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Re: [Phys-l] car skidding and spinning



I always thought that the advice to "steer in the direction of the skid" was some of the most useless advice ever given.

What exactly is the direction of the skid? There's a linear direction, and a rotational direction. If you steer towards the direction of the linear displacement, you can arrest the skid. If you steer further into the rotational direction, you won't stop the skid, and you may even increase the rate of rotation.

The advice should be to turn in the opposite direction of whichever way you turned to cause the skid. If the skid was caused by braking, where the back end of the car is coming around, you've got to steer opposite the direction of rotation.

If you over correct, you'll start an oscillation that will quickly send you out of control.

Your strategy may also depend on what is in your path. If you can avoid a tree by skidding even further, then it helps you to do that. If you can collide with a barrier while going backwards, you may be less injured that if you hit it head on. If the strategy would send you into oncoming traffic, it's a bad one.

At high speeds, it all happens too fast to do much about it anyway unless you've practiced it.

Scott


On 12/5/2011 11:04 AM, phys-l-request@carnot.physics.buffalo.edu wrote:
Message: 2
Date: Mon, 5 Dec 2011 04:15:00 +0000
From: "LaMontagne, Bob"<RLAMONT@providence.edu>
Subject: Re: [Phys-l] car skidding and spinning
To: Forum for Physics Educators<phys-l@carnot.physics.buffalo.edu>
Message-ID:
<9DD8E6B7DA56BD4CA13E0C068DA57218432CC965@DAG01.providence.col>
Content-Type: text/plain; charset="us-ascii"

If you turn into the skid you decrease the friction on the front end of the car because the wheel can roll instead of skid. This decreases the torque from the front and the car tends to straighten out. This is an old "dirt track" trick. It also works great on snow covered roads.

Bob at PC

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