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Angular Motion - PHYSICS 215 ANGULAR MOTION Object The...

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1 PHYSICS 215 ANGULAR MOTION Object: The object of this experiment is to measure some properties of rotating systems and to demonstrate how Newton’s 2 nd Law applies to rotating systems. Apparatus: Rotary Motion Sensor disk ring 50-g weight holder triple beam balance vernier caliper thread 1. Introduction In the study of linear motion, objects were treated as point particles without structure; it did not matter where a force was applied, only whether it was applied or not. The reality is that the point of application of force does matter. In tennis, for example, if a tennis ball is struck with a strong horizontal force acting through its center of mass, it may travel a long distance before hitting the ground, far out of bounds. Instead, the same force applied in an upward, glancing stoke will yield topspin to the ball, which can cause it to land in the opponent’s court. The concepts of rotational equilibrium and of rotational dynamics are also important in other disciplines. For example, students of architecture benefit from understanding the forces that act on buildings, and biology students should understand the forces at work in muscles, bones, and joints. These forces create torques, which tell us how the forces affect an objects equilibrium and rate of rotation. We will find that an object remains in a state of uniform rotational motion unless acted on by a net torque. This principle is the equivalent to Newton’s first law. Further the angular acceleration of an object is proportional to the net torque acting on it, which is the analog of Newton’s Second Law. A net torque acting on an object causes a change in its rotational energy. Finally, torques applied to an object through a given time interval can change the objects angular momentum. In the absence of external torques, angular momentum is conserved, a property that explains some of the mysterious and formidable properties of pulsars—remnants of supernova explosions that rotate at equatorial speeds approaching that of light. 2. Theory 2.1 Translation and Rotation A rigid body is defined as an object in which the relative separations of the component particles are unchanged, the displacement of any one particle with respect to any other particle in the body being fixed. No truly rigid body exists: external forces can deform any solid. For our purposes, then, a rigid body is a solid in which the internal forces between the fundamental particles changes so drastically with a variation in their relative separation that large forces are required to deform it. Up to this point, we have studied the kinematics and dynamics of a particle whose position in three-dimensional space is completely specified by three coordinates. To describe a change in the position of a body of finite extent, such as a rigid body, is much more complicated. For convenience, it is regarded as a combination of two distinct types of motion: translational motion and rotational motion.
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