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Sir Isaac and Seat Belts

    Eric Clapton's Tears in Heaven was written in memory of his young son who died in an accidental fall from a multistory hotel window. In a tragic instant, his son climbed out the window with the speed and quietness so characteristic of inquisitive toddlers. Genuine and heartfelt sympathy came from parents all over the world, and I suspect many readers sadly remember the incident. A parent's worst fear is losing a child.
    For obvious reasons, I've not met a parent who would be willing to jump out of a seventh-story window or allow his or her children to play on the outside ledge of such a window. We would question the judgment, if not the sanity, of anyone capable of such an act. Yet forty percent of Colorado's parents expose themselves and their children to a surprisingly similar risk every day--they fail to use seat belts when riding in an automobile.
    If you are a die-hard (no pun intended) anti-seat belt person I support your freedom of choice (although you should make yourself aware of the seat belt laws). But with freedom comes the responsibility to make informed, intelligent choices. Read on with an open mind. If you are a casual user of seat belts, perhaps you will be motivated to make seat belt use a consistent habit. If you are a full-time user, you might appreciate some scientific affirmation of your choice.

The Statistics

    A single story often makes more of an impression on us than a statistical number (hence the beginning of this essay). Yet good, reliable statistics represent thousands of stories, and show us the common themes among them. Seat belt statistics are based on studies of thousands of accidents--real tragedies--from recent years. From the Colorado and US Departments of Transportation, here they are:
  • traffic crashes are the leading cause of death for Coloradans age 5 to 25
  • one out of three people will be seriously injured in a car crash during their lives
  • nationwide, two-thirds of auto occupants wear seat belts
  • nationwide, two-thirds of those killed in auto crashes were not wearing seat belts
  • seat belt users are nearly twice as likely to survive a serious crash as non-users

The Science of Seat Belts 
    Sir Isaac Newton (1642 -1727) was one of the most influential scientists to have ever lived. His many accomplishments included proposing the theory of gravity and developing the three laws of motion. Newton, of course, never saw an automobile. Yet through his laws of motion he would have been able to clearly predict and explain the need for seat belts.
      Newton's first law of motion simply states that any moving object will keep moving at the same speed and direction until some force causes the object to change its motion. When you first get in a car, a force is required to change your motion. As you accelerate the car, you feel the back of the seat pushing you forward. As soon as you reach a constant speed, though, you no longer feel the seat pushing you from behind. Your body will continue to move in the same speed and direction until a force causes the motion to change.
    If a car is traveling at 45 mph and hits a stationary object, the car will stop but the occupants will continue moving in the same direction at 45 mph. Unbelted passengers will then smash into the dash at that speed, or worse, travel through the windshield until hitting another object (tree, car, pavement). Belted passengers, though, will be caught by the seat belt, avoiding a collision with the dash or windshield.

Sobering Comparisons
Colorado ranks below the national average in seat belt use, with rural areas having the lowest belt use rate. Perhaps the reason why so many of us don't wear seat belts is because we just don't think about the forces involved in crashes. Here are some examples to consider.

Dashboard on a Bumper
    Imagine a car with a dashboard mounted on the front bumper facing away from the car traveling down a road at 45 mph. Would you be willing to stand in front of it? Of course not, but the collision is no different than crashing your own car into a stationary object at 45 mph without a seat belt fastened. Whether you hit the dash or the dash hits you, the results are the same.

A Seven-Story Fall
    Two seconds after falling out of a seventh-story window a person would hit the ground at a speed of 45 mph. The bodily impact would be essentially the same as the 45 mph unbelted crash mentioned above. None of us would intentionally let our children out on a high window ledge. Yet, in Colorado, forty percent of us don't buckle up our kids (or selves).

Throwing Your Arm Out
    Many parents mistakenly believe they can restrain an unbelted child in a sudden stop simply by throwing their arm in front of the child. Newton's second law explains why this won't work. Newton discovered that the faster an object moves, the greater the force required to change its motion. Stopping an unbelted 50 lb child in a 45 mph crash by throwing an arm in front of the child would be like trying to stop a 1000 lb steer from trotting past you at 10 mph with an extended arm. Both feats require the same amount of energy!

Infant in the Lap
    One of the most dangerous places for an infant to ride in a car is in the lap of an unbelted mother. In a crash, the infant has little chance for survival. Imagine a 120 lb woman holding a baby in her lap in a car that crashes into a stationary object at a mere 30 mph. When the car stops, the baby and mother keep traveling forward at 30 mph. The baby smashes into the dashboard at that speed but the worse is yet to come. At 30 mph, the mother then smashes the baby into the dashboard from behind with a force of over 1,200 lbs! Even if the mother is belted in, she will not be strong enough to hold the baby in her arms. In a 30 mph crash, a twenty pound infant will pull away with a force of over 200 pounds.

Seat Belt Myths
    Most people probably know they should wear seat belts but many don't think about it enough to form the habit. Still, some people are convinced they are better off not wearing belts. Here are some of the myths commonly cited by those who intentionally don't buckle up:

-It's better to be thrown clear. In fatal crashes, one in four unbelted occupants are ejected. Of  those ejected, three out of four are killed. An ejected occupant flies head first through the windshield and into an oncoming car, a tree, pavement, or some other object.

-Seat belts trap you in a burning car or underwater.
Nearly every crash in the movies or on television involves an exploding car or a crash in water. The reality is that less than one percent of all crashes involve either fire or water.  In the unlikely event of such a crash, though, belted occupants are much more likely to be uninjured and coherent enough to release themselves.

-Seat belts are only needed on the Interstate.
Most crash deaths occur within 25 miles of home at speeds under 40 mph. Seat belts should be used on every trip, no matter how short.

-My shoulder harness won't hold me.
A built-in convenience device on newer vehicles allows for freedom of movement under normal driving conditions but locks the belt in place during any sudden change of motion. Some people mistakenly believe their belts don't work properly because of the added freedom of movement.

-Seat belts cause injuries in a crash.
During a serious crash, seat belts might cause some bruising. However, the injuries caused by not wearing a seat belt are much worse.

Make it Click
    Car crashes are terrible events that involve incredible forces. The human body is delicate and fragile. Seat belt use will not ensure survival of every accident. But it is important to understand the forces involved in a crash and realize the effectiveness of seat belts in preventing or reducing injury. Always buckle up. Sir Isaac Newton certainly would have.

2006  Dirk Oden





This site was last updated 09/04/06