Do Now for 5/16/13 Take out E83 #3 and get it ready to hand in. HW: Analysis #6 due MONDAY E83 Coming to a Stop • Today’s Target: I will be able to state how different driving conditions affect stopping distance. • Collect #3 • Complete calculations • Graph data • Analysis 1 through 7 E83 Coming to a Stop • 1. Why does stopping distance depend on • road conditions? – Friction is what causes a car to stop. Road conditions affect the amount of friction between the tires and the road. Surfaces with less friction are, by definition, more slippery. E83 Coming to a Stop • 2. What might cause: • a. slippery road conditions? – Such things as snow, ice, gravel, and oil can cause slippery conditions. • b. driver distractions? – Such things as cell phones, music, passengers, eating, drinking, and other vehicles can distract the driver. E83 Coming to a Stop • 3. In which of the three situations (alert and dry, alert and slippery, or distracted and dry) does it take: • a. the least distance to stop? Explain using evidence. – At every speed, the stopping distance for “alert and dry” was less than either of the other sets of conditions. This can be seen by comparing the distances in the table or by the fact that the graph for these conditions was always below the other two graphs. E83 Coming to a Stop • b. the most distance to stop? Explain using evidence. – This depends on driving speed. At speeds of 9 m/s or less, the stopping distance for “distracted and dry” is more than either of the other sets of conditions. At speeds greater than 9 m/s, the stopping distance for “alert and slippery” is more than either of the other sets of conditions. This can be seen by comparing the distances in the table or by the fact that the graphed lines for “distracted and dry” and “alert and slippery” cross each other (at a speed of about 12 m/s) and are always above the line for “alert and dry.” E83 Coming to a Stop • 4. You are alertly driving a car at 40MPH (18 m/s). You come around a bend and see that a tree has fallen across the road 50 meters away. Will you be able to stop before you hit the tree: • a. on a dry road? Show your evidence. – At 40 MPH, it takes 46 meters for an alert driver to stop a car on dry pavement. Under these conditions my car would stop 4 meters from the tree. E83 Coming to a Stop • b. on a wet road? Show your evidence. – Wet roads are slippery. At 40 MPH on a slippery road, it takes an alert driver 81 meters to stop a car. Under these conditions my car would hit the tree. E83 Coming to a Stop • 5. Would your answers to Analysis Question 4 change if: • a. something were distracting your attention as you came around the bend? Explain. – If I were distracted, it would take 73 meters to stop in dry conditions. and I would hit the tree. In wet conditions I would hit the tree at a higher speed than if I were not distracted. • b. you were driving 20 MPH instead of 40 MPH? • Explain. – If I were driving 20 MPH, it would take 18 m to stop on a dry road and 27 m to stop on a slippery road. I wouldn’t hit the tree in either dry or wet conditions. E83 Coming to a Stop • 6. Your friend says that when a car goes twice as fast, its braking distance doubles. Do you agree or disagree? Use evidence from this investigation to support your ideas. – EXPANDED ANSWER TO THIS QUESTION DUE MONDAY E83 Coming to a Stop • 7. Create a concept map using the following terms: – stopping distance, tires, alertness – reaction distance, brakes, distance – road surface, speed, distraction – Braking, distance, time, friction E83 Coming to a Stop E83 Coming to a Stop – Key Points • 1. Friction is a force that will cause changes in the speed of an object’s motion. • 2. Important personal and social decisions are made based on perceptions of benefits and risk. • 3. The potential for accidents and the existence of hazards impose the need for injury prevention. • 4. Mathematics is important in all aspects of scientific inquiry.