a student strikes the right side of this When a student strikes the right side of this acceleration, I should knock acceleration, I should knock balanced bar with a mallet, the bar will undergo balanced bar with a mallet, the bar will undergo tremendous clockwise angular acceleration. The tremendous clockwise angular acceleration. The egg will break egg will break egg will break egg will break � the top of his head toward his feet. the top of his head toward his feet. h h f hi h f hi h d d d hi f d hi f � the side of his head toward your right. the side of his head toward your right. � while it is accelerating upward on the bar. while it is accelerating upward on the bar. � the middle of his body toward your right. the middle of his body toward your right. � when it hits the ground after its flight. when it hits the ground after its flight. � the side of his feet toward your right. the side of his feet toward your right. � in midair. in midair. 3
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