Blind Siding Physics

Much of this video focuses on the side of the movie that is more important to the viewer: character development.  However, at 1:09, something occurs that is much more interesting physics wise: a collision.  The truck in which Michael Oher and S. J. Tuohy are traveling  in has a good amount of momentum.  Momentum is how hard something is to stop, and is generally measured in kilograms*meters-per-second, or mass*velocity.  If we want to calculate this, we can assume the Michael’s Ford F-150 weighs about 5,000 pounds, or around 2,250 kilograms, and that he’s driving at around 40 miles per hour, or about 18 meters per second.  This means that the momentum the F-150 has is about 40,500 kg*m/s.  We further know that when the truck crashes into the bigger vehicle, it eventually comes to a complete stop.  Of course, when an object is at a standstill, its velocity is 0 m/s, so its momentum must also be 0 kg*m/s (any number multiplied by 0 is 0).  Therefore, we know the ultimate change of momentum is equal to the entire momentum that we calculated earlier, as it is going from that number to 0.  This change in momentum is called impulse.  Impulse also equals something else: force times a change in time.  Force is a unit measured in Newtons (the force required to accelerate a one kilogram object at one meter per second per second), and is any amount of push or pull that accelerates an object.  A greater force can be more harmful for a person because it can shatter bones and damage organs.  Therefore, soon after the collision in this video, one of the greatest innovations in automobile safety activates itself: the airbag.  This extends the time before the person in the car hits the harder surface of the car’s dashboard.  If the impulse stays the same, but the change in time increases, that means that the other value, force has to decrease.  This decreased force poses less of a danger to the person in the car than the original force.  Perhaps this is the reason S. J. survives the accident, though he is injured.


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