Ch 2 : kinematicsCh 2 : kinematics

Ideas about describing motion: Ideas about describing motion: speed, velocity, accelerationspeed, velocity, acceleration

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• 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?

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• 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

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• 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.

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• 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.

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• “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.