The Traffic Accident Reconstruction Origin -ARnews-

Re: Is Drag Factor Velocity-Dependent or Not?

Bruno Schmidt (SchmidtBF@aol.com)
Tue, 17 Jun 1997 07:39:25 -0400 (EDT)

Laws of friction should be put in quotation marks (along with many other so-called laws) because they are not true physical laws but usually rather good approximations to the way nature behaves. As such, the "law of friction" should say that the friction force is approximately independent of surface area, is approximately proportional to the normal force, is approximately velocity independent. To state the actual behavior more precisely requires careful experimentation and testing. Therefore, we cannot invoke such a law as having universal validity.

As a side note, even Newton's laws of motion, which can be applied with complete confidence to moving vehicles, are only approximations. As the velocity of an object approaches the speed of light (not something we see in collisions), trying to use F = ma will not lead to the correct relationship between the acceleration of an object and the force acting on it. The acceleration will actually be less than what the formula suggests. Therefore Newton's second law of motion is only an approximation--albeit a very, very good one at ordinary speeds.

NOTE: You are reading in an archived session of ARnews. It is possible that this topic is still being discussed. To see if this topic is still active, or of there were any more recent posts on this topic, check later archives of ARnews.

If there is no current post, and you would like to add to this topic, link to the Current ARnews Discussion and begin a new thread. Be sure that if you are starting a new post that the thread title does not contain the abbreviation RE: Placing RE: at the beginning of a new post will confuse Hypermail and prevent others from answering your post in the future.

For example, to continue this discussion look for a thread titled

Is Drag Factor Velocity-Dependent or Not?

If this thread does not exist in the current archive, you can begin another one by using that title.