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## Main Question or Discussion Point

*I am writing an essay in which I try to describe Centripetal Force to a layperson. Since I am a layperson myself, I wanted to make sure that there were no glaring errors before I submitted it. If someone could review this, and let me know if it passes scientific muster, I would appreciate it. Thanks.*

That seer of seers Sir Isaac Newton observed that any motion in a curved path represented

*accelerated*motion---and thus required a force directed towards the center of the path, otherwise known as

*Centripetal*

*Force*(not to be confused with its popular cousin

*Centrifugal*

*Force*, which means something else entirely and shall not be mentioned again).

Centripetal Force is a term that suffers from the confusion between Speed and Velocity. So here now is the official difference between Speed and Velocity:

If you’re in a car going 30 miles per hour in a straight line, then 30 mph is both your Speed and your Velocity.

If, however, you’re in a car going 30 mph in a straight line, then make a 30 mph left turn, your Speed is still 30 mph, but your Velocity has

*increased*, because Velocity measures your rate of motion

*plus*the change in your direction of motion.

So a race car driver might be driving in circles at a constant speed of 200 mph, but by definition he is actually accelerating (i.e., increasing his velocity) the whole time. Basically, if you’re covering more area at the same speed, a

**C**instead of an

**I**, some component of the equation must also be increasing. This component is called Velocity. It’s like Speed in three-dimensions. The greater the curve, the more you have to accelerate to cover the same amount of distance in the same amount of time. The moral of the story is,

*When turning, you’ve got to accelerate just to keep up.*

So for an object to orbit at a constant speed around another object---the Earth turning around the Sun, the Moon turning around the Earth, an electron turning around a nucleus---it must be accelerating. An orbiting object, moving in a circle---turning around a central point---can be said to be accelerating inwards towards that point.

According to Newton’s Second Law of Motion (the No Freebies clause), an object that accelerates must therefore be getting some kind of push in the direction of the acceleration. And if this object is accelerating inwards, ergo, there must be an inwardly-directed force acting upon it. This push towards the center is called “Centripetal Force”. The word

*centripetal*literally means

*center-seeking*.