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08/23/10 - Describing Motion (Kinematics)
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 | What does it mean to say something is moving?
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 | It changes its position (with respect to some reference frame) with time.
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 | What quantities are used to describe motion?
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| Position (relative to some reference point)
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| Distance traveled and displacement
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| Distance is how far you've traveled.
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| Displacement is the distance and direction you've moved relative to your starting point.
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| Suppose you moved in a circle with a circumference of 10 meters. What distance have you traveled? What is your displacement?
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| Speed is the distance you've covered per unit time. For example, if you drove 30 miles in half an hour, your average speed would be 30 miles/0.5 hour = 60 miles/hour.
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| Velocity is your displacement / time. Since displacement includes direction, velocity also includes direction. For example, if you drove 30 miles south in half an hour, your average velocity would be 30 miles south/0.5 hour = 60 miles/hour south.
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| What if you drove 30 miles around a circle and wound up back at your starting point after 0.5 hours?
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| What is your average speed?
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| What is your average velocity?
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| Changes in velocity and acceleration
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| Acceleration occurs whenever your velocity changes
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| If your velocity increases, then your acceleration is positive.
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| If your velocity decreases, then your acceleration is negative.
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| The magnitude of your acceleration is the change in velocity / change in time
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| Your car has two pedals for acceleration. What are they?
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| This is what you calculate for a trip to LA
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| I drove 400 miles due south and it took me 8 hours, so my average velocity was vavg = 400 miles south / 8 hours = 50 miles/hour south. Note that the magnitude of my average velocity (50 miles/hour) is my average speed.
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| Your speedometer shows you the magnitude of your instantaneous velocity (i.e., your speed right this instant).
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| Graphs of position vs. time
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| Sketch the Position-Time graph for a woman who walks from her house to a mailbox on the corner and then returns to her house.
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| Sketch the Position-Time graph for a woman who walks from her house to a mailbox on the corner and then returns to her house but stops to smell some roses on her way back.
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| Sketch the Position-Time graph for a kid who walks from her house to a mailbox on the corner and then runs back to her house.
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| Graphs of velocity vs. time
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| Sketch the Velocity-Time graph for a woman who walks from her house to a mailbox on the corner and then returns to her house.
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| Sketch the Velocity-Time graph for a woman who walks from her house to a mailbox on the corner and then returns to her house but stops to smell some roses on her way back.
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| Sketch the Velocity-Time graph for a kid who walks from her house to a mailbox on the corner and then runs back to her house.
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| A car travels 1 mile at a constant velocity of 1 mile/hour. It then travels another mile at 1000 miles/hour (a jet car). What is the average velocity for the whole trip?
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