[Physics] Is a collision with an immovable object equal to a head-on collision?


Scenario 1

Two identical and bilaterally symmetrical cars, driven by identical drivers in the exact center of the car and in the same body position, each traveling the same speed, collide exactly head on. (Essentially, eliminate all variables that would cause rotation or interpenetration during the collision).

Scenario 2

One of the above cars hits an immovable wall instead of an oncoming car.


Will each car in these scenarios experience the same forces? For clarity, the cars in scenario 1 have twice the closing speed of the car and wall in scenario 2.

Best Answer

Basically the answer is that yes, the two cars colliding at a closing speed of $2v$ is the same as a single car hitting an immovable wall at a speed of $v$. The argument is that the cars involved lose the same amount of kinetic energy, $\frac{1}{2}mv^2$, during both crashes, and this energy can go into bending the cars by the same amount.

In detail the forces experienced are likely to be different in the two collisions. Unless you can make both cars identical, and have them crash precisely lined up, during the crash the cars will deform each other asymmetrically and the force:time curve will be different from a crash into an unyielding wall. However the end results will be broadly similar.