PHY 101 1st Edition Lecture 4 Chapter 2 Motion in One Dimension I Definitions II Kinematics III Displacement Chapter 2 Motion in One Dimension Continued II Velocity Speed A Constant Velocity B Varying Velocity C Instantaneous Velocity III Acceleration a Average Acceleration b Instantaneous Acceleration Current Lecture Displacement of an object is not the same as the distance it travels Ex A car travels a full circle and goes back to its original position o Displacement 0 o Distance 2 r 2 2 Velocity and Speed Velocity is a vector Speed is scalar Both explain how fast an object moves Average speed vs average velocity SI units m s o Avg speed path length elapsed time o Avg velocity displacement time difference x t where x displacement Ex A receiver runs 40 s down a 100 yard football field to return to its original position o Avg speed 200yd 40s 5 yd s o Avg velocity 0yd 40s 0 yd s Constant velocity graph o Position y axis vs time x axis is a straight line o Avg velocity is the slope of the line o constant v x v t Varying velocity o Same as the slope of the straight line joining two point on the curve 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 Instantaneous velocity o Velocity is equal to the limit as t approaches 0 of x t t gets infinitely smaller o SI units m s o Graph The slope of the line tangent to the curve gives you the instantaneous velocity o for constant velocity instantaneous velocity is equal to the average velocity 2 3 Acceleration Things don t always move with constant velocity o Once velocity changes you have acceleration Acceleration rate of change of an object s velocity o a v t v f vi tf ti SI units m s2 Ex Velocity changes from 10 m s to 20 m s in 2 seconds What is the acceleration A 20m s 10m s 2s 0s 10m s 2s 5m s2 in the positive east direction Average acceleration o Acceleration is a vector o Ex Velocity changes from 10m s to 20m s in 2 seconds What is the acceleration A 20m s 10m s 2s 0s 10m s 2s 5m s 2 in the negative west direction o Even though the acceleration is negative the speed is still increasing since speed has no direction it isn t affected by the direction of acceleration o Negative acceleration DOES NOT mean deceleration Instantaneous acceleration o Acceleration at a given time o It is equal to the limit as t approaches 0 of v t o SI unit m s2 o Graph Velocity vs Time Instantaneous acceleration slope of the line tangent to the curve
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