Do Now for 5/21/13 Take out E83 #6 and get ready to hand in Study for quiz HW: Anything not completed in class. E84 will be checked tomorrow E85 Crash Testing • Today’s Target: I will be able to design a crash test dummy that will give accurate feedback about what happens in an accident. • Quiz E81 through 84 • Write up E85 • Complete steps 1 through 3 • Analysis #1 • HW: Anything not completed in class E85 Crash Testing • You may discuss and share ideas with your partners BUT EACH PERSON MUST SUBMIT THEIR OWN DRAWING AND INFORMATION • Steps 1 and 4 combined – Answer each question on the back of your drawing. – MAKE SURE YOU INCLUDE SCIENTIFIC REASONING FOR ALL YOU ANSWERS. • Step 2 – Make sure you have a clear drawing – SHOW EFFFORT. • Step 3 – Mark the locations of all sensors on your drawing with an X. At least 5 sensors must be shown on your dummy. • Complete analysis #1. E85 Crash Testing • 1. The crash-test dummy that is most often used in frontal crash tests is the Hybrid III dummy. It is 5 feet 9 inches tall, weighs 170 pounds (the size of an average man), and costs about $100,000. What are the advantages and disadvantages of using the Hybrid III in all vehicle-crash tests? – The advantage of using the weight and height of an “average person” is that it represents the most common features of a vehicle occupant. It provides a standard for testing, which means the results of various tests can be compared. Another advantage is that is the most economical way to test vehicles that makes the final price of a car the lowest possible. The disadvantage is that height and weight of people vary, so the results are not accurate for much of the population. Students might suggest that crash tests should be done with dummies of at least two different sizes, an adult and a child, for example, which would provide more data. This would have the disadvantage of adding cost while still not gathering data on many other body sizes. E85 Crash Testing – Key Points • 1. When designing a solution or product, students must consider constraints—such as cost, time, trade-offs, and materials needed—and communicate ideas with drawings and simple models. • 2. Engineers often build in systems that provide safety. • 3. Technology influences society through its products and processes. It influences quality of life and ways people act and interact. Do Now for 5/22/13 • Take out E85 and get it ready to hand in. • HW: None E86 Investigating Center of Mass • Today’s target: I will be able to state how the center of mass affects what happens in a collision • Collect E85 • Check E84 • Introduce E86 • Gather data E84 Lab Check • Write up – 5 points • Analysis Questions – 5 points each = 15 points total • Key Points – 15 points • Total = 35 points E86 Investigating Center of Mass • Center of mass -sometimes called the center of gravity, is the point at the center of an object’s distribution of mass. • It is also the point around which the object balances. This is true even when two or more objects are working together in a system, such as the eraser on the end of the meter stick that is shown in the Student Book. • While mass is the total amount of matter or “stuff” in an object. • The center of mass describes the location around which the mass is equally distributed. E86 Investigating Center of Mass • Has anyone ever heard of a rollover accident? • Rollovers are common in single-vehicle accidents that occur when a vehicle swerves, hits a relatively immobile barrier, such as a guardrail, or becomes unbalanced when it goes around a sharp curve. • Although rollover accidents make up only about 3% of accidents, they account for 33% of accident fatalities. • Rollovers have the highest fatality rate of any type of accident. • Both the vehicle’s mass and center of mass determine how likely a vehicle is to roll over. Center of mass – mass evenly distributed around this point E86 Investigating Center of Mass • • • • Open book s to page E-58 Read background and write up. Draw data table Gather data Low C=center of mass vs. higher center of mass Low center of mass vs. high center of mass Do Now for 5/23/13 • Take out E86 data • HW: Test Wednesday E81 through 87 • Today’s target: I will be able to state which types of cars are more dangerous than others. • Review data for E86 • Analysis • Key Points • Begin E87 Sample Data E86 Investigating Center of Mass • 1. How did you rank the stability of the carts that had three different centers of mass? Describe the observations that determined your rankings. – Typically the empty, lower-center-of-mass cart is the most stable with the loaded, low center of mass cart in the middle. The observations that support this ranking are the frequency of rolling and the height that the wheels lift off the track. E86 Investigating Center of Mass • 2. How did a higher center of mass affect the cart’s motion after it hit the barrier? – When the cart hits the barrier, a force is applied to the lower part of the car, causing it to decelerate. The inertia of the part of the cart’s mass that is above the barrier causes it to continue to move forward due to its inertia. When the center of mass is higher, more of the car’s mass, and