View Full Version : how not to run a cat over?

05-12-2005, 08:19 AM
ok i was thinking that when an animal runs across the road it doesnt try to avoid a car.. i believe that when i see a animal run on the road i dont have time to think about what i should do so i try to devise a plan beforehand. i believe that i should swerve and that i should slow down.. if i hit the animal then i had done all that i could..

more so if it is a human then that human will try to avoid getting hit so i shouldnt guess which direction he/she will move instead slowing down *which gives the human more time to react* and not moving the position of the car from left to right is the correct action...

A. with a car or dog will slowing down decrease the odds of hitting the animal?

B. will slowing down decrease teh odds of hitting a human?

i dont need the math just the theory or idea

05-12-2005, 04:32 PM

05-12-2005, 04:41 PM

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If the magnitude of your velocity is that of light, you will hit cat or human with probability ~1. If your velocity is zero, the probability of carnage drops to ~0. So slow down.

*Going back to getting slapped around by life*

05-12-2005, 05:00 PM
If you turn left, the probability that you hit the cat/human drops to 0 as well. ALWAYS turn left.

05-12-2005, 05:34 PM
yah but i dont turn because then that adds another factor. say the human thinks about which direction i might turn in order to avoid it and the human runs left instead of right

05-12-2005, 09:45 PM
But if you turn directly left, your forward velocity is 0...making it impossible for you to hit him. We're not talking swerving here, we're talking TURNING!

05-14-2005, 02:25 AM

I am a cat. I usually like fish, but lately I have noticed a fish driving a car, and he is trying to run me over. He leaves a casino every night at 2AM, and he is always grumbling. Then he tries to run me over. Am I just having bad dreams, or could a fish really be trying to kill me.

PS. What are the odds of a fish being in a Casino?

05-14-2005, 02:04 PM
consider my attempt at an answer an extempore. Since you said the math is not important.

Lets make a few assumptions first. Dog is a point object. The width of your car is w.

Lets say you are moving at a speed of c and the dog is moving at a spped of d.

Also lets assume that when yo first notics the dog, it has started crossing the streeet ata random location. Its not a necessary assumption, but does not really alter our answer. So I make it for simplicity.

Finally you are at distance D from the dog when you notice him

This is by no means rigorous, but here is the general idea.

It takes you time T to iht the dog or miss him

T = D/c

In time T the dog can move a distance of D*d/c or Dd/c

Lets assume that the dog started at a location where if he stayed put, he would get hit the car a an offset x from the right corner of the car, and he is moving left.

Probability of hitting dog is 0 if Dd/c >=W -x
is 1 if Dd/c < W - x

Now maybe we can sum or inetgrate over all starting locations x and directions of movement to get a probability.

Looking at that bigger Dd/c lesser the chances of hitting

So slowing down is useful. However if the street is wider than one lane, we must include more parameters, and the results could be different. In fact I believe that we might get more than one minima, and in fact speeding up might be the better thing to do.

Neway the reaon I spent all this time typing this reply is to say,

If the car was travellin at the speeed of light, the probability of hitting the dog is _not_ 1. Just as you can move inside a room and not get to see the sunrise. That light is definitely travelling at the speed of light, and you are infinitesmally slower, but the distance between the sun and the earth allows you to avoid getting hit by that light, if you planned enough in advance /images/graemlins/cool.gif /images/graemlins/tongue.gif

05-14-2005, 03:31 PM
If you turn left, the probability that you hit the cat/human drops to 0 as well. ALWAYS turn left.

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but what if i'm not an ambi-turner?