Clock Reading (t) Position (x) Clock Reading (t) Position (x)

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1 How Fast are you Moving? 2.1 Observe and represent Find a starting position on the floor. You will need to use 2 cars for this experiment (try to use one fast and one slow). Practice releasing the car with one of your partners. For each run, you will mark the position of the car at each second. a) Discuss with your teammates and decide on a method for keeping time and marking the location of the car for each second. Practice the method until you are comfortable with it. When you are ready, start with one car; record the data in a table like the one below. b) Next, repeat the experiment for the slow car and record the data in a table. (You may need to trade with another group). Car 1 Car 2 Clock Reading (t) Position (x) Clock Reading (t) Position (x) c) What are the physical quantities measured in this experiment? What units of measure did you use? d) Explain the differences between these two ideas.

2 2.2 Represent and Reason a) Greg, Kim, Nahin and Mitchell (at rest with respect to each other) collected data for the motion of the same car. They each represented the data differently. Examine the four representations below; select a representation that would best represent the position of the car as a function of time. Explain. Greg Nahin Kim Mitchell b) Discuss your choice and reasoning with your lab partners.

3 c) Represent the motion of the cars with a graph (plot the data from each car on the same axes) using the data collected in activity. The position of the car is recorded on the vertical axis and the clock reading on the horizontal axis. Dot Diagram Graph d)draw a trend line for each car on the graph you drew in part (c). What information can you learn about the motion of the car from the graph? Explain. 2.3 Represent and Reason a) Compare the trend lines of the two cars. How are they different? b) Find the slopes of the two lines. Explain how you found the slope. What name could you give to the slope? c) Explain what it means if the slope is positive or negative. d) What is the velocity of each car in your experiment? How did you do that? e) Write a function x(t) for the fast car and a separate function for the slow car. What role does the trend line play and what role does the y-intercept play in writing this function?

4 Homework 2.4 Practice a) A car moved from to. Draw a picture with the coordinate axis, zero point and the b) A car moved from to. Draw a picture with the coordinate axis, zero point and the c) A car moved from to. Draw a picture with the coordinate axis, zero point and the d) A car moved from to. Draw a picture with the coordinate axis, zero point and the 2.5 Practice In the previous example, the time interval during which the position change occurred t = 1.5hr. Determine the velocity and the speed of the car for each. What does it mean if velocity is positive? Negative? To answer relate to the direction of the x axis. 2.6 Analyze a) The graph below shows the motion of a football player during 20 seconds. What is the player s position at the point shown with the triangle on the graph? Choose the answer that you think is best. I) 2.5 yards; II) 10 yards; III) 35 yards; IV) 25 yards. b) How far did the player travel from the beginning of observations? I) 2.5 yards; II) 20 yards; III) 35 yards; IV) 25 yards. c) What happened at the 0 clock reading: I) The player started moving; II) The player was passing the mark of 45 yards; III) The player was moving in the negative direction; IV) both II and III are correct.

5 d) Which answer best describes the player s motion at the point indicated by the triangle on the graph? I) The player is moving at constant speed: II) The player encountered a dip and is moving slightly downhill; III) The player is slowing down; IV) The player stopped. 2.7 Represent and Reason Two objects are moving in the same direction. The speed of one is 5 m/s and the speed of the other is 10 m/s. When you start observing them, they pass the same location at the same time. a) Draw dot diagrams for two objects. b) Represent their motions with position versus time graphs. Use the same scale for both objects. c) The following are functions that could describe the motion of object X1 and Object X2. Choose a combination that looks correct to you: I) x1 = (5 m/s) + t; x2 = (10 m/s) + t; II) x1 = (5 m/s)t; x2 = (10 m/s)t; III) x1 = t(5 m/s); x2 = t(10 m/s); IV) both II and III are correct. d) How long will it take each object to travel 276 m? e) How far from each other will they be in 10 seconds? 20 seconds after you start observing them? Reflect: What did you learn in this lesson? Can you explain to your friends how the slope of the position versus time function is related to the object s velocity? What does it mean if velocity is positive? What does it mean if it negative?