its associated inertia, are above the top of the barrier, making the cart more likely to roll off the track when the lower part is decelerated by the barrier. E86 Investigating Center of Mass • 4. Your friend's parents want to haul some lumber in their station wagon. His parents are not sure whether to put the lumber in the wagon or tie it on the roof rack. What advice do you give them? Explain in terms of center of mass. – Students should advise their friend’s parents to put the wood in the wagon because it would provide for a lower center of mass of the vehicle than if it were tied to the roof. The lower center of mass is safer because it makes the wagon more stable. E86 Investigating Center of Mass • 5. Why do think pickups and SUVs tend to roll over more often than passenger cars of similar mass? Explain in terms of center of mass. – Because of their higher ground clearance and overall profile, SUVs have a higher center of mass than passenger cars. This makes it easier for the center of mass to move outside of the wheelbase and cause the vehicle to roll over. E86 Investigating Center of Mass – Key Points • 1. An object that is not being subjected to a force will continue to move at a constant speed in a straight line. • 2. Scientific explanations emphasize evidence, have logically consistent arguments, and use scientific principles, models, and theories. Do Now for 5/24/13 • Take out sheet 87.1 • HW: Test on Thursday E87 Fatal Accidents • Read Background (page E-62) • Write up E87 – How does a cars design affect its’ safety? • Take out sheet 87.1 • Complete procedure • What kind of vehicle do you think has the highest and lowest risk of being in a fatal accident? • What kinds of accident do you think have the highest and lowest risk of fatalities? • Risk is the chance that a particular action or event could result in something unfavorable, such as injury or death. – Doesn’t mean that it will happen You will be using actual accident statistics to compare different types of vehicles in different kinds accidents. Vehicles are grouped according to mass and vehicle type. – Very small 4-door cars (2,100 lbs) – Mid-sized 4-door cars (3,000 lbs) – Toyota Tercel – Small 4-door cars (2,400 lbs) • Honda Accord – Large 4-door cars (3,600 lbs) – Honda Civic – Chevy Caprice – Large pickup trucks (4,500 lbs) • Ford F150 – Mid-sized 4-door SUVs (4,000 lbs) – Large 4-door SUVs (5,100 lbs) • Cadillac Escalade – Minivans (3,900 lbs) • Honda Odyssey • Ford Explorer • Go through the procedure and complete student sheet 87.1 • Complete analysis 1 through 4 • 1. How can the following aspects of a car's design help avoid accidents? • a. mass and inertia? – Lower-mass vehicles are often easier to maneuver to avoid an accident. For example, a small 4-door car is relatively easy to maneuver compared to a large SUV. A car with a lower mass may be less likely to roll or flip when the driver is trying to avoid an accident. • b. center of mass? – Cars with lower centers of mass roll over less easily than those with higher centers of mass. • c. braking distance? – Cars with a shorter stopping distance can stop before an accident. • 2. Use the data from the tables to explain which vehicle type is: • a. most likely to be in an accident that includes fatalities? – Very small 4-door cars are most likely to have a fatality in an accident because they have had more fatalities (20.6/BVM) than any other type. • b. least likely to be in an accident that includes fatalities? – Large 4-door cars are least likely to have a fatality in an accident because they have had fewer fatalities (9.3/BVM) than any other type. • 3. Use the data from the tables to explain which vehicle type in a two-car accident is most likely to cause a death of: • a. people in the other vehicle. – A large pick-up truck is most likely to cause a death in the other vehicle because it has the highest fatality rate (4.9/BVM) in two-car collisions. • b. its own occupants. – A very small 4-door car is most likely to cause a death among its own occupants because it has the highest fatality rate (7.1/BVM) in two-car collisions. • 4. Use evidence from this and other activities in this unit to explain why mid-sized cars and SUVs have: • a. different rollover fatality rates. – Mid-sized cars have a rollover fatality rate of 0.8/BVM, less than one-fifth that of the midsized SUV rate of 4.4/BVM. This is most likely caused by the SUV’s higher center of mass, which makes them more likely to roll over. • b. The same fixed-object fatality rates. – Mid-sized cars and SUVs both have a fixed object fatality rate of 2.6/BVM. This is most likely because they have a similar mass and inertia. The force of the crash is likely to have about the same deceleration in both vehicles. They also have similar interior size, which gives them a similar risk to injury caused by intrusion into the cabin space. E87 Key Points • 1. Risk analysis considers the type of hazard and the number of people likely to suffer its consequences. • 2. Students should provide causes for effects and establish relationships based on evidence and logical argument. • 3. Mathematics is important in all aspects of scientific inquiry.