Do Now for 5/20/13 Take out E84 Report HW: Quiz on E81 through 84 tomorrow. E83#6 due tomorrow

E84 Decelerating Safely Today’s Target: I will be able to state how a human can decelerate safely in a crash. E83 Rubric – Due Tomorrow Review Concepts Analysis answers Quiz Review

E84 Decelerating Safely 1. 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 very rapidly, but inertia keeps objects within the car, including people, moving at a higher speed. You should be able to explain how your chosen safety feature helps decelerate the body more gradually, so that there is an increase in time and a reduction in force.

E84 Decelerating Safely 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. – Hitting a haystack would be more desirable because 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.

E84 Decelerating Safely 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 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.

E84 Decelerating Safely – Key Points 1. An object that is not being subjected to a force will continue to move at a constant speed in a straight line. 2. The magnitude of a change in motion can be calculated using the relationship F = ma, which is independent of the nature of the force. 3. The potential for accidents and the existence of hazards impose the need for injury prevention. 4. Engineers often build in systems that provide safety. 5. Technology influences society through its products and processes. It influences quality of life and ways people act and interact.

Quiz Review E81 through 84 Should be able to draw diagrams showing the net force. Is the object accelerating when the forces are balanced? Unbalanced?

Quiz Review E81 through 84 – F=ma You should know how to solve the equation. – Two identical cars travelling a different speeds, which one stops first. – Calculate reaction time and stopping distance. – How do safety features in a car reduce the forces a passenger experiences?