PHY 102 1st Edition Outline of Last Lecture I Examples of Newton s Second Law a Car acceleration b Collision Example c Weight d Change in Velocity II Experience and Experiment a Experience shows that b Experiment Shows that III Newton s Third Law Outline of Current Lecture I Work a Definitions b Equations c Young s Experiment II Motion III Mechanical Energy a Kinetic energy b Elastic equations IV Power 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 V VI Conservation of Energy Frictional Force Current Lecture I Work a Work is done only when energy is expended b Physical work is not the same as physiological work i Physical work occurs when there is motion involved c Work is defined as force x distance f d d Work causes a change in the energy of a body f d E e Impulse causes a change in momentum f Equations i We mg ii W mg h or W mg x iii F d usually used for horizontal problems g Young i Tried to measure how much work it takes to dig a hole and a hole 2x the size ii A ball was dropped in a bowl of meat fat from different heights to measure the length of the whole formed in the fat 1 Work is proportional to v2 2 Work is proportional to mass 3 Work is proportional mv2 II Motion a mv2 so energy can be conserved b Work energy theorem F d E c Impulse momentum principle F t m v III Mechanical Energy a Kinetic energy mv2 b Gravitational potential energy mgh i Hooke s law F k x and PEg k x 2 c Elastic potential energy kx2 i K spring constant with units F x d The unit of work or energy is the Nm or Joule e Like momentum mechanical energy is always conserved but not in a way that we can easily account for all of the energy f Energy is meaningfully conserved only in isolated systems and perfectly elastic collisions i Produce sound light heat deform objects ii Most collisions are inelastic iii elastic collision would be two steel balls 1 all energy goes in all energy comes out easily measured IV Power a Power is the rate at which energy is produced or consumed b P energy transferred unit time E t c Unit of power Nm s J s Wat V Conservation of Energy a An object falls after being released from rest b An amusement park cart collides with a spring c A moving roller coaster reaches botom i V1 v0 at ii Vf2 2a x 2a x iii Vf d On a slope the acceleration is not 9 81 m s2 VI Under frictional force a Work F d E work energy principle b A block slides under frictional force M Vi W E E1 1 mv 2 E E 2 i f Ei 0 mvi2 W F x f x 0 1 2mv2 f x mvi2
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