PHY 102 1nd Edition Lecture 12 Outline of Last Lecture I First Law of Motion summary II Second Law of Motion III Blue Book Outline of Current Lecture I Summary of Dynamics 1st and 2nd laws II Third Law III Work and Energy IV Work and Kinetic Energy V Work done by Gravity Potential Energy VI Conservation of Mechanical Energy VII Blue Book Problems Current Lecture I II III Summary of Dynamics 1st and 2nd laws a First Law i p mv ii Momentum does not change b Second Law i Fnet ma ii F and a are in the same direction Third Law a FAB FBA i Two objects A B b If A acts on B then B acts on A ALWAYS with an equal force in the opposite direction c EXAMPLE If you are pushing a table with a force of 10 N and it does not move the table is pushing back on you with a force of 10 N If you are pushing a table with a force of 15 N and it moves the table is still pushing back on you with a force of 15 N Work and Energy a Relation between work force and displacement i Positive work helping motion ii Negative work retarding motion These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute IV V VI VII iii W 0 nothing is happening b W FIId i Both F and d must be nonzero ii F must have a component parallel to d iii W can be positive or negative iv Unit for work N m Joules J Work and Kinetic Energy a As force does work on a system it changes the system s speed b The change in speed is related to a change in kinetic energy KE c Recall Q Qf Qi d W KE e KE mv2 f Wgravity mg h1 h2 mgh1 mgh2 g KE KE2 KE1 h mgh1 KE1 mgh2 KE2 Work done by Gravity Potential Energy a PE mgh b What is h i It is the height above some arbitrary reference level Conservation of Mechanical Energy a PE1 KE1 PE2 KE2 b Total mechanical energy does not change c ME KE PE i ME is constant does not change Blue Book Problems
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