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Unformatted text preview: Lecture 6 Mass-spring oscillation (Simple Harmonic Motion) 1 Review from Last Time Gravitational Force- Review depends on product of masses and one over distance squared (DRAW) direction of force - always attractive along line connecting objects vector F g = G m 1 m 2 r 2 r where r = | vector r 2- vector r 1 | is the distance between the two objects, and r is the unit vector pointing along the line connecting the two objects. also compare with electric force which can be attractive or repulsive Go over again how we see Newtons third law in this law. Distinguish between concept of forces versus acceleration. Conservation of Momentum There is another very important consequence of the Third Law: the total momentum of a system stays constant if no external forces act on the system. In other words, the total momentum does not change because of any mutual inter- actions between two objets. This is the law of Conservation of Momentum: If there is any kind of force, no matter how complicated, between two particles, and we measure or calculate the total momentum both before and after the forces act, the results should be equal. The total momentum does not change. 1D EXAMPLE: two massive particles start at rest. Is there a force on particle A? yes. Does its momentum change? Yes! But, it is compensated for by change in momentum of particle B such that the total momentum remains zero. Calculate v for each... PUZZLERS On the choice of system: * We can extend this to larger systems with three or more interacting particles....
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