
Understanding Speed & Velocity
Posted on August 17th, 2010 No commentsUnderstanding mechanics is nothing to do with mathematics, it is the reality of what is actually happening and why it is happening.
Speed and velocity
In practice speed and velocity have exactly the same meaning. Speed comes from the AngloSaxon/Dutch/German, and Velocity comes from Latin. Both derivations mean speed in the sense that the public understand it. However the physics establishment has decreed that velocity now means speed in a particular direction. Unfortunately, having confused the public with the change in meaning, they now appear to just as confused themselves, because they are constantly referring to cases that are clearly ‘speed’ and calling it velocity.
A typical situation is where they refer to the ‘velocity’ of a wheel. No point on a rotating wheel has velocity. All points on a rotating wheel have speed.
Obviously the above statements only apply in a situation where the centre of rotation is fixed. If we consider the wheel of a car travelling at 50 feet/sec along a perfectly flat road then the velocity of the wheel is 50 feet/sec. This refers to velocity of the centre of the wheel. Ignoring the resilience of the tyre, the speed of the wheel’s outer edge is 50 feet per second. ( Due to the resilience of the tyre the speed must be greater than this). The outer edge of the wheel does not have any velocity because it is never travels in a straight line.
Note: Newton was aware of this problem when he created his calculus but the physicists ignored it, and used Leibniz’s version of the calculus instead, in fact Newton’s calculus is almost never used and the modern calculus is the simpler Leibniz version.
Although this may seem a minor point it does present major logic problems in understanding the mechanics of rotary motion. The mathematics of rotary motion work but are completely illogical regarding the reality of rotary motion. This was evident even in school when much protestation was made about the lack of logic in the maths. Eventually the teachers agreed with us but argued that as it worked we should ignore the logic.
Note the following statement attributed to Einstein
“As far as the laws of mathematics refer to reality, they are not certain: and as far as they are certain, they do not refer to reality.”Brian Williams
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2 responses to “Understanding Speed & Velocity”

Nice share, good article, very usefull for me…thank you

But When we talk about instantaneous speed or velocity , the time interval is really short.At that short an interval, the distance and displacement has got to be the same? i really don’t understand why everyone is saying speed is equal to the magnitude of velocity vector.
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