The Importance of the Seatbelt

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The Importance of the Seatbelt
Laura Leidig
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It is a law in Pennsylvania that
All drivers and front seat passengers in
automobiles, light trucks and motor homes must
wear seat belts. If you are transporting
passengers age eight (8) or older but less than
age 18, they must wear seat belts, no matter
where they are riding in the vehicle. If you
are a driver under the age of 18, the number of
passengers may not exceed the number of seat
belts inthe vehicle.
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What is the importance of a Seatbelt?

• Many people believe they would be able to use
  their arms and legs to stop themselves from
  hitting the car's surfaces in a crash.
• In most crashes, the bodies of the passengers and
  drivers hit the car's interior surfaces with
  several tons of force, which would shatter even
  the strongest arms and legs.
• Only seat belts can safely slow your body.
• This chart shows that even though there are more
  people on PA Highways using their seatbelts, the
  more of deaths on the highway are victims that
  did not use their seatbelt.

Source http//www.psp.state.pa.us/troopp/cwp/vie
w.asp?A568Q171888
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Without a Seatbelt

• Consider the following example
• A car approaches a tree at 30 m/sec. What force
  is needed to stop the 60 kg driver in 0.1 sec?
• Since this is not a closed system, we use the
  equation Ft mvf mvi where
• F Force t time m mass v velocity (final
  or initial)

Ft mvf - mvi F (0.1s) 60kg (0 m/s) - 60 kg
(30 m/s) F (0.1s) - 1800Ns therefore F
-18000 N That force will be exerted on the
driver by the windshield, steering wheel, or the
tree.
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With a Seatbelt!

• The task of the seatbelt is to stop you with the
  car so that your stopping time is probably 4 or 5
  times greater than if you had no seatbelt.
• What is the difference in Force that would be
  exerted on the body?

A car approaches a tree at 30 m/sec. What force
is needed to stop the 60 kg driver in 0.5 sec?
(rather than 0.1 sec in the last example)
Ft mvf - mvi F (0.5s) 60kg (0 m/s) - 60 kg
(30 m/s) F (0.5s) - 1800Ns therefore F
-3600 N - Likely to be exerted across the
person's torso, which can cause injury, but not
as life threatening.
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Seat belts slow your body down far more gently
than a hard instrument panel, steering wheel or
windshield does. During a crash, fastened seat
belts distribute the forces of rapid deceleration
over larger and stronger parts of your body such
as the chest, hips and shoulders. Air bags
provide an even greater "ride down" benefit
however, even with an air bag present, a seat
belt must be worn.
Source PA Drivers Manual
Source PA Drivers Manual
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Seat belts also keep you inside of your car. Your
chances of being killed are almost 25 times
greater if you're thrown from your car. The
forces in a collision can be great enough to
fling you as much as 150 feet (about 15 car
lengths). Four (4) out of every five (5) people
who were killed by being thrown clear would have
lived, if they had been able to stay inside the
car.
Source PA Drivers Manual
Source PA Drivers Manual
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Always Buckle Up and Drive Safely!!