physics of car accidents

Have you ever wondered how police officers and car accident lawyers in Denver determine who’s at fault in collisions? Although many might not know it, their presentation of collisions in court has much to do with physics. 

In this article, we’re looking at what determines the physics of car accidents. Continue reading to learn more about how Newton, force, and energy, might save your life if you find yourself face-to-face with a car wreck. 

Force: Wall Collisions

To understand the physics of car accidents, we first have to look at Newton’s Laws of Motion. Newton’s first law is the law of inertia and it asserts that objects in motion will stay in motion until acted upon by an external force. If the object is at rest, it will remain at rest until unbalanced forces act upon it. 

Car A collides with a static wall. It begins with car A traveling at a specific velocity (v) and after colliding with the wall, it ends with a velocity of 0. Newton’s second law of motion equates that force equals mass times acceleration. Taking this into account, we see acceleration is (v-0)/t. T represents the time it takes the car to stop. 

While the car exerts a force in the direction of the wall the wall exerts an equal force on the car. This is according to Newton’s third law of motion: for every reaction, there is an equal and opposite reaction.

If the car slams into the wall and the wall is strong enough to withstand that force, the force still has to go somewhere. Instead of exerting the force onto the wall, the wall deflects the force of the car backward, creating that accordion you’re used to seeing in the crash dummy sequences. 

Force: Colliding with a Car

In this situation, one car collides with another. This example assumes the cars are replicas of each other and travel the same speed but in opposite directions. Using the law of conservation of momentum, we understand they must come to rest. The mass is the same and the force experienced by cars B and C would be identical. This explains force, but we need to understand energy to fully understand the collision. 


Each car has kinetic energy before the collision. After the collision, the kinetic energy of the system is 0. When the cars collide, the kinetic energy converts to some other form of energy, be it heat, sound, etc. In the example of the car colliding with the wall you only have one object with kinetic energy. With two cars colliding, both objects have kinetic energy, which creates a more energetic collision. 

Considering Cars and Particles

At the quantum level of particles, energy swaps between states. When applying this understanding to our two above examples, one can see why the two cars colliding with each other will often produce more detrimental effects than the single car collision with the wall; there is twice as much energy involved. Some of the reason for this is when the cars collide, they effectively fuse, as pieces of each fly in opposing directions. 

Looking at the way these particles behave is the reason why physicists accelerate particles in colliders. It gives them the ability to study high-energy physics. Colliding two beams of particles in a particle collision reveals the energy of the particles, 

Minimizing Impact

Taking these elements into account, you can always do something to minimize the force of impact if a collision is inevitable. You might only have a few seconds to assess the situation, but if you engrain these tips, it might save your life. 

Reduce Speed 

Part of how much energy gets produced by collision is the speed at which you travel. Any speed reduction will automatically decrease the severity of your accident. Use controlled braking to avoid skidding and steer in a way that gives you time to reduce speed. 

Hit Something Softer

If you can’t slow down or avoid the collision, try to steer to something softer. Bushes, guard rails, and crash barrels are better than trees, concrete walls, and other vehicles. 

Side Impact Is Better than a Head-On Collision

If you are on track to hit another vehicle, you should consider lessening the severity of the incident by hitting a different vehicle on the side. 

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