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# l12p - Today Announcements HW#5 is due by 8:00 am tomorrow...

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ISP209s8 Lecture 12 -1- Today • Announcements: – HW#5 is due by 8:00 am tomorrow, Wednesday February 20th. HW#6 is due next week. – The third extra credit problem is due tomorrow at 8:00am • Entropy and the Second Law of Thermodynamics • Electric and Magnetic Forces ISP209s8 Lecture 12 -2- Energy and Entropy - Pendulum Example Energy The thermal energy (heat) is “lost” ISP209s8 Lecture 12 -3- Entropy • Entropy is a measure of the number of ways a system can be arranged. • S = Heat/T – thermal energy goes toward increasing the entropy • Second Law of Thermodynamics – The entropy of a closed system always increases. • As the pendulum swings useful energy is lost to increasing the random motion of the air and pivot • If this is true, we can’t go back in time. There is no way to recollect the thermal energy and make the pendulum swing higher (that is with a closed system). ISP209s8 Lecture 12 -4- Why? Why does the entropy of a system always have to increase? For now, lets say because that’s the way it seems to work. It probably has to do with how the Universe was formed, but that discussion is for later in the term.

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ISP209s8 Lecture 12 -5- A new force – Magnetic force Certain objects in nature have magnetic poles. They always come in pairs, north and south. Like poles repel Unlike poles attract Near the pole, the strength of the force decreases with the square of the distance. 2
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l12p - Today Announcements HW#5 is due by 8:00 am tomorrow...

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