Activity 83

Coming to a Stop

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

Key Vocabulary

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

• Stopping Distance – the sum of the reaction time and the braking distance

Getting started…

• Imagine drawing down a road, and seeing a tree lying across the road.

• What factors do you think will affect whether you will be able to stop before you hit the tree?

• Car Speed, how far away the tree is, condition of the driver, vehicle equipment, and road conditions will contribute to whether or not you will hit the tree.

• Which of your stopping factors affect the reaction distance and which affect the braking distance?

• The driver is in direct control of 2 critical factors:– Car speed – Alertness

Doing the Activity…

• Read the Introduction on page 45

• Follow the Procedure Steps 1-3– Copy the equations for reaction

distance and stopping distance in your notebooks!

– Label your graphs correctly!

• When you are finished, answer analysis # 1-5.

Check

your

Resu

lts:

Analysis Questions

1. Stopping distance depends on road conditions because friction is what causes the car to stop. Road conditions affect the amount of friction between the road and the tires. Surfaces with less friction are, by definition, more slippery.

2. Snow, ice, gravel, and oil can cause slippery road conditions.

Such things as cell phones, music, passengers, eating, drinking, and other vehicles can distract the driver

3.

a. At every speed, the stopping distance for “alert and dry” was less than either of the other sets of conditions.

b. What can take the most distance to stop will depend on driving speed. Speeds less than 9 m/s or less the stopping distance for ‘distracted and dry” is more than either of the other sets of conditions. Speeds greater than 9 m/s , the stopping distance for “alert and slippery” is more than either of the other sets of conditions.

4.

a. 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.

b. Wet roads are slippery. At 40 MPH on a slippery road, it takes an alert driver 81 meter to stop a car. Under these conditions my car would hit the tree.

5.

a. 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. 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.