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Difference Between Speed and Velocity ?

by Xidike
Tags: difference, speed, velocity
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Nov9-12, 04:58 AM
P: 3,916
Quote Quote by Xidike View Post
then why car has speed instead of velocity
The car has both. The speedometer shows just speed.
Nov9-12, 09:31 AM
jtbell's Avatar
P: 11,625
If you mount a compass next to your speedometer, you now have a device that tells you the car's speed and direction... voilà, a velocityometer!
Nov9-12, 11:36 PM
P: 125
Try " Wolfowitz, velociraptor" for a linguistic clue.
Nov10-12, 05:58 AM
P: 141
One way to think about it:

Distance is how far you've moved, ignoring direction. So if you go 5 km north, then 5 km east, then 5 km south, then 5 km east, you've traveled 20 km.

Displacement is the distance of the shortest path from start to finish, or as the crow flies) including the direction. So in my example above, you'd have a displacement of 10 km east (5 km east + 5 km east, the north and south cancel out)

Average Speed is distance/time
Average velocity is displacement/time
Nov12-12, 10:59 AM
P: 72
what is initial velocity and final velocity ??
Nov12-12, 11:07 AM
P: 141
Quote Quote by Xidike View Post
what is initial velocity and final velocity ??
Initial means starting. If you start from rest, your initial velocity is 0.

Final velocity is whatever your velocity is at the end of the time interval.

For example, if I am going 10 km per hour east and I speed up to 50 km per hour east, my initial velocity is 10 km per hour east, my final velocity is 50 km per hour east. If it took me 10 seconds to speed up, then my acceleration is 40 km/h/10 s or 4 km/h/s east.
Nov18-12, 08:58 AM
P: 19
Quote Quote by Hetware View Post
When did Gibbs's vector concept really take hold?
Gibbs, the father of vector analysis in physics, seems to have established this tradition of using the words speed and velocity for the scalar and the vector, respectively.

Gibbs's lecture notes on vector analysis and its use in physics circulated in a small circle since 1881. The publication of "Vector Analysis", the textbook based on his assembled notes (1901), had a huge influence. In the book, Gibbs recommended using the words speed and velocity as follows: Velocity is a vector quantity. Its direction is the direction of the tangent of the curve described by the particle. The term speed is used frequently to denote merely the scalar value of the velocity. This convention will be followed here.

That recommendation was repeated by a popular physics textbook that was published a few years later: "A Textbook on Physics" by Duff (1909): For clearness such a phrase as 'twenty miles an hour' may be called the statement of a speed, which means the mere magnitude of a velocity without reference to the direction.

Before Gibbs the distinction between the words speed and velocity was less clear. For example, Maxwell discussed speed, velocity, vectors and scalars in his book "Matter and Motion" (1877). He said: The rate or speed of the motion is called the velocity of the particle, and its magnitude is expressed by saying that it is such a distance in such a time, as, for instance, ten miles an hour, or one metre per second.

* Vector analysis: a text-book for the use of students of mathematics and physics, founded upon the lectures of J. Willard Gibbs, by Edwin Bidwell Wilson, 1901.
* Gibbs 1901 Duff 1909 Maxwell 1877

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