### E83

```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
– 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:
– 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:
– 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
– Wet roads are slippery. At 40 MPH on a slippery
car. Under these conditions my car would hit the
tree.
E83 Coming to a Stop
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
– EXPANDED ANSWER TO THIS QUESTION DUE
MONDAY
E83 Coming to a Stop
• 7. Create a concept map using the following
terms:
– reaction distance, brakes, distance
– 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.
```