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 Exploring Objects in Motion Physics is a science that is based upon experimental observations. Many of the basic principles used to describe and understand mechanical systems, such as objects in linear motion, can be applied later to describe other more complex natural phenomena. How can you measure the speed of the vehicles in a video clip?

Question
What type of measurements could be made to find the speed of a vehicle?

• Observe the motion of the vehicles seen in the video.
• Describe the motion of the vehicles.
• Collect and organize data on the vehicle's motion.
• Calculate a vehicle's speed.

Internet access is required.
watch or other timer

1. View the Chapter 1 lab video clip (Quicktime Format Broadband) / video clip (Quicktime Format Dial-Up)

2. The video footage was taken in the midwestern United States at approximately noon. Along the right shoulder of the road are large, white, painted rectangles. These types of markings are used in many states for aerial observation of traffic. They are placed at 0.322-km (0.2-mi) intervals.

3. Observe What type of measurements might be taken? Print the Data Table. Record your observations of the surroundings, other vehicles and markings in the Data Table. On what color vehicle is the camera located, and what color is the pickup truck in the lane to the left?

4. Measure and Estimate View the video again and look for more details. Is the road smooth? In what direction are the vehicles heading? How long does it take each vehicle to travel two intervals marked by the white blocks? Record your observations and data in the Data Table.

 Summarize your qualitative observations. Summarize your quantitative observations. Make and Use Graphs Graph both sets of data on one pair of axes. Estimate What is the speed of the vehicles in km/s and km/h? Predict How far will each vehicle travel in 5 min? Measure What is the precision of the distance and time measurements? Measure What is the precision of your speed measurement? On what does it depend? Use Variables, Constants, and Controls Describe the independent and the dependent variables in this experiment. Compare and Contrast Which vehicle's graph has a steeper slope? What is the slope equal to? Infer What would a horizontal line mean on the graph? A line with a steeper slope?
 Speed is distance traveled divided by the amount of time to travel that distance. Explain how you could design your own experiment to measure speed in the classroom using remote-controlled cars. What would you use for markers? How precisely could you measure distance and time? Would the angle at which you measured the cars passing the markers affect the results? How much? How could you improve your measurements? What units make sense for speed? How far into the future could you predict the cars' positions? If possible, carry out the experiment and summarize your results.
 When the speedometer is observed by a front-seat passenger, the driver, and a passenger in the rear driver's-side seat, readings of 90 km/h, 100 km/h, and 110 km/h, respectively, are observed. Explain the differences.

Post your experiment in the Share Your Data fields for measuring speed in the classroom using remote-controlled cars. Include your list of materials, your procedure, and your predictions for the accuracy of your lab. If you actually perform your lab, post your data and results in the Data Table below. See example.

Materials

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Data Table
 Trial Displacement (m) Time (s) Speed (m/s) 1. 2. 3. Average
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