Physics of Movement and Collision

Physics of Movement and Collision

Understanding Motion Physics

  • Motion physics refer to the principles of mechanics that describe the motion of bodies.
  • A solid understanding of motion physics is central to the forensic analysis of traffic collisions.
  • Key concepts in motion physics include velocity, acceleration, and momentum.


  • Velocity refers to the speed of an object in a given direction.
  • Determining the velocity of a vehicle pre-collision is crucial, as it can reveal if speeding was a factor in the incident.
  • Velocity is often inferred from elements such as brake marks, vehicle debris, and eyewitness accounts.


  • Acceleration signifies a change in velocity; an object accelerates if its speed or direction changes.
  • Acceleration is typically distinguished by aspects like sudden tyre marks or vehicle damage indicating a sudden stop or swerve.


  • Momentum is the product of an object’s mass and velocity.
  • In a collision, momentum is transferred between the interacting bodies; understanding this gives insight into the collision’s force and direction.
  • Analysis of collision damage, tyre marks and final vehicle resting positions can help in approximating the momentum of the vehicles involved.

Understanding Collision Physics

  • Collision physics involve the principles that govern the interaction between bodies during a collision.
  • A comprehensive understanding of collision physics is invaluable when deciphering how a traffic collision occurred.

Elastic and Inelastic Collisions

  • Collisions can be classified as either elastic or inelastic based on the conservation of kinetic energy and momentum.
  • In an elastic collision, both kinetic energy and momentum are conserved - these are less common in traffic collisions as some kinetic energy is typically transferred into sound, heat or deformation.
  • An inelastic collision is more common in traffic collisions; momentum is conserved but kinetic energy is not.
  • Recognising whether a collision is elastic or inelastic can provide critical insight into the forces involved and aid in reconstructing the incident.

Impulse and Impact

  • Impulse is the product of force and time duration; in a collision context, it is the change in momentum of a vehicle.
  • Impact can be considered the collision of one object with another, critical for assessing areas such as the initial point of contact in a traffic collision.
  • Evaluating impulse and impact characteristics can help determine collision contributing factors such as speed and direction.

Role of Physics in Forensic Collision Investigation

  • Having a good grasp of motion and collision physics is essential for investigators as it enables them to unravel a collision’s sequence and contributing factors.
  • It helps in understanding aspects like force, speed, direction, and energy transfer during a collision.
  • Information deduced can assist in accident prevention and provide important evidence in legal proceedings.

Measures for Collision Prevention Based on Physics

  • Understanding the physics of movement and collision can help develop more effective safety measures.
  • This can guide the design of safer road layouts, improved vehicle safety features, and smarter traffic management systems.
  • More informed driver education on road safety principles can reduce the likelihood of collisions.