Einstein’s concept of relative motion can help everyone understand the dangers of car collisions. You may ask yourself, What does the theory of relativity have to do with car collisions? In fact, there is a real-life connection and it helps us understand how safe we are from injury when traveling in a vehicle at different speeds.
According to Einstein, if two different objects have the same velocity, it does not really matter if one is not moving or both are moving. Any interaction between both of those objects would be identical, even if one was not moving or they were both moving.
Energy Problems
Some experts believe that the energy generated in a car crash that involves two vehicles is different depending on the situation, even if the velocity between both vehicles are the same. Their argument is that a vehicle traveling twice as fast as the other vehicle involved in the collision would have four times the amount of energy (kinetic energy), because of the formula used for kinetic energy (K = ½ mv²).
Because of this formula, many of these experts say that a vehicle colliding with a stationary vehicle will have twice the energy of both vehicles compared to both cars traveling at half the speed and colliding head-on with each other. This means that the first collision would cause more damage than the second, even though both collisions have the same relative velocity. Who is correct? Even Einstein was concerned about this difference.
Two Collision Scenarios
By reviewing two collision scenarios, we can understand these different beliefs more clearly. The two collision scenarios will be inelastic and elastic. The inelastic collision occurs when both vehicles stay in contact with each other throughout the collision. The elastic collision occurs when both vehicles bounce, or deflect, off each other with the same relative velocity they had when first colliding, but go move in different directions.
Let us take the inelastic collision. Two vehicles are moving toward each other at the same rate of speed. According to the laws of physics, conservation of momentum, mass times velocity is the same for both vehicles preceding the collision and after the collision. If there is a head-on collision, then both vehicles will come to a complete stop and the damage would be the same.
However, if one car is stationary and the other car is moving, once the collision occurs, both cars would be moving at half the speed, but damage would still be the same.
In an elastic collision, these two scenarios, the energy is not lost, but transferred. Imagine two ball bearings hitting each other. The bearings would bounce off of each other at the same rate of speed. So here the velocity is not the problem, the forces imposed on the passengers would cause the problem. This means that all that energy created by the relative energy of the collision would be transferred to the passengers.
Final Results
Now that we have looked at both collision scenarios, we have learned that a vehicle in motion or stationary. What really matters is whether the vehicles remain in contact with each other after the collision or whether they bounce off of each other. When the cars are involved in an elastic collision, the passengers have more of a chance of being injured than they would in an inelastic collision.
Another concern that has been studied when it pertains to automobile accidents is the rate of speed the collision occurs. According to a study conducted by the University of Adelaide, casualty accidents greatly increase as the speed of the collision increases, but the most dramatic increase in casualty accidents occur 64 percent more when the collision occurs when a car or cars are traveling over 60 mile-per-hour (mph).
While all of this seems confusing, vehicle collisions are a major cause of death to people of all ages. Even though most of the car accident deaths occur at higher rates of speeds or when cars bounce off of each other, Einstein’s concept of relative motion will always come into play. Hitting something stationary, hitting another car head-on or whether both cars are moving makes no difference. Both vehicles and passengers can be damaged just as much.
