16 Aralık 2013 Pazartesi

The Vectors

THE VECTORS

This is a vector:
A vector has magnitude (how long it is) and direction:
The length of the line shows its magnitude and the arrowhead points in the direction.
You can add two vectors by simply joining them head-to-tail:
And it doesn't matter which order you add them, you get the same result:

Subtracting

You can also subtract one vector from another:
  • first you reverse the direction of the vector you want to subtract,
  • then add them as usual:

Other Notation

A vector can also be written as the letters
of its head and tail with an arrow above, like this:

Calculations

Now, how do we do the calculations?
The most common way is to break up a vector into x and y pieces, like this:
The vector a is broken up into
the two vectors ax and ay

Adding Vectors

And here is how to add two vectors after breaking them into x and y parts:
The vector (8,13) and the vector (26,7) add up to the vector (34,20)
Example: add the vectors a = (8,13) and b = (26,7)
c = a + b
c = (8,13) + (26,7) = (8+26,13+7) = (34,20)

Subtracting Vectors

Remember: to subtract, first reverse the vector you want to subtract, then add.
Example: subtract k = (4,5) from v = (12,2)
a = v + -k
a = (12,2) + -(4,5) = (12,2) + (-4,-5) = (12-4,2-5) = (8,-3)

Magnitude of a Vector

The magnitude of a vector is shown by two vertical bars on either side of the vector:
|a|
OR it can be written with double vertical bars (so as not to confuse it with absolute value):
||a||
You can use Pythagoras' theorem to calculate it:
|a| = √( x2 + y2 )
A vector with magnitude 1 is called a Unit Vector.

Vector vs Scalar

When using vectors we call an ordinary number a "scalar".
Scalar: just a number (like 7 or -0.32)  definitely not a vector.
A vector is often written in bold,
so c is a vector, and it has magnitude and direction
but c is just a value, like 3 or 12.4
Example: kb is actually the scalar k times the vector b.

Multiplying a Vector by a Scalar

When you multiply a vector by a scalar it is called "scaling" a vector, because you change how big or small the vector is.
Example: multiply the vector m = (7,3) by the scalar 3
a = 3m = (3×7,3×3) = (21,9)
It still points in the same direction, but is 3 times longer
(And now you know why numbers are called "scalars", because they "scale" the vector up or down.)

 Multiplying a Vector by a Vector (Dot Product and Cross Product)

How do you multiply two vectors together? There is more than one way!
  • The scalar or Dot Product  (the result is a scalar).
  • The vector or Cross Product (the result is a vector).(Read those pages for more details.)

More Than 2 Dimensions
The vectors we have been looking at have been 2 dimensional, but vectors work perfectly well in 3 or more dimensions:

                                   

Example: add the vectors a = (3,7,4) and b = (2,9,11)
c = a + b
c = (3,7,4) + (2,9,11) = (3+2,7+9,4+11) = (5,16,15)

Example: subtract (1,2,3,4) from (3,3,3,3)
(3,3,3,3) + -(1,2,3,4) = (3,3,3,3) + (-1,-2,-3,-4) = (3-1,3-2,3-3,3-4) = (2,1,0,-1)

Example: what is the magnitude of the vector w = (1,-2,3) ?
|w| = √( 12 + (-2)+ 3) = √( 1+4+9 ) = √14

Magnitude and Direction

You may know a vector's magnitude and direction, but want its x and y lengths (or vice versa):
<=> Polar and Cartesian Coordinates
Vector a in Polar
Coordinates
Vector a in Cartesian
Coordinates

You can read how to convert them at Polar and Cartesian Coordinates, but here is a quick summary:

From Polar Coordinates (r,θ)
to Cartesian Coordinates (x,y)
From Cartesian Coordinates (x,y)
to Polar Coordinates (r,θ)
  • x = r × cos( θ )
  • y = r × sin( θ )
  • r = √ ( x2 + y)
  • θ = tan-1 ( y / x )

An Example

Sam and Alex are pulling a box.
  • Sam pulls with 200 Newtons of force at 60°
  • Alex pulls with 120 Newtons of force at 45° as shown
What is the combined force, and its direction?



Let us add the two vectors head to tail:
Now, convert from polar to Cartesian (to 2 decimals):
Sam's Vector:
  • x = r × cos( θ ) = 200 × cos(60°) = 200 × 0.5 = 100
  • y = r × sin( θ ) = 200 × sin(60°) = 200 × 0.8660 = 173.21
Alex's Vector:
  • x = r × cos( θ ) = 120 × cos(-45°) = 120 × 0.7071 = 84.85
  • y = r × sin( θ ) = 120 × sin(-45°) = 120 × -0.7071 = -84.85
Now we have:

Now it is easy to add them:
(100, 173.21) + (84.85, -84.85) = (184.85, 88.36)
We can convert that to polar for a final answer:
  • r = √ ( x2 + y) = √ ( 184.852 + 88.36) = 204.88
  • θ = tan-1 ( y / x ) = tan-1 ( 88.36 / 184.85 ) = 25.5°

( I had this knowledge from the website :  http://www.mathsisfun.com/algebra/vectors.html )

When I had searched the vectors on the internet, I saw lots of web site and lots of knowledge about the subject.I have wanted  to choose best one for high school students.In my opinion, this lecture and visuals, pictures are clear and simple.I hope, when a high school student read my blog, he or she could have enough knowledge about the vectors.
Now, I want to talk about the history of vectors .


