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Unformatted text preview: Change: motion Two questions: How do we describe motion? We want to analyze the motion mathematically The mathematical description of motion is called kinematics. How do we explain motion? The explanation of motion in terms of its causes is called dynamics. Newton's Law Concepts of Motion 1.1 Motion Diagrams 1.2 The Particle Model 1.3 Position and Time 1.4 Velocity 1.5 Acceleration 1.6 Examples of Motion Diagrams 1.7 From Words to Symbols Suggest to practice:
Stop to think 1.1 P5 Stop to think 1.2 P6 Stop to think 1.3 P13 Stop to think 1.4 P15 Stop to think 1.5 P28 Example 1.2 P 12 Example 1.4 P 16 Example 1.6 P 17 Example 1.8 P 22 Example 1.9 P 23 Example 1.10 P 27 1.1 Motion Diagram Motion is defined as the change of an object's position with time The right picture is showing a car positions at several equally spaced instants of time. It is motion diagram I Object moving with constant speed Ball slowing down as it rises And speeding up as it falls 1.2 Particle Model Particle model of motions is a simplification in which we treat a motion object as if all of its mass were concentrated at a single point. 1.3 Position and Time Change in Position t t t t r = r 1 - r 0 r is Displacement. Vector and Vector addition Application to Motion Diagrams Velocity
distance average speed = time interval spent traveling r V ( avg ) = t
In Physics the distinction between speed and velocity is very important. Speed is scalar (how fast); velocity Is vector (how fast and in which direction). Motion diagrams with velocity vector Motion diagram of a ball The average velocity vectors are found by connecting to dots with arrows. Relating position to velocity Acceleration Average acceleration v a ( avg ) = t t A particle undergoes acceleration which moving a
from 1 to point 2. Which of the choice shows the t velocity v2 Examples of Motion Diagrams Please practice examples 1.41.8 (page 18--20). Example 1.4 Skiing through the wood Position vs time graphs From Words to Symbols Sketch the situation Establish a coordinate system t t t t Define symbols. ex. Vx Vy Vo Vf List known information Some quantities are implied by the problem, rather than explicitly given. Others are determined by your choice of coordinate system. Identify the desired unknowns Units and significant figures Three basics SI unit Convert the following to SI units 60mi/h = 60mi 1600m / mi = 27 m / s 1h 3600 s / h Alcohol mass density 0.81g/cm =
3 0.81g 10 - 3 kg / g 2 3 = 8.1kg 10 / m 3 -6 3 3 (cm ) 10 (m / cm ) ...
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- Fall '09