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F = MA and the human element

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Jim Thompson

By Jim Thompson
HCP columnist

F = MA is an equation from physics. It means Force equals Mass times Acceleration. You use it every day, even if you never took physics.  

It is represented by two pedals in your car: the accelerator and the brake. The car provides the mass (just call it "weight," for the moment) and the equation solves itself from there.  

Deceleration (the application of the brake pedal) is just the opposite version of acceleration, same equation applies. Force is the result.

In the 1960s, I and many other young boys, read a magazine called Mechanix Illustrated. We read it for the prose written by one Tom McCaHill (pronounced Maw-Kay-Hill – Jay Leno, in his car videos, always messes up the pronunciation).  

Uncle Tom, as he liked to be called, tested cars and wrote some of the most memorable and hilarious car test reports produced to this day. In his serious moments, he said he would stop testing cars when his reflexes – his reaction time – exceeded 0.10 seconds. How did he test this? By jabbing a stop watch twice, as fast as he could. 

I just did it with my phone stopwatch, and the fastest I could do it was 0.20 seconds. I am slow.

So what? If you are traveling at 60 miles per hour, that means you are moving at 88 feet per second (an aside, that is where name for the Oldsmobile 88 came from). In a tenth of a second, you travel 8.8 feet; in two tenths of a second, like me, you travel just over 17.5 feet. This means, in a sudden automobile accident, I would drive about one car length through the site of the accident. Except F = MA stops me before this – if the pavement is dry, and there is decent tread on my tires.

If we are in a modern automobile, seat belts and air bags take over and keep our bodies from trying to prove F = MA. If we are on a motorcycle (or in a Mennonite buggy), well, nothing much has changed in the last 100 years. F = MA appears with a vengeance.

On Friday night, June 30, I lost my second friend in the past two-and-a-half years on southern Ohio highways due to the combination of F = MA and human reaction time.  

This latest accident was on U.S. 50 at Rapid Forge Road. This time my friend was on his motorcycle. The earlier incident involved a Mennonite buggy on U.S. 62 on Feb. 2, 2021. No seat belts or air bags were available in either case.

In 2018, I gave away my motorcycle. Despite having changed its equipment to an “always on” flashing headlight (legal in most states), flashing brake lights upon application of the brakes, and an extra loud horn, I knew these appurtenances would not compensate for that nasty 0.20 second reaction time. It was time to hang it up. I was 68 years old.

Princess Di died by the application of F = MA. In her case, the blood inside her aorta supplied the mass, and the stop was so sudden, the wall of the aorta could not contain the mass. Tiny Mass, but monstrous deceleration. This is often what has happened when you read someone died of “internal injuries.”  

One more example of F = MA. On YouTube, there is a channel called “Virtual Rail Fan.” There, I watched a train hit a car at a crossing. It took the train one minute and 15 seconds to come to a stop. The car was obliterated. Big “Mass” in this case, not so big “Acceleration,” but F = MA demanded its due.

I am not here to tell you what to do. But I am here to tell you that F = MA is inviolable, and your reflexes are reality, no matter how young you feel.  

Be safe.

Jim Thompson, formerly of Marshall, is a graduate of Hillsboro High School and the University of Cincinnati. He resides in Duluth, Ga. and is a columnist for The Highland County Press. He may be reached at


Matthew (not verified)

3 July 2023

Automobile accidents scare me the most. For me and everyone else who travel on public roads. A cautious driver can do everything right, but that other driver has to do the same. Then there's passengers involved too... I recently drove 38,000 miles a year. Now it's about 28,000 miles annually. Besides the State of Ohio's multiple deer, I've had only one motor vehicle crash. Luckily, both single occupants walked away. The Dodge and the Chevy rolled no more. It has been my only ticket in 30 years. As a side note, the head and neck injuries of a sudden impact (think Dale Earnhart) are probably more common than the Princess Di situation. Automobiles hitting head on or a single vehicle into a tree (or retaining wall) is not good.

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