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Unformatted text preview: 1 Chapter 2 Motion along a Straight Line Terms we will use: • Position, distance, displacement • Speed, velocity (average and instantaneous) • Acceleration (average and instantaneous) Coordinate Systems A coordinate system is used to describe location. A coordinate system consists of: • a fixed reference point called the origin • a set of axes • a definition of the coordinate variables Example The position of an object is its location in a coordinate system. x y (4,2) cartesian The arrow indicates the “positive” direction. (3,5) Today we’ll deal only with onedimension, and usually call it x x (0,0) (0,0) = “the origin” Distance and Displacement Displacement is defined as the change in position of an object. • It can be positive, negative or zero. • Displacement is a vector . Distance is the total length of travel. • It is always positive. • It is measured by the odometer in your car, for example. x x 1 x 2 2 Average Speed and Velocity Speed and velocity are not the same in physics! SI units of speed and velocity are m/s. (always positive, or zero) (positive, negative or zero) velocity is a vector x x 1 x 2 Example What is the average speed of a person at the equator due to the Earth’s rotation? What is the average velocity of a person at the equator due to the Earth’s rotation? The Dragster Physlet I2.1 ; I2.2 Graph of the Position of the Dragster as a Function of Time 3 Position vs. Time Plots The average velocity between two times is the slope of the straight line connecting those two points. average velocity is positive average velocity is negative Instantaneous Velocity The velocity at one instant in time is known as the instantaneous velocity and is found by taking the average velocity for smaller and smaller time intervals: (e.g. the speedometer indicates the magnitude of instantaneous velocity) x t in the limit this gives the tangent to the curve Velocity as a Slope of Tangent Line on a Graph of x vs. t On a graph of position as a function of time, the slope of the tangent line at any point is the velocity at that point....
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 Spring '08
 Sukenik
 Physics, Acceleration, Velocity, race car

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