Do Now for 5/21/13

Take out E83 #6 and get ready to hand inStudy 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.

E86 Investigating Center of Mass

• Open book s to page E-58• Read background and write up.• Draw data table• Gather data

Center of mass – mass evenly distributed around this point

Low C=center of mass vs. higher center of mass

Low center of mass vs. high center of mass

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.