How do we explain when a person is involved in what appears to be a low speed impact but is suffering from a lot of neck pain. Does damage or no damage determine the extent of injuries that one can suffer? There is considerable misconception about the amount of vehicle crash damage is directly related to the degree of occupant injury. Today's post will show you how even minor car damage can major occupant injury and the injuries can be quite serious.
Plastic vs Elastic Deformation
Most people would expect that more injury will occur when the speed of the collision is greater. The truth is that this is the case sometimes especially when collisions occur at highway speeds. But in most cases even when the speed of a vehicle is very slow, with little or no damage, it can create a lot of pain. To understand this, we must understand the relationship between plastic and elastic deformity. When sufficient load is applied to a metal or other structural material like a car, it will cause the material to change shape. This change in shape is called deformation.
What happens when we hit something plastic vs something elastic? If you hit something plastic , most likely it will break or dent. In plastic deformity, there is more deformity to the car. With plastic deformity there is more metal crushing or more damage to the vehicle, the G Forces associated with the crash are absorbed by the crushing metal, which in turn exerts less g forces to the contents of the vehicle (you)- therefore less injury.
A temporary shape change that is self-reversing after the force is removed, so that the object returns to its original shape, is called elastic deformation. If you look at a vehicle that is stiffer, with less vehicle damage, the energy is not absorbed by crushing metal (elastic deformity), meaning that the occupants will be more jostled and thrown around to a greater amount. In this case more g-forces are exerted and there is a greater change of injury.vs elastic which will bounce back to its original shape. In elastic deformity there is less damage.
The Mathematics of Acceleration
Acceleration and Crush Distance can equal major injuries. In an automobile crash, acceleration is inversely related to how long the car moves before it comes to a stop (the crush distance).
where a=acceleration, V=velocity of impact, s=the Crush Distance.
Let’s look at 2 car collision scenarios:
- A car hits a brick wall at 10mph and crushes the front of the car 5 inches.
A=78.3 m/sec2, or 8 GS of Force
- A car hits a brick wall at 10mph. This car has a different car design and crushes the front of the car only 2 inches.
A=196m/sec2, or 30G’s of force.
As you can see, we have a collision with the same velocity, but with a different crush distance smaller by 2.5 times, will have a resulting G force 2.5 times larger!
Sometimes no serious visual deformation may occur on a vehicle even though it is subjected to relatively high speeds of impact. Often times motor vehicle bodies or bumper to bumper chassis give little or no crushing effect. Thus relatively high G forces can result in a whiplash injury. The use of stiff motor vehicle bodies and chassis will also produce a spiked G force loading to those in the car, even if little damage occurs to vehicle body or the frame of the car. So as you can see, even minor collisions can result in injury.
Injuries that can Result from car accidents
Injuries from a car accident can be be very serious. What may appear to be minor in the beginning- but can turn out to be quite major. Diagnoses related to auto accidents include: whiplash, herniated disc, Lower back pain or lumbago, stiff neck, carpal tunnel, nerve entrapment, TMJ disorder, and headaches. We'll save a detailed discussion for another blog post !
Source: Robbins, MC. Lack of relationship between vehicle damage and occupant injury.
Photo Courtesy of MikeWick on Flickr.com
Additional Resources:
Read more about Whiplash in our Special Whiplash series:
Part 1: Can whiplash cause shoulder pain?
Part 2: How does Whiplash Occur?
Part 3: What Symptoms are associated with a whiplash type injury
Part 4: Reducing Whiplash Injuries by 90% - just by changing One thing
Visit us on the web at Arc4life.com
Visit Arc4life.com for your online selection of the best products for neck pain relief including: Electrotherapy, Tens unit, cold pack, hot pack, neck stretches and support neck pillows.
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