The Physics of Car Safety

18 Dec 2011


When a car stops suddenly, you keep going. This example of Newtons ?rst law of motion has been responsible for many traf?c injuries. Countless drivers and passengers have survived horrible crashes because they were wearing seat belts, and air bags have also played a major role.
To understand the physics behind the design of air bags, imagine that the car you are driving is suddenly involved in a head-on collision. At the instant of impact, the car begins to decelerate. Your head and shoulders jerk forward, and the air bag pops out of its compartment. The bag must in?ate rapidly, before your head reaches the wheel, and then start to de?ate as your head hits it. This causes your head to decelerate at a slower rate. In addition, the force of your impact with the air bag is exerted over a wider area of your body, instead of being concentrated at the impact site of your head with something small, such as the top of the steering wheel.
Physics is also involved in the design of car tires. The key consideration is the amount of tire area that stays in contact with the road during braking and turning; the more tire contact, the better your control of the car. Also important is
having tires that resist hydroplaning on wet roads at slow speeds, water skiers sink; at high speeds, they glide over the surface of the water. Thats just what you do not want your car tires to do in the rain. Engineers used various physics principles to design tires with a centre groove that pumps water away from the surface as the tires roll over wet pavement.
1. Air bags have come under increased scrutiny. Research the reasons for this debate.
2. To keep more rubber in contact with the road, tires could be made wider. The ultimate would be a single tire as wide as

the car. What would be the disadvantage of this type of tire? What might limit the maximum width of a tire?

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