DistanceTimeVelocitySEm on 2022-09-27 19_35_10

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Dallas County Community College *

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MECHANICS

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Physics

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Dec 6, 2023

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Name: Date: Student Exploration: Distance-Time and Velocity-Time Graphs [NOTE TO TEACHERS AND STUDENTS: This lesson was designed as a follow-up to the Distance-Time Graphs Gizmo. We recommend you complete that activity before this one.] Vocabulary: displacement, distance traveled, slope, speed, velocity Prior Knowledge Questions (Do these BEFORE using the Gizmo .) Dora runs one lap around the track, finishing where she started. Clark runs a 100-meter dash along the straight side of the track. 1. Which runner traveled a greater distance? Dora 2. Which runner had a greater change in position, start to finish? Clark Gizmo Warm-up The Distance-Time Graphs Gizmo shows a dynamic graph of the position of a runner over time. The Distance-Time and Velocity-Time Graphs Gizmo includes that same graph and adds two new ones: a velocity vs. time graph and a distance traveled vs. time graph. The graph shown below (and in the Gizmo) shows a runner’s position (or distance from the starting line) over time. This is most commonly called a position-time graph . Check that the Number of Points is 2. Turn on Show graph and Show animation for both Runner 1 and Runner 2 . 1. Drag the points to create the graph shown to the right. ● Runner 1 ’s line (the red one) should have endpoints at (0, 0) and (4, 40). ● Runner 2 ’s line (the blue one) should have endpoints at (0, 40) and (4, 20). 2. Click the green Start button on the stopwatch. Watch the two runners carefully. In what two ways are the runners’ motions different? Despite the fact they are both moving, the blue

character, Runner 2, is running at a slower pace in the opposite direction than the red character, Runner 1, depicted.

Activity A: Velocity-time graphs Get the Gizmo ready: ● Click the red Reset button on the stopwatch. ● Change the Number of Points to 5. ● Turn off Show graph and Show animation for Runner 2 . Speed is a measure of how fast an object moves, regardless of direction. Speed can never be negative. Velocity describes both speed and direction, and can be positive or negative. 1. In the Gizmo, make a position-time graph for Runner 1 with the following features: ● There is at least one major change in speed. ● There is at least one major change in direction. Click the green Start button and watch the runner run. Adjust your graph if needed to meet the requirements. Sketch your graph to the right. 2. Where was the runner each second? Based on your graph, fill in all except the final column in the table below. (Leave the velocity column blank for now.) Label any numbers with units. Time Position at end of time interval (m) Distance moved this time interval (m) To the left or right? Velocity this time interval (m/s) 0 – 1 sec 40m 40m right 40m/s 1 – 2 sec 10m 30m left -30m/s 2 – 3 sec 30m 20m right 20m/s 3 – 4 sec 0m 30m left -30m/s 3. To calculate the velocity for each time interval, first calculate the speed of the runner in that interval (speed = distance ÷ time). If the direction is left to right, velocity is positive. If the direction is right to left, velocity is negative. Fill in the velocity column of the table above. Use units (m/s). When this runner is running to the left (negative velocity), what does his position-time graph look like? When the runner is running left, or at a negative velocity, on the runner’s position-time graph, the slope becomes negative.

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(Activity A continued on next page)

Activity A (continued from previous page) 4. Slope is the steepness of a graph. To find the slope of a line, divide the change in y -value (rise) by the change in x -value (run). Like velocity, slope can be positive, zero, or negative. Fill in the slope of each segment of your position-time graph, along with the runner’s velocity during each time interval, in the table below. Time interval Slope Velocity (m/s) 0 sec – 1 sec m=40 40m/s 1 sec – 2 sec m=-30 -30m/s 2 sec – 3 sec m=20 20m/s 3 sec – 4 sec m=-30 -30m/s 5. Examine your velocities and the position-time graph you made. How is the slope of a position-time graph related to the velocity of the runner? According to the position-time graph, the velocity and slope of the graph are directly related as they have the same data. 6. On the left side of the Gizmo, select the VELOCITY-TIME GRAPH tab. Use the green probes to compare the velocity-time graph to the position-time graph. A. How does a velocity-time graph show that a runner is moving fast? This graph shows that a runner is moving fast by graphing the velocity of the runner per second. B. How does a velocity-time graph show that a runner is moving from left to right? The graph shows that a runner is moving from left or right by going in between positive and negative data points. 7. To the right is a position-time graph of a runner. First, sketch what you think his velocity-time graph will look like on the blank axes at the far right.

