Free-Fall Laboratory Answer Key Vocabulary: acceleration, air resistance, free fall, instantaneous velocity, terminal velocity, velocity, vacuum Prior Knowledge Questions (Do these BEFORE using the Gizmo.) [Note: The purpose of these questions is to activate prior knowledge and get students thinking. Students are not expected to know the answers to the Prior Knowledge Questions.] 1. Suppose you dropped a feather and a hammer at the same time. Which object would hit the ground first? Answers will vary. [The hammer would hit the ground first.] 2. Imagine repeating the experiment in an airless tube, or vacuum. Would this change the result? If so, how? Answers will vary. [In a vacuum, both objects would hit the ground at the same time.] Gizmo Warm-up The Free-Fall Laboratory Gizmo allows you to measure the motion of an object in free fall. On the DESCRIPTION tab, check that the Shuttlecock is selected, the Initial height is 3 meters, and the Atmosphere is Air. 1. Click Play ( ) to release the shuttlecock. How long does it take to fall to the bottom? 0.90 seconds 2. Select the GRAPH tab. The box labeled h (m) should be checked, displaying a graph of height vs. time. What does this graph show? The height decreases over time. 3. Turn on the v (m/s) box to see a graph of velocity vs. time. Velocity is the speed and direction of the object. Velocity is also referred to as instantaneous velocity. Because the shuttlecock is falling downward, its velocity is negative. Does the velocity stay constant as the object drops? No 4. Turn on the a (m/s/s) box to see a graph of acceleration vs. time. Acceleration is the rate at which the velocity changes over time. What does this graph show? Acceleration starts at about -10 m/s/s, but gets closer to 0 as the shuttlecock falls. This study source was downloaded by 100000808701186 from CourseHero.com on 06-03-2022 17:34:21 GMT -05:00 https://www.coursehero.com/file/70189294/FreeFallSE-Keypdf/ 2019 Activity A: Falling objects Get the Gizmo ready:  Click Reset ( ).  Select the DESCRIPTION tab. Question: What factors affect how quickly an object falls? 1. Observe: Drop each item through Air from a height of 3 meters. Record how long it takes to fall below. For the tennis ball, try to click Pause ( ) when it hits the ground. Shuttlecock Cotton ball Tennis ball Rock Pebble 0.90 s 1.36 s ~0.81 s 0.79 s 0.80 s 2. Form a hypothesis: Why do some objects fall faster than others? Hypotheses will vary. 3. Predict: A vacuum has no air. How do you think the results will change if the objects fall through a vacuum? Predictions will vary. 4. Experiment: On the Atmosphere menu, select None. Drop each item again, and record the results below. Shuttlecock Cotton ball Tennis ball Rock Pebble 0.78 s 0.78 s 0.78 s 0.78 s 0.78 s 5. Analyze: What happened when objects fell through a vacuum? Every object took the same amount of time to fall to the ground. 6. Draw conclusions: Objects falling through air are slowed by the force of air resistance. Which objects were slowed the most by air resistance? Why do you think this is so? The cotton ball and shuttlecock were slowed the most by air resistance. They were slowed the most because they were the lightest and largest objects. (Activity A continued on next page) This study source was downloaded by 100000808701186 from CourseHero.com on 06-03-2022 17:34:21 GMT -05:00 https://www.coursehero.com/file/70189294/FreeFallSE-Keypdf/ 2019 Activity A (continued from previous page) 7. Calculate: Select the Shuttlecock. Check that the Initial height is 3 meters and the Atmosphere is None. Click Play and wait for the Shuttlecock to fall. Select the BAR CHART tab and turn on Show numerical values. A. How long did it take the shuttlecock to fall to the bottom? 0.78 seconds B. What was the acceleration of the shuttlecock during its fall? -9.81 m/s/s C. What was the velocity of the shuttlecock when it hit the bottom? -7.68 m/s (Note: This is an example of instantaneous velocity.) D. What is the mathematical relationship between these three values? The final velocity was close to the product of acceleration and time: -9.81 m/s/s · 0.78 s = -7.65 m/s, which is close to -7.68 m/s [The relationship is exact. The values are not exactly equal because of rounding.] 8. Make a rule: If the acceleration is constant and the starting velocity is zero, what is the relationship between the acceleration of a falling body (a), the time it takes to fall (t), and its instantaneous velocity when it hits the ground (v)? The instantaneous velocity is equal to acceleration multiplied by time. Express your answer as an equation relating v, a, and t: v = at 9. Test: Click Reset. On the DESCRIPTION tab, set the Initial height to 12 meters. Click Play. A. How long did it take for the shuttlecock to fall 12 meters? 1.56 seconds B. Assuming the acceleration is still -9.81 m/s2 , what is the instantaneous velocity of the shuttlecock when it hits the ground? Show your work below. -9.81 m/s/s · 1.56 s = -15.3 m/s v = -15.3 m/s C. Select the BAR CHART tab. What is the final velocity of the shuttlecock? -15.35 m/s D. Does this agree with your calculated value? Yes, this agrees with the calculated value. [Any differences are due to rounding.]