Chapter2 - PHYS276 S09 Chapter 2 1 Chapter 2 Demos...

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Unformatted text preview: PHYS276, S09 Chapter 2 1 Chapter 2 Demos: http://www.physics.umd.edu/deptinfo/facilities/lecdem/lecdem.htm C2-07: free fall- equal time intervals (c2-06 in 0405) C2-10: constant velocity C4-33: free fall in vacuum – feather and ball A meter stick and a ball Crumbled paper and ball, dropped Thanks to Prof LaPorta and “Peer Instruction” by Eric Mazur HW PHYS276, S09 Chapter 2 2 Please remember that your first HW is due Monday. Please bring your HW to class on that day. Kinematics PHYS276, S09 Chapter 2 3 Our goal: predict the motions of inanimate objects (and occasionally animate ones). Will start simple and just predict the bulk motion. Then, we will look at more complex things like the motion within a body (spinning, stretching, etc). For now, will treat an object as a point. Will learn several different methods to make the same prediction. Some will be easier to use on one problem, some for another. Some will just give us a different kind of insight into what governs the motion of objects. This chapter • vocabulary for describing motion • motion of objects in free fall near the surface of the earth kinematics PHYS276, S09 Chapter 2 4 Typical questions we’ll be asking: • how far will it go? • how fast will it be going when it hits the ground? • How long will it take? • How hard do I have to push it? PHYS276, S09 Chapter 2 5 Chapter 2 • definitions of displacement, velocity, speed, and acceleration in 1-D • definition of “average” and “instantaneous” • graphing 1-D motions • 1-D motion with constant acceleration, especially freely falling bodies • for now, will be dealing with “point-like” objects. We will discuss “extended” objects later. Be careful! Physicists often take common words and redefine them! It is very important to memorize the exact definition of these terms, and not to be confused by the everyday usage! Motion PHYS276, S09 Chapter 2 6 What do we need to complete define a motion, so it can be exactly reproduced by anybody? • will learn several tools PHYS276, S09 Chapter 2 7 Position Need to define an origin and a measure. mks unit: meter m Be careful! For many questions, it is important to know where your ruler is! 1D ruler for 1D chapter Time: again, there is an implied ruler: the start time of some clock, that needs to be specified. t Example PHYS276, S09 Chapter 2 8 What was the position of this object for t=0s? t=0.5s? t=1s? Time (s) Position (m) PHYS276, S09 Chapter 2 9 Importance of Δ In physics, an objects location, speed, etc is often defined by “initial conditions”, which are not something that can be predicted. What can be predicted, instead, is changes. Δ : final - initial Δ ’s also don’t depend on the origin of the coordinate system Be careful! Physicists often use the same symbol to mean two different things! They often use two different symbols to mean the same thing! Different physicists use different symbols to mean the same thing! Learn *what* it is, not the symbol! PHYS276, S09...
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Chapter2 - PHYS276 S09 Chapter 2 1 Chapter 2 Demos...

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