Physics Study Guide 2
Physics Study Guide 2 Physics 125
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This 5 page Study Guide was uploaded by Nora Salmon on Sunday March 8, 2015. The Study Guide belongs to Physics 125 at University of Alabama - Tuscaloosa taught by Prof. Andreas Piepke in Fall2015. Since its upload, it has received 264 views. For similar materials see Physics 1 w/Calculus in Physics 2 at University of Alabama - Tuscaloosa.
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Date Created: 03/08/15
Energy What is it 9Energy is a universal currency It can be neither created nor destroyed 9Energy is a scalar quantity 9Types we focus on Mechanical energy gravitational energy Work What is work 9It is the energy transferred to or from an object 9It is a scalar quantity 9 The product of a force and the displacement acting parallel or antiparallel to the force vector Work with a constant force W F d cos I 9Sometimes the force acting over some distance is constant We can simply multiply the two together Other times a variable force acts and we must graph force as a function of distance and integrate the graph to find the work done What happens when several forces are acting on an object 9Net work W Fnetd cos I WorkKinetic Energy Theorem Energy in terms of work 9 energy is the ability to perform work 9 Energy stored in motion is called kinetic energy 9 Kinetic energy is dependent on the mass and final and initial velocities of an object Change in kinetic energy K mvfz mviz 9When a net force on an object does work and the only change in the object is its speed the work done equals the change in the object s kinetic energy Potential Energy 9Potential energy is associated with an object s position or environment 92 cases in this class energy stored in an object being lifted energy stored in a compressed spring 9A spring force is a type of variable force Hooke s Law for a spring force F K 55 Work done by a spring W 106 Gravitational Potential Energy 9 Depends on the height of an object over a constant reference level Gravitational Potential Energy PE 2 mgh Conservative and NonConservative Forces 9Conservative force work done does not depend on the path taken 9Examples gravitational force elastic force depends on initial and final positions like difference in elevation or length change 9Nonconservative force work done depends on the chosen path 9Example frictional force longer path requires more work coefficient of friction may be different for different surfaces 9What is the relationship between non or conservative forces and PE 9PE can only be defined for a conservative force 9A force is conservative only if the total energy transferred to from an object on a closed path 0 net distance O and net work 0 What does this mean For conservative forces mechanical energy is conserved 9Conservation of mechanical energy K E i PE i K E f PEf Conservation of Energy 91f a system is isolated the change in energy of the system O 9Work Energy Transfer 0 9Then AKE APE W ET 2 0 ln an open system where nonconservative forces act 9AKE APE 2 Wm Power 9Power is the amount of work done energy transferred per unit time 9Unit Watt Is dW 9Power in terms of force P E Fpamllel v w 9Linear momentum p the product of an object s mass and its velocity 9Momentum 15 m1gt 91f no external forces are acting on a system of objects while the objects collide momentum is conserved 9How do we define a change in momentum lt s called impulse a change in momentum as a function of time 91mpulse I 2 A13 2 fig 13quot dt this is called an integral of motion Momentum and Net Force 9The net force acting on an object is the time derivative of the object s d1 momentum Fnet E Momentum and Kinetic Energy 9KE and momentum are both related to an object s motion we can therefore relate them to one another 2 9KE in terms of momentum p K E 2 n m 9There are three types of collisions elastic inelastic and totally inelastic Types of Collisions Momentum KE Conserved Conserved Elastic Two particles Yes Yes collide and bounce off one another Inelastic Two particles Yes No some is lost to collide and heat experience some deformation Totally inelastic Two particles Yes No some is lost to collide and stick heat or deformation together after the collision Center of Mass 9What is an object s center of mass 9The object moves as though the system s mass is all concentrated there and all external forces acting on the system are applied there 9For a twoparticle system the center of mass xcom m2 m1m2 9More than two particles 9We can expand the com equation to include many particles 9 m1x1m2x2mnxn xcom M 9Can we define center of mass in multiple dimensions 9Yesfor threedimensional objects the com must be identified by three coordinates 9X i f x dm M 9Yi f y dm 9Zi f 2 dm M gt 9W1tl 1 Tcm xcmyycmrzcm COM and Linear Momentum 91f a bunch of particles or objects acts as a system we can relate its com and momentum a 9Linear momentum of a system P M 13mm Rotational Motion 9We can describe the motion of rigid bodies that rotate around a fixed axis a rotation axisquot 9Angular position description of location along the circumference of the rotational path 9 9 is arc length fraction of the circumference 9Always measure the angle in radians 9Angular velocity the change in angular position over a period of time 9Angular velocity u limAH0 2 9Angular acceleration is the time derivative of the angular velocity Aw 9Angular acceleratlon a l1mAt0 A t 91f an object experiences angular acceleration then it experiences radial AND tangential acceleration 9Tangential acceleration at 11quot 2 9Radial acceleration a1 2 v7 wzr 9Rotational motion follows Newton s 2rld lawbut what makes an object rotate 9Torque the tendency of a force to make an object rotate about some axis 9Torque T rsin F 9Torque is a vector so torques are additive 9Even if there is no net force there may be a net torque Rotational Motion and Kinematic Equations 9We can use a set of equations much like the equations for the kinematic equations for linear displacement to describe rotational motion 9What s the difference Angular velocity replaces linear velocity angular acceleration replaces linear acceleration and angular displacement replaces linear displacement Torque Inertia and Netwon s 2nd Law 9Rotational inertia tells us how the mass of the rotating body is distributed about its axis of rotation 9Rotational Inertia I Z miriz 9TorqueFtangtIltrmamnrmr2aIa2miri2 a Rotational Kinetic Energy 9Rotational kinetic energy does not 0 9Rotational kinetic energy I Z miriz
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