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Accident Reconstruction Glossary

Below you will find some glossary terms for Accident Reconstruction. We will be adding to this site from time-to-time.

Acceleration: a change in velocity with respect to time. Values are either positive or negative with standard orientation.

Acceleration Scuff: friction marks that occur when the tires on the drive wheels of the vehicle are turning faster than they would normally turn, given the speed of the vehicle.

Asphaltic Concrete: a flexible roadway surface that meets the needs of most highways. It is constructed of an asphalt and rock mixture and is black in appearance.

Brake Build-up (Brake Lag): occurs just after the brakes are applied and continues until they lock.

Chord: a straight line that intersects a circle at two (2) points.

Coefficient of Kinetic Friction: ratio of the magnitude of the force of kinetic friction to the magnitude of the normal force.

Collision Scrub: occurs during a traffic collision when the downward and rotating forces cause a smearing of tire material on the road surface.

Coordinate Method: technique of scene documentation where items of evidence are located by measuring the distance from two (2) reference lines. Similar in concept to locating points in the Cartesian plane.

Delineators: those devices that direct, channel and separate vehicular traffic.

Divided Attention: the ability or lack thereof to do more than one thing at the same time.

Effective Drag Factor: the ratio of the velocity squared to the quantity of the skidding distance multiplied by twice the gravitational constant.

Final Rest Position: controlled or uncontrolled post-collision resting position of vehicles, pedestrians, debris, etc.

Friction: the resistance of an object to movement across a surface.

Gaze Nystagmus: Involuntary oscillation of the eyes as they gaze at an object moving through the field of vision.

Impact Aspersion: occurs when a fluid container is ruptured under extreme pressures of impact and then aspersed onto the roadway.

Impending Skidmarks: also known as shadow skidmarks are small fragments of rubber, ground or scraped from the tire, at the tire and roadway interface, as the rotating tire slows to a locked position.

Kinematics: the branch of mechanics that uses mathematics to describe motion, without reference to the forces or masses involved.

Kinetic Friction: describes the frictional forces present between surfaces in relative motion.

Middle Ordinate: the distance of the center point of the chord, to the outer edge of the inertial scuffmark. Used in determining the radius of the circle that most closely approximates the shape of the arc.

Momentum: the mass of an object multiplied by its velocity. It is a vectored quantity with both magnitude and direction.

Normal Force: the force that a body exerts on another body at right angles to their mutual interface.

Pedestrian Manifestations: those items of evidence deposited at the collision scene by the pedestrian during or following impact.

Point of No Escape (by braking): consists of te perception/reaction distance plus te slide-to-stop distance for the specified velocity.

Portland Cement Concrete: a rigid roadway surface designed for roadways that are continuously exposed to large trucks, large volumes of traffic and sections of roadway where the grade is 12 percent or greater. The color is normally white or grey.

Raised Pavement Markers (R.P.M.): Non-reflectorized ceramic pavement markers, also known as "Bott's Dotts", are most often used to delineate travel lane lines. Reflectorized RPM's come in many different colors and are used to delineate travel lane lines and outside boundaries.

Safe Stopping Distance: same value as the point of no escape.

Scientific Method: 1.) make observations of available facts; 2.) develop a hypothesis; and 3.) test the hypothesis

Scuffmarks: friction marks left on the roadway by tires that are free to rotate.

Skidmarks: dark deposits of tire and roadway material normally deposited on a roadway surface by a tire that is not free to rotate.

Speed: magnitude void of direction.

Soradic Trickle: the fluid trail that usually starts after impact aspersion and continues to the vehicles final rest position or until the fluid container is empty.

Static Friction: describes the frictional forces present that are between surfaces at rest with each other.

Triangulation: technique for scene documentation where items of evidence are located by measuring the distance between two (2) reference points.

Velocity: a change in position with respect to time. Has properties of both magnitude and direction.

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