Crash Dynamics: Speed on Force of Impact

Understanding Crash Dynamics: Speed on Force of Impact

Speeding is a critical factor in accidents. Since 2003, speeding has been a factor of nearly one-third of crash deaths! This sounds like a lot of accidents attributed to a single factor, but this information is supported by physics. When something has a greater mass (weight) or speed (velocity), it has more kinetic energy. Kinetic energy is motion related energy, and it is very important to understand when considering the dynamics of a crash.

Kinetic Energy Equation

KE= ½ m(v^2)

This equation is fundamental when looking at the relationship between speed and the force of a vehicle impact. It means: the kinetic energy is equal to half of the mass times the squared velocity. To put this into perspective, consider the example below.


If you have a 2,000 kg car (which is about 4400 lbs) that is driving at 10 m/s (or about 22 mph), you would have a kinetic energy of 100,000 Joules. If you doubled your speed to 20 m/s (which is about 45 mph), your kinetic energy would be 400,000 J. In this example, it is clearly apparent that higher speeds will result in higher energy crashes. By doubling your speed, you increase the energy in a collision by FOUR TIMES, which makes it significantly more dangerous.


semi truck crash into small car


Why This Matters

Since increasing speed can result in extremely dangerous and forceful car crashes, it makes sense that slowing down can increase your chances of survival. In fact, the key difference between a crash where you can walk away compared to one where you are carried away has to do with the length of time during a crash. If your car is moving at a high velocity, there won’t be any time for the energy to be absorbed by the various safety devices. A few examples of a vehicle safety device are crumple zones and air bags. Crumple zones are sections of your car that are designed to crumple up and absorb energy from collision impacts over time. Air bags, too, extend the time of impact and give passengers their best chance for survival.


The MORE energy that a car absorbs during a collision, the better chance you have for survival. If you have ever seen a car get hit and the car still moves after the initial impact, it is probably because there was too much kinetic energy that wasn’t absorbed by the car. If more energy had been absorbed by the car, then less will be spent moving the vehicle in an unpredictable direction.


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