The parallelogram law for the addition of vectors is so intuitive that its origin is unknown. It may have appeared in a now lost work of Aristotle  (384--322 B.C.), and it is in the Mechanics of Heron (first century A.D.) of Alexandria.  It was also the first corollary in Isaac Newton's (1642--1727) Principia Mathematica (1687). In the Principia, Newton dealt extensively with what are now considered vectorial entities (e.g., velocity, force), but never the concept of a vector. The systematic study and use of vectors were a 19th and early 20th century phenomenon

Vectors were born in the first two decades of the 19th century with the geometric representations of complex numbers.  Caspar Wessel (1745--1818), Jean Robert Argand (1768--1822),Carl Friedrich Gauss (1777--1855), and at least one or two others conceived of complex numbers as points in the two-dimensional plane, i.e., as two-dimensional vectors.  Mathematicians and scientists worked with and applied these new numbers in various ways; for example, Gauss made crucial use of complex numbers to prove the Fundamental Theorem of Algebra (1799).  In 1837, William Rowan Hamilton (1805-1865) showed that the complex numbers could be considered abstractly as ordered pairs (ab) of real numbers. This idea was a part of the campaign of many mathematicians, including Hamilton himself, to search for a way to extend the two-dimensional "numbers" to three dimensions; but no one was able to accomplish this, while preserving the basic algebraic properties of real and complex numbers

In 1827, August Ferdinand Möbius published a short book, The Barycentric Calculus, in which he introduced directed line segments that he denoted by letters of the alphabet, vectors in all but the name. In his study of centers of gravity and projective geometry, Möbius developed an arithmetic of these directed line segments; he added them and he showed how to multiply them by a real number. His interests were elsewhere, however, and no one else bothered to notice the importance of these computations.

After a good deal of frustration, Hamilton was finally inspired to give up the search for such a three-dimensional "number" system and instead he invented a four-dimensional system that he called quaternions.

Hamilton had been knighted in 1835, and he was a well-known scientist who had done fundamental work in optics and theoretical physics by the time he invented quaternions, so they were given immediate recognition. In turn, he devoted the remaining 22 years of his life to their development and promotion. He wrote two exhaustive books, Lectures on Quaternions (1853) andElements of Quaternions (1866), detailing not just the algebra of quaternions but also how they could be used in geometry. At one point, Hamilton wrote, "I still must assert that this discovery appears to me to be as important for the middle of the nineteenth century as the discovery of fluxions was for the close of the seventeenth." He acquired a disciple, Peter Guthrie Tait (1831--1901), who in the 1850s began applying quaternions to problems in electricity and magnetism and to other problems in physics. In the second half of the 19th century, Tait’s advocacy of quaternions produced strong reactions, both positive and negative, in the scientific community.

At about the same time that Hamilton discovered quaternions, Hermann Grassmann (1809--1877) was composing The Calculus of Extension (1844), now well known by its German title,Ausdehnungslehre.  In 1832, Grassmann began development of "a new geometric calculus" as part of his study of the theory of tides, and he subsequently used these tools to simplify portions of two classical works, the Analytical Mechanics of Joseph Louis Lagrange (1736-1813) and the Celestial Mechanics of Pierre Simon Laplace (1749-1827).  In hisAusdehnungslehre, first, Grassmann expanded the conception of vectors from the familiar two or three dimensions to an arbitrary number, n, of dimensions; this greatly extended the ideas of space.  Second, and even more generally, Grassmann anticipated a good deal of modern matrix and linear algebra and vector and tensor analysis.

During the middle of the nineteenth century, Benjamin Peirce (1809--1880) was far and away the most prominent mathematician in the United States, and he referred to Hamilton as, "the monumental author of quaternions."  Peirce was a professor of mathematics and astronomy at Harvard from 1833 to 1880, and he wrote a massive System of Analytical Mechanics (1855; second edition 1872), in which, surprisingly, he did not include quaternions.  Rather, Peirce expanded on what he called "this wonderful algebra of space" in composing his Linear Associative Algebra (1870), a work of totally abstract algebra. Reportedly, quaternions had been Peirce’s favorite subject, and he had several students who went on to become mathematicians and who wrote a good number of books and papers on the subject.

