PHY 101 1st Edition Lecture 4 Chapter 2: Motion in One DimensionI. DefinitionsII. KinematicsIII. DisplacementChapter 2: Motion in One Dimension ContinuedII. Velocity, SpeedA. Constant VelocityB. Varying VelocityC. Instantaneous VelocityIII. Accelerationa. Average Accelerationb. Instantaneous AccelerationCurrent 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 positiono Displacement = 0o Distance = 2Πr2.2 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 timeo Avg. velocity = displacement/ time difference = Δx/ Δt where Δx = displacement- Ex. A receiver runs 40 s down a 100 yard football field to return to its original positiono Avg. speed = 200yd/ 40s = 5 yd/so Avg. velocity = 0yd/ 40s = 0 yd/s- Constant velocity grapho Position (y-axis) vs. time (x-axis) is a straight lineo Avg. velocity is the slope of the lineo ** constant v: Δx = v(Δt)- Varying velocityo Same as the slope of the straight line joining two point on the curveThese 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 velocityo Velocity is equal to the limit as Δt approaches 0 of Δx/Δt Δt gets infinitely smallero SI units: m/so 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 velocityo Once velocity changes, you have acceleration- Acceleration: rate of change of an object’s velocityo [a] = Δv/Δt = (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 accelerationo Acceleration is a vectoro 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/s2 [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 accelerationo Negative acceleration DOES NOT mean deceleration- Instantaneous accelerationo Acceleration at a given timeo It is equal to the limit as Δt approaches 0 of Δv/Δto SI unit: m/s2o Graph: Velocity vs. Time Instantaneous acceleration = slope of the line tangent to the
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