Physics of Car Collisions

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Physics of Car Collisions
Brittany Foreman
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Types of Collisions - Inelastic

• An inelastic collision occurs when two objects
  collide and do not bounce away from each other.
• Momentum is conserved.
• Kinetic energy is not conserved. Some of it is
  turned into other forms of energy such as sound
  and heat.

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Types of Collisions - Elastic

• An elastic collision occurs when two objects
  collide and bounce apart.
• Both momentum and kinetic energy are conserved.
• Almost no energy is lost to sound, heat, or
  deformation.

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Impulse

• Impulse is the term to represent the force over a
  certain amount of time.
• In reference to car accidents, decelerating
  itself is not harmful it is sudden decelerating
  over a very short period of time that causes
  damage.
• F?t mvf mvi ? Impulse Equation

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Impulse (continued)
This graph represents a situation where a person
collides with the steering wheel or dash. All
force is transmitted within a fraction of a
second.
This graph represents the use of a restraining
device such as a seat belt or airbag. It spreads
the impulse out over a longer period of time.
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Severity Index

• Gives an idea of the chance a passenger has of
  survival in a collision.
• Takes into account both the magnitude of
  acceleration and the length of time during which
  it is experienced.
• S.I. (a5/2) t, where alpha is the acceleration
  in g, and t is the time of exposure in seconds.
• A proposed specification is S.I. 1000 for the
  human head.

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Examples of Severity Index

• Person falling back in a chair 1
• Throwing a baseball at 40 km/hr against a wall
  10,000
• Hammer hitting a nail in wood 3,000
• Hammer hitting a concrete wall 3,600,000
• Driving into concrete wall at 90 km/hr 24,000

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Newton

• Law of Inertia (1st Law of Motion) - An object at
  rest, or in uniform straight line motion, will
  remain at rest, or in uniform straight line
  motion, unless acted upon by a net external
  force.
• In reference to car collisions, this law deals
  with whether or not the person is wearing a seat
  belt. If not, the person continues forward to hit
  the steering wheel, to hit the dash, or to be
  evicted from the vehicle.

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Newton

• 2nd Law of Motion - A net force acting on a body
  produces an acceleration that is directly
  proportional to the force upon the body and
  inversely proportional to the mass of the body.
  (Fma)
• In reference to car collisions, this law deals
  with the force of impact a car and its riders
  exert on another car or object.

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Newton

• 3rd Law of Motion For every action there is an
  equal and opposite reaction.
• In reference to car collisions, this law deals
  with the collision itself. If the car hits a wall
  with a certain force, that force will be exerted
  onto the car by the wall, as well.

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THE END

• Would you rather crack a rib
• or your
  skull?
• WEAR A SEAT BELT!!