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.