Topics include Newton s laws, pressure, work, average velocity, kinetic energy, momentum and conservation of momentum, work-energy theorem

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1 Chapter 3: Safety Overall: Topics include Newton s laws, pressure, work, average velocity, kinetic energy, momentum and conservation of momentum, work-energy theorem Sections 1-2: These two sections introduce safety and safety features in automobiles. Section 1 can be skipped over or the quiz be used as a short introduction to safety. Very little time needs to be spent on the first section and can easily be combined with section 2. The investigation in section 2 has students sending a clay model down a ramp without seatbelts, then with narrow and then wide seatbelts. This introduces the idea of pressure and reinforces Newton s 1 st law. Section 3: Students use eggs and flower to understand how stopping distance changes the amount of force an object experiences. This is a high-interest lab that introduces Kinetic Energy and the work-energy theorem and reinforces Newton s second law. Section 4: This section deals with Newton s 1 st and 2 nd law in a new way. Even though our kids have a lot of exposure to Newton s laws at this point they typically are unable to hypothesize motion in a rear end collision. This is a valuable and fun lab. - 5 Section 6 Section 7 Must-Dos: Scientific Practices: It is important to recognize that scientific practices are a key part of the investigative process in this book even though they are not always specifically drawn out in a manner you may be used to. Your students will be responsible for understanding experimental design and must be able to create hypotheses, identify variables and constants, interpret qualitative and quantitative data, and make conclusions that justify what has been learned. Ensure that your instruction explicitly focuses on these practices in all the sections you teach. You can expect that district and state assessments will contain questions relating to scientific practices Learning Outcomes, Pitfalls, Misconceptions by Section Section 1: Accidents pitfalls: Identify and evaluate safety features in selected automobiles Compare and contrast safety features in selected automobiles Identify safety features for other modes of transportation (in-line skates, skateboards, motorcycles) Very little time needs to be spent on this section. Have the students take the quiz as a warm up in class and spend a few minutes discussing each question. Make copies of the table for the students to save time. misconceptions:

2 After reading the Physics Talk, students seem to think that having a solid steering column is a safety feature. The quiz can be passed over in section Section 2: Safety and Seatbelts Explain Newton s first law of motion Identify the three collisions in every accident Compare the effectiveness of various wide and narrow seat belts Express the relationship between pressure, force, and area pitfalls: Have a student assistant make the clay models ahead of time. Some modeling clay is too hard and significant injury might not be visible. Play Dough is an option but it will dry out over time. Also, the wire may make an indentation in the model that is difficult to remove, making students think that all seatbelts cause the same amount of damage. misconceptions: This section discusses pressure and designing a safer seatbelt. Emphasize that the force each seat belt exerted to stop the passenger was the same, but the results were different. To help students differentiate force from pressure, have the students stand on two feet, then one, then their toes. Correlate pressure they felt with the amount of contact. The force remained constant but as area decreased pressure increased. Section 3: Why Air Bags? Model an airbag Relate the energy of a moving object to the work required to stop the object Demonstrate an understanding about the relationship between the force of an impact and the stopping distance The flour in this lab can be messy. Have the students use a Petri dish and a ruler to get the flour level, then place the Petri dish into a container. Some teachers have had eggs taken from the class. Account for each group s eggs at the end of the activity.

3 Misconceptions: Students think that stopping distance is decreased when an airbag deploys because they confuse traveling distance and stopping distance. Emphasize that an airbag increases the distance over which a person s head stops compared to a dashboard, even though the distance the person s head travels through the air prior to hitting an object is less when an airbag deploys (fix the phrasing on this). The egg hitting the sheet is a good example to return to when discussing stopping distance. Some students confuse work with force. Remind students that the amount of work done on both eggs was the same, since the total work done on an object is equal to the change in its kinetic energy. Both eggs had the same KE since they were dropped from the same height. Students struggle with the idea that for a given force, the stopping distance is proportional to the speed squared. (d=v 2 /2a). If a vehicle triples its speed from 10 to 30 m/s, the stopping distance will be 9 times greater than before. Section 4: Newton s Second law of Motion: The Rear-End Collision Evaluate, from simulated collisions, the effect of rear-end collisions on the neck muscles Describe the causes of whiplash injuries Provide examples of Newton s first and second laws of motion in automobile crashes Analyze the role of safety devices in preventing whiplash injury Have a student assistant fold the templates (see the blackline masters) ahead of time and try them out on the carts to be sure they are the correct width. Make the clay figures ahead of time to save money. Students will struggle with seeing how much the neck bends in a rear end collision. Be sure to use wire that is strong enough to hold the head but is still able to bend. After each collision the wire needs to be straightened and the head re-fastened securely. Remind students of things that need to remain constant: target car beginning at same spot, resetting the wire between each trial, etc. Misconceptions: Students believe that a head moves backward in a rear end collision, when in fact it remains at rest and the rest of the body moves forward.

4 Below are some videos of older and newer cars involved in rear end collisions. These can be helpful when discussing the results of your investigation Have students take the whiplash quiz found in the Physics to Go together on whiteboards. Section 5: Momentum: Concentrating on Collisions Apply the definition of momentum Conduct analysis of the momentum of pairs of objects involved in onedimensional collisions. In order to see momentum being conserved, it is important to use carts with very little friction and also to emphasize to students to observe just before and just after the collision. Understand and apply the law of conservation of momentum to collisions. Measure the momentum before and after a moving mass strikes a stationary mass in a head-on collision Use tracks to make sure the collisions will occur at the center of the carts. Tape the weights into the carts. Tape an index card to the side of each cart so the velocimeter will more easily detect the motion of the carts before and after the collision. Make a copy of the data tables for the kids to save time. For the 6 collision types, provide a table with the Type of Collision, the Before sketch and the After sketch. Model how to fill in each column. Provide carts for the kids to use if they struggle with visualizing the collisions. When calculating momentum before and after, have students create a T-chart to separate each object s individual momentum. There will be a lot of variation on the data collected. Be sure to discuss sources of error, unbalanced forces from the environment, and difficulties in working with models.

5 Section 7: Impulse and Momentum: Crumple Zone Learning Outcomes: Design a device that is able to absorb the energy of a collision and reduce the net force on an object in an automobile. Describe collisions and crumple zones in terms of momentum, impulse, and force. Use a motion probe to determine the velocity of moving vehicles. Compare the change of momentum of a model vehicle before a collision with the impulse applied during a collision. Explore ways of using cushions to increase the time that a force acts during a primary collision. ***this section to be completed as the school year progresses*** Misconceptions: