PHY 102 1nd Edition Lecture 8 Outline of Last Lecture I II III Motion Uniformly Accelerated Motion UAM Blue Book 3 1 Outline of Current Lecture I Kinematics Current Lecture I Kinematics a Motion of an object is always described in relation to an observer The object and the observer are considered as points b Studies the three fundamental qualities i Position vector ii Velocity vector iii Acceleration vector c Vector arrow d Position vector an arrow with its tail at the observer and its tip at the moving object i If the position vector changes we say the object is moving relative to the observer ii Observer is not moving 1 Driving down the highway you can consider yourself the observer which means you aren t moving but the highway is iii It is wrong to say that the car is moving but the tree is not You are not saying who the observer is has to be relative 1 You can say the car moves relative to the tree or the tree moves relative to the car iv All objects that don t move relative to one another are said to belong to the same reference frame RF These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 1 The hardest thing to get used to is the fact that earth is not our only RF v Motion of an object relative to an observer e Displacement the change in the position vector i Final position vector initial position vector ii It is the arrow that connects the initial position to the final position the latter changing with time r rf ri Displacement is always a straight arrow Distance is the length of the path traveled curvy line iii The same as long as the observers are in the same RF f Average velocity i What you get when you divide displacement vector by time v avg r t 1 When the time becomes infinitesimally short you get instantaneous velocity g Average speed i When you divide the length of the path by time you get the average speed vavg distance t 1 When the time becomes infinitesimally short you get instantaneous speed h For a car the magnitude of the instantaneous velocity is what you read on the speedometer and its direction is the direction of the car s motion
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