HALL - CARPENTER, CO.

By Edwin T. Scallon, Copyright © 1990, 1995, 2008 All Rights Reserved

ACCIDENT RECONSTRUCTION AND BAC CALCULATION PROGRAMS

MOTOR VEHICLE FALLS

      A fall is a downward and outward movement in the air under the force of gravity after forward momentum carries an object beyond its supporting surface; rotation during a fall is gradual and the object usually lands righ side up.

    The definition of a fall is when the vehicle is no longer supported by the roadway surface underneath it. All bodies in free fall near the earth's surface have the same downward acceleration of 32.2 ft/sec/sec. A body in free fall has the same downward acceleration whether it starts from rest or has an initial velocity. The presence of air affects the motion of falling bodies partly through buoyancy and partly through air resistance. In vehicle reconstruction buoyancy and air resistance are negligible and can be neglected in the calculations. The formulas for straight-line motion can be used to analyze the horizontal and vertical aspects of a vehicle's flight. The horizontal velocity component remains constant during flight and the effect of gravity on the vertical velocity component is to provide a downward acceleration. The formula for calculating the velocity at the beginning of a simple fall is: Where :

                              V = d √g/2(dG-h)

                               v - velocity (fps)

                               d - horizontal distance traveled in the air (ft)

                               h - vertical distance, the difference in the elevation from take off to landing, an elevation higher at touchdown than at takeoff is (+) ( feet), and                                                    elevation lower at touchdown than at takeoff is (-) (feet),

                              G - grade of the traveled surface at take off Upgrade is positive and downgrade is negative, (ft/ft) g - acceleration of gravity, 32.2 ft/sec².

    The horizontal distance is the distance the center of mass traveled from an unsupported location to the point of first contact with ground measured horizontally. The final position of the vehicle may not be the point of first contact. Caution should be taken to ascertain the accurate location of first contact and not be misled by the final rest location of the vehicle. The vertical distance is the distance the center of mass traveled vertically from the unsupported location to the point of first contact. Again care should be exercised in determining the point of first contact and not assume that the final position of the vehicle is the point of landing

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