文档介绍：Torque ? centric force – applied through axis (center) of rotation – creates no torque so causes no rotation ? eccentric force – applied some distance away from axis of rotation – creates torque so causes rotation Which door is easier to open? Will the green person go up or down? What causes a limb to rotate - force or torque? ? angular motion occurs at a joint, so torque causes the limb to rotate ? torque is developed because a force acts at a distance from the axis of rotation muscle force (F m) Perpendicular distance between pt of application and joint axis (d m) muscle torque (T m =F m*d m) Calculation of Muscle Torque 400 N NOTE: The torque created by the muscle depends on 1) the size of the muscle force 2) the angle at which the muscle pulls 3) the perpendicular distance from the muscle to the joint axis Example F m = ? W fa = N W bb = N m m m Give me a lever long enough and a fulcrum strong enough, and, single-handedly, I can move the world. --Archimedes (287 - 212 .) Levers ? A lever consists of two forces ( motive and resistance forces ) acting around a pivot point ( axis or fulcrum ).? The perpendicular distance from the line of action of the effort force to the fulcrum is called the motive arm .? The perpendicular distance from the line of action of the resistance force to the fulcrum is called the resistance arm . Elements of a Lever motive force (effort force) axis (fulcrum) motive arm resistance arm resistance force Mechanical Advantage of a Lever ? MA = ? The ratio of the motive arm to the resistance arm is called the mechanical advantage (MA). ? If MA is approximately 1 the lever simply acts to redirect the applied force. ? If MA is > 1 the lever acts to amplify the force. ? If MA is < 1 the lever acts to amplify the speed and range of motion. arm resistance arm motive MA = 1 motive force direction of the force vector is redirected motive arm = resistance arm