# l12 - Today Announcements HW and Extra credit#3 due 2/25 HW...

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ISP209s10 Lecture 12 -1- Today • Announcements: – HW and Extra credit #3 due 2/25 • HW hints + Recap the 2nd law of thermodynamics • Electric and Magnetic Forces and their unification • the Force Field concept

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-2- HW #5 Hints 1) The speed at D is …… than the speed at A 2) The speed at D is …… than the speed at C 3) The acceleration at D is zero, true or false 4) The acceleration at A points in the ……. Direction a) +x b) - x c) +y d) -y e) none, it is zero Hint: Questions 1,2 use Conservation of energy Hint: think of circular Motion for ?’s 3,4
ISP209s10 Lecture 12 -3- HW #5 Hints 1) The speed at D is …… than the speed at A Conservation of energy E A = E B = E C = E D At initial point B, ALL energy is potential energy E B = mgh B At point A, we have a mix of PE and KE E A = mgh A + 1/2 mv A 2 At point D, we have a mix of PE and KE E D = mgh D + 1/2mv D 2

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ISP209s10 Lecture 12 -4- HW #5 Hints 1) The speed at D is …… than the speed at A Conservation of energy E A = E B = E C = E D A D Speed at A is > speed at D (common sense!)
ISP209s10 Lecture 12 -5- HW #5 Hints Think of circular motion to answer Questions about Acceleration at A and D Let’s illustrate this with a familiar example -- the moon Orbiting the earth in a circular orbit.

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ISP209s10 Lecture 12 -6- HW # 5 Hints Is the moon experiencing Acceleration? YES, since The direction of velocity Is changing at each point. What direction is the Acceleration? It is in The same direction as the Force that is causing it (I.e., towards the center Of the circlular orbit).
ISP209s10 Lecture 12 -7- HW #5 Hints Think of circular motion to answer Questions about Acceleration at A and D At these points, the wire forms a small segment of A circular path. We learned that in circular motion, An object is being accelerated, and the direction of Acceleration is towards the center of the circle.

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Energy and Entropy - Pendulum Example Energy If there is no friction, the pendulum swings forever, always following the same trajectory. The figure shows how the energy is split into Kinetic And Potential energy at each point in the trajectory.
ISP209s10 Lecture 12 -9- Energy and Entropy - Pendulum Example Energy The thermal energy (heat) is “lost”

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ISP209s10 Lecture 12 -10- Entropy • Entropy is a measure of the number of ways a system can be arranged. S = k B ln(# of arrangements) • S = Heat/T – thermal energy goes toward increasing the entropy • Second Law of Thermodynamics – The entropy of a closed system always increases.
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l12 - Today Announcements HW and Extra credit#3 due 2/25 HW...

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