A crash is a rapid change in motion. The vehicle, its occupants and any other objects involved may experience different motions and forces over a short period. Understanding these changes helps explain why speed, restraint use and vehicle design matter.
Speed is only part of the story
The change in velocity during an impact is often described as delta-v (Δv). It is the difference between an object's velocity before and after the event, including direction. Two crashes at the same travel speed can produce different occupant loading because impact geometry, braking before impact, vehicle mass, structural response and contact conditions differ.
Energy and deformation
A moving vehicle has kinetic energy. During a collision, energy may be transformed into deformation of vehicle structures, motion of involved objects, sound, heat and other forms. Controlled structural deformation can help manage the crash event, but the outcome depends on the full crash configuration—not on one simple measure alone.
What is a crash pulse?
A crash pulse is commonly used to describe how vehicle acceleration changes over time during a crash. Its magnitude, duration and shape influence how the occupant restraint system loads and moves the occupant. Peak acceleration alone does not fully describe a crash pulse or establish injury outcome.
Why restraints matter
Seatbelts, pretensioners, load limiters and airbags are designed to manage occupant motion and distribute loads. They work with the vehicle structure as a system. Proper seatbelt use remains important even in vehicles equipped with airbags; an airbag is not a replacement for a seatbelt.
Key idea: Crash severity, vehicle damage and injury risk are related but not interchangeable. A technical reconstruction requires multiple sources of evidence and should not be inferred from a single photo or number.
Learn more
This is a simplified introduction, not a crash reconstruction, injury prediction or engineering analysis.
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