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Ch 2 : kinematicsCh 2 : kinematics
Ideas about describing motion: Ideas about describing motion: speed, velocity, accelerationspeed, velocity, acceleration
KinematicsKinematics
• Ave speed: s = total distance/total time
• Run 3 miles at 10 mi/hr, then crawl 3 miles at 1 mi/hr. What is your average speed?
KinematicsKinematics
• Speed vs. velocity
• These words often are used interchangeably but there is a difference.
• Velocity is a vector, meaning it has direction. Speed is just how fast something is traveling.
KinematicsKinematics
• Acceleration: a word we use frequently but is often misunderstood.
• Acceleration: how the velocity of something is changing. It’s the rate of change of a rate of change (huh?)
• A speed of 1 m/s is very different from an acceleration of 1m/s/s.
• We will only solve problems which have constant or uniform acceleration
KinematicsKinematics
• Importance of graphing and being able to interpret graphical data concerning motion.
• A graph gives you a quick representation.
• Slopes of graphs tell you rates: slope of a distance/time graph gives you speed, slope of a velocity/time graph gives you acceleration.
KinematicsKinematics
• Whenever possible make a quick graph of a motion problem.
• A velocity/time graph can be used to find distance (often easier than plugging in numbers into equations).
• The area under a velocity/time graph gives you the distance travelled.
KinematicsKinematics
• “standard equations” for motion at constant acceleration
• V = v0 + at
• X = x0 + v0t + ½ a t2
• V2 = v02 + 2a (x – x0)
• V(ave) = (v + v0)/2
• Which equation you use depends on what you know.