Activity 84

Decelerating Safely

Challenge: How can a person’s deceleration be controlled

during a collision?

Getting Started…

• As a passenger, how do you know if you are accelerating while traveling in a car?

• How do you know when you are decelerating while traveling in a car?

• Let’s read the introduction on page 49.

• Complete the first part of the student sheet 49.1 “Talking Drawing: Safety Features”

• Complete the reading on pages 50-54. As you read, please complete the SS 84.2 “Three-level Reading Guide: Decelerating Safety”

• When you are finished, please answer Analysis Questions 1-4

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Analysis Questions:

1. Answers will vary.

On Impact, the car decelerates very rapidly, but inertia keeps objects within the car, including people, moving at a higher speed.

You should be able to explain how your safety feature helps to decelerate the body more gradually, so that there is an increase in time and a reduction in force.

2. If I had to choose between hitting a haystack or a telephone pole, I would chose the haystack. The collision with the more rigid and firmly attached telephone pole would cause the car to decelerate much more rapidly and produce a much greater impact force. The area of impact for the haystack is much larger than a telephone pole so the force of the haystack is decreased because it is distributed over a larger area.

3. Tires are designed to optimize the friction between them and the road so that the car gets good traction, handles well, and can stop quickly. As tires wear down, their ability to do all these safety related things decreases and the braking distance increases.

4. The fatality rate has been about the same for the past 20 years because major safety features that have occurred.

There are more distractions on the road today though that help to cancel out a lot of these safety features.

Weather and other factors will also prevent the rate from continuing to decline.