PHY 102 1nd Edition Lecture 12 Outline of Last Lecture I. First Law of Motion (summary)II. Second Law of MotionIII. Blue BookOutline of Current Lecture I. Summary of Dynamics (1st and 2nd laws)II. Third LawIII. Work and EnergyIV. Work and Kinetic EnergyV. Work done by Gravity: Potential EnergyVI. Conservation of Mechanical EnergyVII. Blue Book ProblemsCurrent LectureI. Summary of Dynamics (1st and 2nd laws)a. First Lawi. p = mvii. Momentum does not changeb. Second Lawi. Fnet = maii. F and a are in the same directionII. Third Lawa. FAB = -FBAi. Two objects A & Bb. If A acts on B, then B acts on A ALWAYS with an equal force in the opposite directionc. 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.III. Work and Energya. Relation between work, force, and displacementi. Positive work = helping motionii. Negative work = retarding motionThese 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.iii. W = 0 (nothing is happening)b. W = FIIdi. Both F and d must be nonzeroii. F must have a component parallel to diii. W can be positive or negativeiv. Unit for work = N*m = Joules (J)IV. Work and Kinetic Energya. As force does work on a system, it changes the system’s speedb. The change in speed is related to a change in kinetic energy (KE)c. Recall: ∆Q = Qf - Qid. W = ∆KEe. KE = ½ mv2f. Wgravity = mg(h1 – h2)= mgh1 – mgh2g. ∆KE = KE2 – KE1h. mgh1 + KE1 = mgh2 + KE2V. Work done by Gravity: Potential Energya. PE = mghb. What is h?i. It is the height above some arbitrary reference levelVI. Conservation of Mechanical Energya. PE1 + KE1 = PE2 + KE2b. Total mechanical energy does not change!c. ME = KE + PEi. ME is constant (does not change)VII. Blue Book
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