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WoP #4: Car Crashes



A couple days ago, I was waiting to be picked up (since I'm a seventeen year old chicken who still doesn't have his license), and I unfortunately almost witnessed a car accident. A child, maybe four or five years old, went to chase after a ball which went across the street, and the driver couldn't see him because there was a parked car in the way. I tense up because I'm about ready to bolt over and help the kid, but luckily the driver stops about a yard away from hitting the kid. He's one lucky kid.

The weird thing about this, though, is that the force of friction acting on the car to move it forward before the brake is applied is the force of static friction, which is greater than the force of friction which acts to bring the car to a stop after the brake is applied, that of kinetic friction. This means that, in order for the car to come to a stop, the brake would need to be applied for a longer amount of time than the gas would to bring it up to speed, being kinetic friction has a lower acceleration than static friction.

In addition, the impulse the kid would've felt had he been hit would likely be enough to cause serious injury, considering the magnitude of the momentum of the car compared to the child's momentum in the direction of the car's motion (~0 kg m/s), and the fact that the car's velocity wouldn't change much due to the child's relatively small mass compared to the car. I truly am glad the car stopped in time, because human road kill isn't something I ever want to see.


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