Acceleration can be a drag. It is the first topic in many physics courses which is confusing to some students. Both speed and acceleration describe motion, and it is easy to not clearly distinguish between them. After all, one presses on the accelerator to speed down the highway. But having this problem does not mean someone is stupid--there have been some really smart people who have done that, too. One of the most notable is the author of the defining text Physics.
The first physics text was written over two thousand years ago by a Greek philosopher named Aristotle, who engaged in a life long effort to systematically analyze all areas of knowledge, including how the physical world works. Like modern physics texts, it discussed motions and forces. Unlike them, it never introduces the idea of acceleration. The only kinds of motion it discussed were constant speed, stating that things would go twice as far in twice the time. That didn't stop Aristotle's work from serving as a definitive text for nearly two thousand years. The concept really wasn't needed.
Acceleration is not an intuitive concept. Even a five-year-old can tell the difference between things in different positions or moving at different speeds. Acceleration, however, is about the rate at which the speed is changing, which is not something most kids pay attention to. When running hard is high speed and time is told by the part of the day, not a stop watch, acceleration is not really an important concept.
That, of course, was the situation for Aristotle. He just kind of assumed that constant speed motion was all that really mattered, and most certainly did not distinguish between acceleration and velocity. There is a certain similarity between Aristotle's work and the novice physics student that does not clearly distinguish them. But at least in Aristotle's case, it was not due to sloppy thinking. First, his analysis of the world was conceptual, not numerical. He wasn't trying to calculate anything. Second, when the primary time keeping method is the passage of the sun across the sky and a galloping horse was high speed, periods of acceleration were not something that could really be measured. Third, the mathematics of his day did not facilitate developing the concept of acceleration. But then things changed, and people like Galileo and Newton came along.
Galileo and Newton were both mathematicians, not general philosophers, who brought a quantitative approach to studying the world. Time keeping advanced greatly with Galileo's invention of the pendulum clock. Algebra was introduced to Europeans during this time from Arab scholars, and Newton invented calculus. Physics became mathematically rigorous, with a different outlook, improved experimental equipment and calculational tools. This resulted in a need to be able to describe motion more precisely; an undistinguished quality of motion was no longer sufficient to describe the world around us.
Aristotle's description of motion was intuitive; modern descriptions less so. That is the problem for beginning physics students. Intuitive thinking is what we tend to default to, and until it has been well trained, it tends not to be very precise. There is a place for that level of thinking, but it won't enable us to produce precise descriptions of motion, especially things like drag racers.
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