PHY 102 1st EditionOutline of Last LectureI. Examples of Newton’s Second Lawa. Car accelerationb. Collision Examplec. Weightd. Change in VelocityII. Experience and Experimenta. Experience shows that:b. Experiment Shows that:III. Newton’s Third LawOutline of Current Lecture I. Worka. Definitionsb. Equationsc. Young’s ExperimentII. MotionIII. Mechanical Energya. Kinetic energyb. Elastic equationsIV. PowerThese 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. Conservation of EnergyVI. Frictional ForceCurrent LectureI. Worka. Work is done only when energy is expendedb. Physical work is not the same as physiological worki. Physical work occurs when there is motion involvedc. Work is defined as force x distance; f∆dd. Work causes a change in the energy of a body: -f∆ d =∆ Ee. Impulse causes a change in momentumf. Equationsi. We = mgii. W = mg∆ hor W = mg∆ xiii. F∆ d usually used for horizontal problemsg. Youngi. Tried to measure how much work it takes to dig a hole and a hole 2x the sizeii. 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 v22. Work is proportional to mass3. Work is proportional mv2II. Motiona. ½ mv2 so energy can be conservedb. Work energy theorem (-F∆ d =∆ E)c. Impulse-momentum principle (-F∆ t =m ∆ v ¿III. Mechanical Energya. Kinetic energy = ½ mv2b. Gravitational potential energy = mghi. Hooke’s law: F=k∆x and PEg = ½ k∆ x2c. Elastic potential energy = ½ kx2i. K = spring constant with units F/∆ xd. The unit of work or energy is the Nm or Joulee. Like momentum, mechanical energy is always conserved but not in a way that wecan easily account for all of the energyf. Energy is “meaningfully” conserved only in “isolated” systems and perfectly elastic collisionsi. Produce sound, light, heat, deform objectsii. Most collisions are inelasticiii. elastic collision would be two steel balls1. all energy goes in – all energy comes out easily measuredIV. Powera. Power is the rate at which energy is produced or consumedb. P = energy transferred/unit time = E/tc. Unit of power, Nm/s = J/s = WatV. Conservation of Energya. An object falls after being released from restb. An amusement park cart collides with a springc. A moving roller coaster reaches botomi. V1 = v0 + atii. Vf2 = 2a∆xiii. Vf = √2a ∆ xd. On a slope the acceleration is not 9.81 m/s2VI. Under frictional force…a. Work F∆ d=∆ E (work-energy principle)b. A block slides under frictional forceViW = ∆ EE1= 12mvi2∆ E=Ef - Ei= 0 – ½ mvi2W = F∆ x-f∆ x=¿ 0-1/2mv2f∆ x=¿ ½
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