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## 9/30/14 Velocity graphs

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**9/30/14 Velocity graphs**• Science podcast: Changing Foliage • Discuss motion graphs from running activity • What do constant velocity and changing velocity graphs look like? • Fan cart activity • Making a velocity vs time graph**Learning Objectives**• Sketch a graph of uniform, speeding up, or slowing down motion • Apply the definition of velocity to solve for an unknown • Interpret the components of the equation of a velocity vs time graph**Constant velocity**• The car moves equal intervals in equal amounts of time. • Car is not speeding up or slowing down (or changing direction). • Graph is a straight line. See example. • How do we know the car is not speeding up or slowing down between data points?**Increasing velocity**• The car moves increasing distances in equal amounts of time. • Graph is a upward curve. • How do we know the car is not constant or slowing down between data points? • Compare different cars. • Go over homework from yesterday**Fan Cart Activity**• Today you will get a car that speeds up. Please be careful of the propeller. It can pinch your finger. • You will also get a tape timer, a device that puts a mark on a paper every 0.1 s or 0.025 s. • Attach about 1 m of tape to the back of your cart. • Make a data table with about 10 position and corresponding time values. Don’t use every point! • Use Excel to make a position vs. time and velocity vs. time graph for your car. I have put an Excel worksheet template on the course website • http://cwuphys106.pbworks.com/**Graphing motion**• To make a position vs time graph, plot time along the x-axis and position along the y-axis. • To make a velocity vstime graph, plot time along the x-axis and velocity along the y-axis. • Determine the best fit curve using Excel (either linear or polynomial) • Email to palmquis@cwu.edu Sample data**Sample Velocity vs. time graph**• The line equation is y = mx + b • What are y, x, m, b? • Here y is velocity, x is time, m describes the rate of speeding up, and b is initial velocity**Revisit Motion pretest**• Does today’s activity help us answer any of the Motion pretest items? • How do we know if there is acceleration? • When the velocity does not change. • Item 6 on the pretest asks about this.**Motion pretest 2014**Number of responses for each choice. Correct answer in red.**Motion pretest 2013**Number of responses for each choice. Correct answer in red.**Motion pretest 2012**Number of responses for each choice. Correct answer in red.**Motion pretest 2011**Number of responses for each choice. Correct answer in red.**Motion pretest 2010**Number of responses for each choice. Correct answer in red.