Fun with Physics question

[Tele 'til You're Smelly]

If you are stopped in your car (but not parked) and see in your rear view that you about to get hit from behind, are you better off in terms of injury braking or not? Assume for the moment no one is in front of you. And then what if there is someone in front of you?

Click & Clack address it somewhat here http://www.cartalk.com/content/braci...t-better-brake but they are talking more about vehicle damage. Let's say someone is really screaming in behind you and injury is really all you are worried about.

No reason for asking this today, just one of those random thoughts I have sometimes.

[aqua toque]

Are you on a treadmill?

[riser3]

Hold my beer while I jam it in reverse and floor it!!!

[BillyFromTheHills]

My guess would be to stomp the accelarator, or at least not brake, to reduce the power of the impact....but you'll go right into the intersection

[cesare]

I got rear ended twenty years ago by a truck that I never saw while rolling and waiting to merge to a single lane. I don't recommend it unless a life of amnesia, tinnitus, trigeminal neuralgia, insomnia, and associated cognitive deficit is your goal. I have always thought if I had braked and braced, my body wouldn't have accelerated so far in front of my head. Who knows?

I want my month of zero memories back.

[bobs]

I'm guessing it doesn't make much difference; either way your vehicle is going to be displaced a fair amount (happened to me a couple of years ago, rear-ended by a small pickup, and I was sent forward with enough force to partly crumple the front of my car when it hit the minivan in front of me; I'm pretty sure I had my foot on the brakes, as I had just come to a full stop before getting hit).

[cesare]

Well, there's that. Like I said, who knows?

[Charley White]

Hey, I'll play. Slightly better than the jump before hitting in falling elevator. Not much, as Cesare and Bobs said. But if you were measuring micro-newtons, I'll vote brake. Every action; equal & opposite. Whatever the force of hitter, you and car receive. With no resistance=>full rapid acceleration and all organs & brain squashed against ribs & skull. With more friction resistance, more car crumpling before organs and brains squash against ribs & back.

[BillyFromTheHills]

But wouldn't the force be less if the two vehicles were travelling at similar speeds at impact? I'm talking about accelarating vs. brake/no brake... If brake/no brake are the choices, then I vote no brake.

[James]

This one is easy. Do you want your car to take the impact or you. If the former hit the brakes as hard as you can.

[bobs]

Yes, traveling at similar speeds it would better not to brake since braking would increase the relative speed at impact. But in nearly all cases, a rear-ender occurs while the front car is decelerating (or stopped), and doing so because they have no choice but to decelerate. The original question almost only makes practical sense if the car whose driver is contemplating this corundum is fully stopped.

[aqua toque]

.... if the car whose driver is contemplating this corundum is fully stopped.

Corundum? Damn near killed 'im!

[tele.skier]

the space shuttle docks with the space station at over 17,000 MPH.... Do ya think the rate of speed matters more than the difference in speed?...



Looks good to me...

[James]

and it does not matter what that difference in speed is so long one car hits the other then the occupant is always better off hitting the brakes. Now if you are more worried about the car then yourself then by all means hit the gas.

By the way this is pretty common question/ answer in drivers edd and safety courses.

[Grant]

Assuming the impact is inevitable, you need to consider Delta V (change in velocity) to determine how the seat back and headrest move forward in relation to the momentarily stationary driver or passenger. If the struck vehicle moves more slowly (due to braking) there is a lower likelihood of injury.