• Stopping distance

• Reaction distance

• Braking distance

• Condition of driver

• Vehicle equipment

• Car speed

• Road conditions

In your warm-up sectionMake a concept map using the

following terms:• Alert• Tires• defroster• Slippery• Dry• Under the influence of drugs or

alcohol• Windshield wipers• Brakes• Age• Mirrors• Headlights• distracted

Stopping Distance

depends on

Reaction distance Braking distanceand

is affected by is affected by

Condition of driver

Vehicle equipment

Road conditionsCar speed

Vehicle equipment

• alert• distracted• Under the

influence of drugs/alcohol

• age

• windshield wipers

• defroster• headlights• mirrors

• s = d t

• brakes• tires

• slippery• dry

Activity 82 Major Concepts• Friction is a force that will cause changes

in the speed of an object’s motion.

• The motion of an object can be described by its position, direction of motion, and speed.

Activity 83 Major Concepts• Condition of vehicle, driver and road all

affect the total stopping distance

• Initial speed x reaction time = reaction distance

• Weather conditions can affect the stopping distance

• Reaction distance + braking distance = stopping distance

Activity 83 Major Concepts

• Stopping distance is the sum of reaction time and braking distance

• There are many factors which affect stopping distance (list some)

• The potential for accidents and the existence of hazards impose the need for injury prevention

Activity 83 Analysis1. Why does stopping distance depend on

road conditions?

• friction

• road conditions affect friction

• surfaces with less friction are more slippery.

2. What might cause:

a. Slippery road conditions?

• snow, ice, gravel, and oil

b. driver distractions?• cell phone, music, passengers, eating, and other

vehicles3. 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.

• Explain using your evidenceb. the most distance to stop? Explain using

evidence.• This depends on driving speed. At speeds of

____ or less, ______________. At speed greater than ____, the stopping distance for....

4. You are alertly driving a car at 40 MPH (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 __meters for an alert driver to stop the car on dry pavement. Under these conditions my car would……

b. on a wet road? Show your evidence.

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 __ meters to stop in dry conditions, and……

b) You were driving 20 MPH instead of 40 MPH? Explain.

6. Your friend says that when a car goes twice as fast, its braking distance doubles. Do you agree or disagree? Use evidence from the investigation to support your ideas.

• My friend is wrong

• If speed doubles, the braking distance more than doubles (refer to your table)

• This is true for all speeds and conditions

• The graph also shows this because the shape of the lines are curved, not straight.

7. Create a concept map

Activity 84 Analysis1. Choose one of the safety features described in

the reading. Use the terms inertia, force, and deceleration to describe how the safety feature helps keep people safe in a collision.

• on impact, the car decelerates rapidly• inertia keeps objects within the car (including

people) moving at a higher speed• Describe how your chosen safety features

decelerates the body more gradually so that there is an increase in time and a reduction in force.

2. As a collision is about to happen, if you had enough time to chose between hitting a large haystack or a telephone pole, which one would you choose to hit? Explain why in terms of force and deceleration.

• The haystack• telephone pole is more rigid (and attached)

resulting in ____ impact force• area for impact of haystack is _____• force from haystack is decreased

because…..

3. In the accident mentioned in Activity 73, “Choosing a Safe Vehicle,” Noah’s family car had old tires that were worn down. Explain how this could have contributed to the car accident.

• Tires are designed to optimize friction between the tires and the road

• The car gets:

• good traction

• handles well

• can stop quickly

• describe what happens as tires wear down

4. Reflection: Since the 1920’s, the rate of fatalities per billion miles traveled has dropped steadily. However, the rate has been about the same for the past 20 years. Why do you think this is?

• Include ideas about:• major gains in safety features occurred

before/after the rate settled• more distraction on the road• minimum number of “bad” drivers will stop it from

dropping indefinitely• weather & other factors keep it from continuing

to decline

Some factors that tend to keep fatality rates the same are:

• more distractions, such as cell phones and handheld electronic devices

• a larger number of older drivers

• lack of seatbelt use (almost 40% of all passengers killed are not wearing seatbelts)

• reintroduction of higher speed limits

• less car uniformity (mass, bumper height) when vehicles collide

Activity 84 Major Concepts

• Airbags decrease force on the body during an accident

• Tires and brakes are the most important safety features in a car

• Rapid deceleration and hitting hard objects cause most injuries in accidents

Activity 84 Major Concepts• Technology influences society through its products

and processes. It influences quality of life and ways people act and interact.

• Some devices can decrease injuries and fatalities in more than one way. Seatbelts help reduce the collision force by increasing the area of the force across a person’s body, redirecting the force from the head to the broader torso, and by decelerating the body over more time than if it hit the steering wheel or dashboard.

Read E-58

Activity 86

Title: Investigating Center of Mass

Problem: How does the center of mass affect what happens in a collision?

Hypothesis: If _____, then __________.

In this activity you will investigate the similarities and differences between mass and center of mass in the context of car accidents.• Center of mass, sometimes called the

center of gravity, is the point at the center of an object’s (or system’s) distribution of mass. It is also the point around which the object balances

• 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.

• Determining the center of mass of irregularly shaped objects and objects made from a variety of materials, such as cars, can be difficult.

• Most often the center of mass is found inside the object, such as in the chassis of a car.

• The center of mass can be found outside its shape, such as in a boomerang that has a center of mass in between its two shaped arms.

Have you heard of a rollover accident?

• Common in single vehicle accidents when

-a vehicle swerves

-hits a relatively immobile barrier (such as a guardrail)

-becomes unbalanced when it goes around a sharp curve.

• Rollover accidents make up 3% of accidents, but account for 33% of accident fatalities. They have the highest fatality rate of any type of accident.

Read the procedure on pages E-59 to E-60

• The two loaded carts have the same mass.

• The relative position of the heavier metal cylinder determines the center of mass.

• Pay attention to procedure steps that require predictions (steps 6 and 9)! Write the step number and predictions below your table.

Observations & Stability Rating

• Did the rear wheels come off the ground? If so, how far?

• Did the wheels come off the track?

• Did the cart tip over?

• Stability Rating: Use 1-3

1 = most stable, 3 = least stable

Compare results before beginning analysis questions

• The results of the loaded-cart investigation can only be applied to the situation of a single car colliding with a fixed barrier.

• How might accidents on a real road be different?

Auto AccidentsSUV Rollover Accident Injury Lawsuits and Litigation

SUVs were originally designed as work vehicles and most are still built using a truck chassis. Never intended as passenger vehicles, SUVs feature a high profile and narrow track that makes them very rollover-prone. With their weak roofs and poor crash protections, SUVs roll over with enough frequency to account for sixty percent of the more than 10,000 rollover fatalities in the U.S. every year.