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08/24/09 - Chapter 2 - Describing Motion |
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;){kind=small} | 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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;){kind=small} | What quantities are used to describe motion? |
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| Position (relative to some reference point) |
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;){kind=small} | 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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;){kind=small} | Speed and velocity |
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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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;){kind=small} | 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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;){kind=small} | Average velocity |
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;){kind=small} | This is what you calculate for a trip to LA |
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| I drove 400 miles and it took me 8 hours, so my average velocity was vavg = 400 miles / 8 hours = 50 miles/hour. |
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;){kind=small} | Instantaneous velocity |
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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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;){kind=small} | Graphs of position vs. time |
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;){kind=small} | Example 1: |
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;){kind=small} | Example 2: |
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;){kind=small} | Example 3: |
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;){kind=small} | Example 4: |
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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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;){kind=small} | Example 5: |
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;){kind=small} | Graphs of velocity vs. time |
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;){kind=small} | Example 1: |
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;){kind=small} | Example 2: |
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;){kind=small} | Example 3: |
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;){kind=small} | Example 4: |
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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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;){kind=small} | Example 5: |
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;){kind=small} | Quiz |
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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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