Then check your answer in the Gizmo. I was right

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Activity B: Velocity and position Get the Gizmo ready: ● Set the Number of Points to 3. ● Turn on Show graph and Show animation for both Runner 1 and Runner 2 . 1. In the Gizmo, make the position-time graphs shown below. Click the green Start button and watch the runners run. Sketch what you think their velocity-time graphs look like on the second set of axes. (If you can, use a red line for runner 1, and a blue line for runner 2.) Then select the VELOCITY-TIME GRAPH tab in the Gizmo. Sketch the actual graph on the third set of axes below. Position-time graph Velocity-time (predicted) Velocity-time (actual) 2. Make any position-time graphs you want for Runners 1 and 2 . Sketch them below. Then do the same thing – sketch what you think their velocity-time graphs look like, and then check. Position-time graph Velocity-time (predicted) Velocity-time (actual) 3. Compare the velocity-time graphs to their related position-time graphs.

A. When do two different position-time graphs have matching velocity-time graphs? Two different position-time graphs only have matching velocity-time graphs if their slopes are the exact same. B. What information is missing from a velocity-time graph? In a velocity-time graph, the location and distance traveled are missing. Activity C: Distance and displacement Get the Gizmo ready: ● Turn off Show graph and Show animation for Runner 2 . 1. Create the position-time graph for Runner 1 shown at right. Then fill in the blanks below to describe what you think the runner will do, based on that graph. The runner will run 40 meters in the first 2 seconds, with a velocity of 20 m/s. His direction will be from left to right. Then he will run 10 meters in the next 2 seconds, with a velocity of _________ m/s. His direction will be from right to left . Click the green Start button and watch the runner go. Were you correct? Yes 2. Two students, Gina and Walter, are discussing the runner whose graph is shown above. ● Gina says the runner moved more than 40 meters. ● Walter says the runner moved less than 40 meters. A. Who do you think is right? Gina is right B. Explain your answer. I believe Gina is right because even though the runner ran in two different directions, he still ran those meters. This means the runner would have run 40 meters in the first two seconds in one direction and the 10 meters in another direction, totalling to be a total of 50 meters ran.

3. On top of the left half of the Gizmo, select the DISTANCE TRAVELED tab. A. What was the total distance traveled by the runner after 4 seconds? 50 meters B. Displacement is equal to the difference between the starting and ending positions. Displacement to the right is positive while displacement to the left is negative. What is the displacement shown by the graph at the top of the page? 30 meters (Activity C continued on next page)

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Activity C (continued from previous page) 4. In the Gizmo, create a position-time graph of a runner with these characteristics: ● travels a distance of 60 meters in 4 seconds ● has a displacement of +10 meters Sketch your graph on the blank axes to the right. 5. Look at the graph you made in question 4. Think about the speed of that runner. A. What was the runner’s speed for the first 2 seconds? 17.5m/s B. What was the runner’s speed for the last 2 seconds? 12.5m/s C. What was the runner’s average speed over all 4 seconds? 15m/s 6. Now think about the velocity of the runner in question 4. A. What was the runner’s velocity for the first 2 seconds? 17.5m/s B. What was the runner’s velocity for the last 2 seconds? -12.5m/s C. What was the runner’s average velocity over all 4 seconds? 2.5m/s 7. Suppose you knew the time, displacement, and total distance traveled for a runner. A. How would you calculate the runner’s average speed? To find the average speed, I would take the total distance traveled by the runner and divide it by the time it took to get from the starting point to the ending point. B. How would you calculate the runner’s average velocity? To find the average velocity, I would use the runner’s displacement and divide it by the time it took to get from the starting point to the ending point.

8. To the right is a graph of a runner. Calculate the values below for this runner. Include appropriate units. A. Distance traveled: 100m B. Displacement: 20m C. Average speed: 25m/s D. Average velocity: 5m/s

DistanceTimeVelocitySEm on 2022-09-27 19_35_10

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