James Clerk Maxwell (1831--1879) was a discerning and critical proponent of quaternions.  Maxwell and Tait were Scottish and had studied together in Edinburgh and at Cambridge University, and they shared interests in mathematical physics. In what he called "the mathematical classification of physical quantities," Maxwell divided the variables of physics into two categories, scalars and vectors. Then, in terms of this stratification, he pointed out that using quaternions made transparent the mathematical analogies in physics that had been discovered by Lord Kelvin (Sir William Thomson, 1824--1907) between the flow of heat and the distribution of electrostatic forces. However, in his papers, and especially in his very influential Treatise on Electricity and Magnetism (1873), Maxwell emphasized the importance of what he described as "quaternion ideas … or the doctrine of Vectors" as a "mathematical method … a method of thinking." At the same time, he pointed out the inhomogeneous nature of the product of quaternions, and he warned scientists away from using "quaternion methods" with its details involving the three vector components. Essentially, Maxwell was suggesting a purely vectorial analysis.

William Kingdon Clifford (1845--1879) expressed "profound admiration" for Grassmann’s Ausdehnungslehre and clearly favored vectors, which he often called steps, over quaternions. In his Elements of Dynamic (1878), Clifford broke down the product of two quaternions into two very different vector products, which he called the scalar product (now known as the dot product) and the vector product (today we call it the cross product).  For vector analysis, he asserted "[M]y conviction [is] that its principles will exert a vast influence upon the future of mathematical science."  Though the Elements of Dynamic was supposed to have been the first of a sequence of textbooks, Clifford never had the opportunity to pursue these ideas because he died quite young.

The development of the algebra of vectors and of vector analysis as we know it today was first revealed in sets of remarkable notes made by J. Willard Gibbs (1839--1903) for his students at Yale University.  Gibbs was a native of New Haven, Connecticut (his father had also been a professor at Yale), and his main scientific accomplishments were in physics, namely thermodynamics. Maxwell strongly supported Gibbs’s work in thermodynamics, especially the geometric presentations of Gibbs’s results. Gibbs was introduced to quaternions when he read Maxwell’s Treatise on Electricity and Magnetism, and Gibbs also studied Grassmann’s Ausdehnungslehre.  He concluded that vectors would provide a more efficient tool for his work in physics.  So, beginning in 1881, Gibbs privately printed notes on vector analysis for his students, which were widely distributed to scholars in the United States, Britain, and Europe.  The first book on modern vector analysis in English was Vector Analysis (1901), Gibbs’s notes as assembled by one of his last graduate students, Edwin B. Wilson (1879--1964).  Ironically, Wilson received his undergraduate education at Harvard (B.A. 1899) where he had learned about quaternions from his professor, James Mills Peirce (1834--1906), one of Benjamin Peirce’s sons.  The Gibbs/Wilson book was reprinted in a paperback edition in 1960.  Another contribution to the modern understanding and use of vectors was made by Jean Frenet (1816--1990). Frenet entered École normale supérieure in 1840, then studied at Toulouse where he wrote his doctoral thesis in 1847.  Frenet's thesis contains the theory of space curves and contains the formulas known as the Frenet-Serret formulas (the TNB frame).  Frenet gave only six formulas while Serret gave nine.  Frenet published this information in the Journal de mathematique pures et appliques in 1852. 

In the 1890s and the first decade of the twentieth century, Tait and a few others derided vectors and defended quaternions while numerous other scienitists and mathematicians designed their own vector methods.  Oliver Heaviside (1850--1925), a self-educated physicist who was greatly influenced by Maxwell, published papers and his Electromagnetic Theory (three volumes, 1893, 1899, 1912) in which he attacked quaternions and developed his own vector analysis. Heaviside had received copies of Gibbs’s notes and he spoke very highly of them. In introducing Maxwell’s theories of electricity and magnetism into Germany (1894), vector methods were advocated and several books on vector analysis in German followed.  Vector methods were introduced into Italy (1887, 1888, 1897), Russia (1907), and the Netherlands (1903).  Vectors are now the modern language of a great deal of physics and applied mathematics and they continue to hold their own intrinsic mathematical interest.
It is the developmental process of the vectors.Which work had been started by Aristotale, today it is in every system of technological equipments in our daily life.Maybe, this lecture is so long and boring for high school student but OUR INSTRUCTOR OGUZHAN DOGAN is interested in this history very very much, I am sure :)) I saw this lecture on this web site 
http://www.math.mcgill.ca/~labute/courses/133f03/VectorHistory.html If you like reading history and mathematics, you can look this website.And also you can get into the magic of history and mathematics.

If you are not an OGUZHAN DOGAN :)) and this blog is long for you, also you want to learn the vectors, this video may be ideal for you :)




I hope, this blog will be beneficial for high school students and sufficient for Oguzhan Hocamm :) 

See you later ;)

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