i94It was early Saturday morning when I headed home from giving a long evening lecture at a city 3-hour drive away. I was "leisurely" cruising at 85 mph on I-94 freeway along with other fellow motorists (I know, I know, the posted speed limit is 65, but sometimes you just have "to go with the flow" 🙂I was in the front position, until we were closing-in to a car with a low trailer on the leftmost lane. I decided to pass from the right lane, but just before changing the lane I saw a big refrigerator (family-size frig) suddenly "jumped out" of the trailer. The frig was probably not fastened properly, so it snapped — and the trailer siding is only a few inches high. Something unusual happened in my head … I was not panic at all. All that came to my mind was the Newton's First Law of Motion — if you still remember your highschool physics: "An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force."

 

In laymen's terms it says that the refrigerator pops out with the speed of 85 mph, and will slow down only because of forces acting upon it, namely kinetic friction (friction to the pavement) and drag (wind resistance). So forget about what you see in the movies — that objects from the car in front of you come smashing at your windsheld — that's not a very realistic physics model. I still have the full control of the car. Of course, I can't just turn off the engine or make a sudden stop — lest the cars behind me may not have enough time to react and setting up a multiple crash, a fenomenon known as "piling up" [like the accident caused by the SBY convoy's disruption at the freeway.] I can't make a sudden sharp turn either, because of the risk of rolling over … mind you, the car was at 85 mph!  In those fractions of a second my mind does a quick calculation on the classical mechanic modelling and immediately implementing a course of action … I started braking but kept staying in the same lane, literally "following" the refrigerator. My model dictates that I have an advantage of having rubber tires which have larger friction-coeficient of rubber-to-pavement than that of the smooth-metal refrigerator body. Another factor to my advantage is the ABS (anti-locked brake system) installed on most modern car today, making my friction-coefficient even larger because of the "static" instead of "kinetic" friction experienced by the refrigerator. [Okay guys, this is your homework, try to figure out the physics model: why is it static that happens in ABS, and not kinetic friction?(**)].

 

After what seemed to be the longest seconds in my life — that translate to an estimate of a couple hundred feets — both objects, the car and the refrigerator, came to a full stop. The distance between us, bumper-to-bumper (or the back of the frig in this case) is less that 3 feet. Not bad for a first-timer, huh?

Note:

(*) When a colleague asked my permission to share this article with her class I immediately agreed, but I added a subtitle to it: "Oh, how I was almost killed by a refrigerator … and how science has saved my ass"

(**) I owe this ABS-thingee to professor Richard Wolfson, a professor of physics at Middlebury College where he has taught for over 25 years. I watched his lecture series "Physics in Your Life" in the previous weekend.

Salute,

KM/