TEACHING SUGGESTIONS DOING THE ACTIVIT Y GETTING STARTED FOLLOW-UP. Decelerating Safely Activity 25

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1 Decelerating Safely Activity 25 TEACHING SUGGESTIONS GETTING STARTED 1. Review the concept of deceleration as it relates to acceleration. Ask the class to think about their experiences as passengers in cars. Ask, How do you know when you are accelerating while traveling in a car? Students should describe situations such as starting up from a stoplight or passing a vehicle. They may know acceleration is happening when they have the feeling of being pushed back in the seat while the car accelerates forward. Ask, How do you know when you are decelerating while traveling in a car? A vehicle that is decelerating, such as when a car comes to a stop, will make passengers feel like they are thrown forward as the car accelerates backward (decelerates). Use these examples to review the concept of acceleration and deceleration but also to reinforce the role of inertia within moving cars. It is a person s inertia that makes him or her continue to travel during deceleration (that thrown forward feeling). The same reasons cause passengers to feel like they stay behind and get pushed against the seatback during acceleration. Let students know that in this activity they will investigate the effects of decelerations in car collisions. 2. (LITERACY) Use a Talking Drawing to elicit students current knowledge. Before students start the Reading, introduce Student Sheet 25.1, Talking Drawing: Safety Features. The Talking Drawing literacy strategy helps students construct meaning by asking them to draw images on a particular topic both before and after reading about it, and then having them explain how their drawings have changed as a result of the reading. These parts of the Talking Drawing are completed after students have completed the activity. Explain to students that they can use this prereading strategy in numerous places throughout the course. Ask students to complete the first part of Student Sheet DOING THE ACTIVIT Y 3. (LITERACY) Students read about the safety features in vehicles. During the reading, students are provided an opportunity to improve their performance in reading comprehension, particularly of informational text. Student Sheet 25.2, Three-Level Reading Guide: Decelerating Safely, guides students through the text and through three levels of understanding: literal, interpretive, and applied. Students look at a list of statements and determine which ones are supported by the text. This also provides an opportunity for students to apply their prior experiences to understand the meanings of the terms that they will encounter in this activity and in the unit. For more information on Three- Level Reading Guides and on Talking Drawings, see the literacy section of Teacher Resources II: Diverse Learners. Possible responses to the reading guide are shown on the next page. Note that the statements 3a, 3b and 3c (applied level of understanding) do not have a single correct response. Students may interpret information differently and agree or disagree with each statement. Whatever their perspective, it is important that students be able to explain and support their positions. FOLLOW-UP 4. Students revise their earlier ideas about vehicle safety. Review the Analysis Questions with students. Emphasize that the major principles behind safety features are that slower deceleration results in a reduction in force and a larger area of impact results in a reduction of the force per unit area or pressure. Some devices can mitigate injuries and fatalities in more than one way. Seatbelts, for example, help reduce the collision force by increasing the area of the force across a person s body, redirecting the force from the head to the broader torso, and by decelerating the body over more time than if it hit the steering wheel or dashboard. 237

2 Activity 25 Decelerating Safely When discussing Analysis Question 4, explain that the steady fatality rate has been attributed to many things and that no one factor seems to stand out as a cause. Some of the factors that tend to keep the fatality rate about the same are: more distractions, such as cell phones and handheld electronic devices a larger number of older drivers lack of seatbelt use (almost 40% of all passengers killed are not wearing seatbelts) reintroduction of higher speed limits less car uniformity (mass, bumper height) when vehicles collide At the end of the activity, have students complete the second part of Student Sheet 25.1, Talking Drawing: Safety Features. Their ideas should reflect the content of the reading and the class discussion. For example, a student may add more safety features, such as crumple zones and padded dashboards. When everyone has finished, have students share their work and discuss with the class how their ideas have changed. SUGGESTED ANSWERS TO QUESTIONS 1. Choose one of the safety features described in the reading. Use the terms inertia, force, and deceleration to describe how the safety feature helps keep people safe in a collision. Answers will vary. Students should explain that on impact, the car decelerates very rapidly, but inertia keeps objects within the car, including people, moving at a higher speed. They should then explain how their chosen safety feature helps decelerate the body more gradually, so that there is an increase in time and a reduction in force. 2. As a collision is about to happen, if you had enough time to chose between hitting a large haystack or a telephone pole, which one would you choose to hit? Explain why in terms of force and deceleration. Hitting a haystack would be more desirable because the collision with the more rigid and firmly attached telephone pole would cause the car to decelerate much more rapidly and produce a much greater impact force. The area of impact for the haystack is much larger than a telephone pole so the force of the haystack is decreased because it is distributed over a larger area. 3. In the accident mentioned in Activity 14, Choosing a Safe Vehicle, Noah s family car had old tires that were worn down. Explain how this could have contributed to the car accident. Tires are designed to optimize the friction between them and the road so that the car gets good traction, handles well, and can stop quickly. As tires wear down, their ability to do all these safety-related things decreases and the braking distance increases. 4. Reflection: Since the 1920 s, the rate of fatalities per billion miles traveled has dropped steadily. However, the rate has been about the same for the past 20 years. Why do you think this is? Answers will vary but should include ideas such as the major gains in safety features occurred before the rate settled, there are more distractions on the road today that negate the effects of improved safety features, there is a minimum of bad drivers so the rate cannot drop indefinitely, and weather and other factors will prevent the rate from continuing to decline. 238

