Read E-45

Activity 83Title: Coming to a Stop

Problem: How does a car’s stopping distance change in different situations?

Hypothesis: If _____________, then ______________________.

Imagine you are driving down aroad and see a tree lying across the road. What factors do you think affect whether you will be able tostop before you hit the tree?• 5 Categories

-Car Speed-Distance from the Tree-Condition of the driver-Vehicle Equipment-Road Conditions

Background Information:• Braking Distance is the distance it takes

for the car to stop once the brakes have been applied.

• Reaction Time is the time period between the driver’s realization that there is danger ahead and his or her engaging the brakes.

• Stopping Distance is the distance it takes a driver to stop a car. It is the sum of the reaction distance and the braking distance.

Background Information (continued):

Reaction distance = x

Stopping distance = +

initial speed

reaction time

reaction distance

braking distance

• Reaction Distance• Condition of Driver • Car Speed • Vehicle equipment

• Braking Distance• Car Speed• Road Conditions• Vehicle Equipment

The driver is in direct control of two critical factors—

car speed and alertness

Which of your “stopping factors” affect the reaction distance and which affect

braking distance?

Graphing

1. Give the graph a title2. Number the x-axis 5, 10, 15, 20----403. Number the y-axis 50, 100, 150-----3004. Use as much of the axis as possible5. Label axes, including units6. Color Code Key7. Plot Points8. Best Fit Curve (DO NOT CONNECT THE

DOTS WITH A STRAIGHT LINE!!!!)

Best Fit Curve

Activity 82 Analysis1. In this experiment:

a. What does the cloth model?The cloth models the brakes on a real vehicle.b. List some strengths and weaknesses of this model.

• Good model because it slows the vehicle• Not representative of real breaking system in a

car• The driver can apply a varied force, but the

cloth applies a constant friction.

2. What affect does speed have on the braking distance? Explain, using evidence from this activity.As initial speed was increased, the braking distance also increased. Use evidence from your activity to support this.Prior knowledge: what do you know about the various speed at each notch height?

3. Does the evidence you gathered in this investigation support the statement below?A car moving at 55 mph needs less distance to stop than an identical car moving at 45 mph.This statement is not supported by evidence gathered in this investigation. Use your evidence to explain.

4. Reflection: Why do you think speeding is a factor in a high percentage of car accidents?There are many reasons speed is involved in a high number of fatalities. This activity showed …… Evidence from Activity 76 showed……….

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 it position, direction of motion, and speed.