Friction’s Forces

Dr. Edward P. Becker | TLT Automotive Tribology August 2018

The laws of our science update the old adage about steering into a skid.

Steering into the skid usually results in oversteering or understeering.
© Can Stock Photo / dbrus

The easiest (and safest) way to open a bottle of champagne is to use the laws of friction to your advantage. Here are the steps:

1. Remove the foil over the cork and cage.
2. Place a napkin or small towel over the cork and cage with your right hand (or left, if you are left-handed). From now until the bottle is open, your hand does not leave the cork! If the pressure in the bottle is sufficient to force the cork out on its own, your hand will catch the cork and prevent damage or injury.
3. Loosen (but do not remove) the cage.
4. Holding the cork and cage stationary, grasp the bottle near the base and twist the cork with your other hand. Do not pull on the cork! As you twist, the cork will move out of the bottle and release with a festive pop.

Before you start twisting, the friction between the cork and bottle is sufficient (usually) to keep the cork from moving. Once you start twisting, however, the cork will move in the direction that is normal to the resultant force of your twisting plus the internal pressure. If you find you need to pull on the cork, the champagne has gone flat.

The same principles apply, in reverse, when a vehicle begins to skid. Whether due to ice, rain or just driving too fast, we can define a skid as beginning when the bottom surfaces of the tires are moving relative to the pavement, i.e., sliding. As with the champagne cork, the vehicle now moves in the direction of any resultant force and does not respond to steering. To restore control, the contact between the front tires and pavement must be brought to rest.

The old advice of steering into a skid has been a source of confusion, as this has been interpreted in various ways and usually results in turning the steering wheel too far in one direction or the other (oversteering or understeering, as the case may be). Likewise, there is conflicting information on whether or not to apply the brakes, or even the accelerator, during a skid. However, modern anti-lock brakes and traction control can compensate for these inputs.

The second best generic advice, therefore, is to steer in the direction you want the vehicle to go, neither over- or understeering. Once the relative motion between the tire and pavement stops, force can be transmitted to the vehicle in any horizontal direction, allowing the driver to return to a safe path.

The best advice, of course, is not to drive too fast for conditions and avoid going into a skid in the first place!
Ed Becker is an STLE Fellow and past president. He is president of Friction & Wear Solutions, LLC, in Brighton, Mich., and can be reached through his website at