3 Decelerating Safely Activity 25 Response to Student Sheet 25.2, Three-Level Reading Guide: Decelerating Safely 1. Check the statements below that you think say what the reading says. Sometimes the exact words found in the reading are used. At other times, other words may be used to communicate the same meaning. X a. When a car stops suddenly, the passengers inertia keeps them moving until they hit something. b. Air bags increase the pressure on the body during an accident. X c. A crumple zone helps passengers avoid harmful forces during an accident. 2. Check the statements below that you think represent the intended meaning of the reading. a. Brakes work by decreasing the friction between the brake pads and the wheels. X b. Controlling the deceleration of the passengers helps reduce injuries in an accident. c. Air bags help passengers concentrate the impact on one small area of the forehead instead of spreading it out over the head, neck, and shoulders. 3. Check the statements below that you agree with, and be ready to support your choices with ideas from the reading and from your own knowledge. a. Safety features have not improved much over the years. Students who agree with this may feel that the engineering developments have not been sufficient because people are still injured or killed in accidents. Those who disagree may feel that modern cars have improved to the point that poor driving is the only remaining safety problem. b. Tires are the most important safety item. Students who agree with this statement may point out that avoiding an accident is the best way to reduce injuries. Good tires increase friction and reduce stopping distance. They also improve handling and maneuverability. Students who disagree with this statement are likely to feel that just having good tires is not enough and that no one feature is the most important. Others might feel another feature, such as air bags, has done more than tires to prevent injuries in accidents. c. Designing safe cars is more important than reducing driver distractions. Students who agree with this may feel that safety features should help even those distracted drivers because there is no way to ensure that all drivers drive perfectly. Also, safety features are needed to protect other people who are not at fault for the accident. Students who disagree are likely to think that reducing driver distractions is a critical part of making driving safer for everyone. 239

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5 Name Date Talking Drawing: Safety Features 1. Close your eyes and think about what a safe vehicle looks like. Now, open your eyes and draw what you imagined. Label any parts of the vehicle that have special features. 2. After reading Activity 25, Decelerating Safely use the back of this page to draw and label a new picture of what you imagine a safe vehicle looks like. 3. In the space below, tell what you changed in your before and after pictures The Regents of the University of California SEPUP Science Grade 8 Student Sheet

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7 Name Date Three-Level Reading Guide: Decelerating Safely 1. Check the statements below that you think agree with what the reading says. Sometimes, the exact words found in the reading are used. At other times, other words may be used to communicate the same meaning. a. When a car stops suddenly, the passengers keep moving until they hit something. b. Air bags increase the pressure on the body during an accident. c. A crumple zone helps passengers avoid harmful forces during an accident. 2. Check the statements below that you think represent the intended meaning of the reading. a. Brakes work by decreasing friction between the brake pads and the wheels. b. Controlling the deceleration of the passengers helps reduce injuries in an accident. c. Air bags help passengers concentrate the impact on one small area of the forehead instead of spreading it out over the head, neck, and shoulders The Regents of the University of California 3. Check the statements below that you agree with, and be ready to support your choices with ideas from the reading and from your own knowledge and beliefs. a. Safety features have not improved much over the years. b. Tires are the most important safety item. c. Designing safe cars is more important than reducing driver distractions. SEPUP Science Grade 8 Student Sheet