statics math
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Statics (ENGR 2214)Prof. S. Nasseri
What you need to know from Math!GEN 240
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Statics (ENGR 2214)Prof. S. Nasseri
Part 1
Preliminary
(Algebra, Geometry, Trigonometry)
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Statics (ENGR 2214)Prof. S. Nasseri
sin(0) 0, cos(0) 1, tan(0) 0
sin(90) 1, cos(90) 0, tan(90)
sin(180) 0, cos(180) 1, tan(180) 0sin(270) 1, cos(270) 0, tan(270)
1 3 3sin(30) cos(60) , cos(30) sin(60) , tan(30) , tan(60
2 2 3
! ! !
! ! ! g
! ! !! ! ! g
! ! ! ! ! ) 3
2
sin(45) cos(45) , tan(45) 12
!
! ! !
P ythagorean Theorem2 2 2
sin bsin , cos , tan =
cos a
a b c
b a
c c
UU U U
U
!
! ! !
a
bc
Usin
cos
tan
0
1
0
0
-1
�
1
0
�
-1
0
-�
sin
cos
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Statics (ENGR 2214)Prof. S. Nasseri
P ythagorean Theoremsin(0) 0, cos(0) 1, tan(0) 0
sin(90) 1, cos(90) 0, tan(90)
sin(180) 0, cos(180) 1, tan(180) 0
sin(270) 1, cos(270) 0, tan(270)1 3 3
sin(30) cos(60) , cos(30) sin(60) , tan(30) , tan(602 2 3
! ! !
! ! ! g
! ! !
! ! ! g
! ! ! ! ! ) 3
2sin(45) cos(45) , tan(45) 1
2
!
! ! !
hypotenuse
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Statics (ENGR 2214)Prof. S. Nasseri
P ythagorean Theorem
2 2
Law of sines:sin sin sin
Law of cosines: 2 cos
a b c
c a b ab
E F K
K
! !
! a
b
c
F
E
K
a
b
c
K
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Statics (ENGR 2214)Prof. S. Nasseri
The unit circle andtrigonometric functions
sin( ) sin , cos( ) cos , tan( ) tan
sin(180 ) sin , cos(180 ) cos , tan(180 ) tan
sin(180 )
(4th quadrant)
(2nd quadrant)
(3rd qsin , cos(180 ) cos , tan(180 ) tan uadrant
U U U U U U
U U U U U U
U U U U U U
! ! !
! ! !
! ! !sin(90 ) cos , cos(90 ) sin
s
)
(1st quadrant)
(2nd quadr in(90 ) cos , cos an(90 ) sin t)
U U U U
U U U U
! !
! !
+
+
+
-
-
-
-
+
c os
sin
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Statics (ENGR 2214)Prof. S. Nasseri
Double- & two-angle relations
2 2 2 2
2
sin(2 ) 2sin cos
cos(2 ) 1cos(2 ) cos sin 2cos 1 so: cos
2
2tantan(2 )
1 tan
U U U
UU U U U U
UU
U
!
¨ ¸! ! !© ¹
ª º
!
Two angle relations:
Double angle relations:
sin sin cos cos sincos cos cos sin sin
tan tantan
1 tan tan
E F E F E FE F E F E F
E FE F
E F
s ! ss !
ss !
m
m
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Statics (ENGR 2214)Prof. S. Nasseri
Arcs and sectors
2 2
Arc ength,
Angle measured in radians, / arc length/radius
1Sector area2 2
s r
s r
r r
U
U
U T UT
!
!
¨ ¸!© ¹ª º
r s
U
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Statics (ENGR 2214)Prof. S. Nasseri
Similar trianglesThe sides of two similar triangles are proportional and the angels are thesame. The respective heights of these triangles are also proportional to thesides.
a b c hd e f H
! ! !
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Statics (ENGR 2214)Prof. S. Nasseri
Part 2
Vectors
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Scalar: A quantity like mass or temperature, which only has amagnitude.Vector: A quantity like heat flux or force which has both amagnitude and a direction; denoted by a bold faced character (a),an underlined character (a), or a character with an arrow on it:
Vectors
ar
F
Fx
Fy
i
j
x
y
U
Resolution of a Vector: A vectorcan be resolved along differentdirections using the parallelogramrule. The figure shows how oneresolves vector F into componentsF x and F y which are along thegiven directions (i and j are theunit vectors; vectors of unitlength).
