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Unformatted text preview: Physics 1C Lecture 12A "We learn and grow and are transformed not so much by what we do but by why and how we do it." Sharon Salzberg Information Problem solving sessions will be: Thursday 8:00pm9:50pm starting this week @ Solis 104 First day we will use clickers will be Friday Facebook page UCSD Phys 1C Questions, answers, comments Post notes, quiz example questions Solis York Outline Today we discuss ideas of Simple Harmonic Motion (SHM) Results from force that drive to restore system to equilibrium Physical examples used today Think of biological examples Mass on a Spring Lets say we have a mass hanging from a spring. What would a force diagram look like for the mass in this situation? mass F gravity, Earth on mass F pull, spring on mass F y = 0 a y = 0 The spring pulls up on the mass so that it does not accelerate. Mass on a Spring But what would happen if we added another mass to the bottom of the system? The spring stretches further, but ultimately comes to rest. We have added more force of gravity and the spring added more force by displacing it more from its equilibrium position. Also, what if we had used another spring, would the extra displacement be the same? Not necessarily, it depends on the type of spring used. Mass on a Spring This pull force from the spring (also known as a restoring force, F spring ) will resist either a compression or a stretching. In general, each spring will have a different resistance to a certain displacement. Hookes Law gives the value of restoring force as a function of displacement: where k is a constant of proportionality also known as the spring constant (units of k are [N/m]). Mass on a Spring The minus sign in Hookes Law is to show that the restoring force is opposite in direction to the displacement vector....
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 Fall '07
 Smith
 Physics

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