Crumple Zones and Air Bags

## Question:

How would you describe the function of crumple zones and/or airbags in terms
of Newtons' second law?
## Answer:

Suppose that you and your automobile are traveling at 2 meters per second
and hit a very large object like a concrete wall head on. Your speed will
be reduced to zero in the time it takes to complete the collision. If that
time is very short, say 10 milliseconds, the acceleration you experience
will be large, 2 mps / 0.01 seconds is 200 mps/second. According to
Newton's second law the force required to produce this acceleration is given
by f=m*a where m in your mass. If that is 50 kg then the force of the
collision on you is 50*200=10,000 Newtons. A force of that magnitude is
going to do you some serious damage.
A crumple zone increases the amount of time it takes the car to stop
relative to the immovable object and an air bag increases the amount of time
it takes you to stop relative to the car. Suppose that together they extend
the time for you to come to a stop from 0.01 seconds to 0.2 seconds.
Increasing the slowing down time by a factor of 20 reduces the acceleration
and therefore the force by the same factor, resulting in a force on you of
500 Newtons instead of 10,000. Still probably no fun, but likely to be
survivable.

This information is brought to you by M. Casco Associates, a company
dedicated to helping humankind reach the stars through understanding how the
universe works. My name is James D. Jones. If I can be of more help,
please let me know.

JDJ