2 2
tan
x y
x y
y
x
F F
F F
F
F U
!
!
!
F i j
F
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Statics (ENGR 2214)Prof. S. Nasseri
Vector additionAddition follows the parallelogram law described in the figure.
x x y y F E F E ! F E i j
F
Fx
Fy
x
y
EEy
Ex
F+E
E
FE+F
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Statics (ENGR 2214)Prof. S. Nasseri
Part 3
Dot Product, Cross Product and
Triple Product
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Statics (ENGR 2214)Prof. S. Nasseri
Dot product
The dot product of two vectors yields a scalar:
C ! A . B
Magnitude:
cosC AB U!
A
B
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Statics (ENGR 2214)Prof. S. Nasseri
Right handed system of coordinates
thumb
indexmiddle
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Statics (ENGR 2214)Prof. S. Nasseri
Cross productThe cross product of two vectors yields a vector:
v ! A B C
Magnitude:
sinC AB U!
Direction:Vector C has a direction
perpendicular to the plane containingA and B such that C is specified bythe right hand rule.
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Statics (ENGR 2214)Prof. S. Nasseri
Cross productLaws of operations:The Commutative Law is Not Valid:
v { v A B B A
v v A B = -B A
Multiplication by a scalar:
a a a av ! v v ! v A B A B = A B A B
The Distributive Law:
v ! v v A B + D A B A D
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Statics (ENGR 2214)Prof. S. Nasseri
Cross products of unit vectorsThe direction is determined using the right hand rule. As shown in thediagram, for this case the direction is k and the Magnitude is:
| i v j |=(1)(1)(sin90 °) = (1)( 1)( 1) =1so: i v j = ( 1) k = k
and: i v j = k i v k = - j i v i = 0 j v k = i j v i = -k j v j = 0 k v i = j k v j = -i k v k = 0
alphabeti c al order +
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Statics (ENGR 2214)Prof. S. Nasseri
Cross product of two vectors
Cross product of two vectors in terms of their components:
A = Axi + Ay j +Az k
B = B xi + B y j + B z k
A v B = (Axi + Ay j + Az k ) v ( B xi + B y j + B z k )
= AxB x ( i v i) + AxB y ( i v j ) + AxB z ( i v k ) + Ay B x ( j v i) + Ay B y ( j v j ) + Ay B z ( j v k ) + Az B x ( k v i) + Az B y ( k v j ) + Az B z ( k v k )
= 0 + AxB y k ² AxB z j - Ay B x k + 0 + Ay B z i + Az B x j ² Az B y i + 0
Hen c e: A v B = (Ay B z ² Az B y ) i - (AxB z -Az B x) j + (AxB y - Ay B x ) k
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Statics (ENGR 2214)Prof. S. Nasseri
Cross product of two vectorsThis equation may also be written in a compact determinant form:
x y z
x y z
A A A
B B B
v
i j k
A B =
For element i: ( i )(A y B z ± A z B y )
z y x
z y x
B B B
A A A
k j
BA !v
z y x
z y x
k j
BA !v
For element j: (- j )(A B z -A z B )
(notice the negative sign
here) z¡ ¢
z¡ ¢
B B B
A A A
k ji
!v
z£ ¤
z£ ¤
B B B
A A A
k ji
!v
For element k : ( k )(A¥ B y - A y B¥ )
¦ y§
¦
y§
B B B
A A A
k ji
BA !v
z y x
z y x
B B B
A A A
k ji
BA !v
Hence:
A v B = ( A y B z ± A z B y ) i - ( A x B z - A z B x ) j + ( A x B y - A y B x ) k
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Statics (ENGR 2214)Prof. S. Nasseri
Cross product of two vectors
m
In summary, The cross product of vectors a and b is a vector perpendicularto both a and b and has a magnitude equal to area of the parallelogramgenerated from a and b .
The direction of the cross product is given by the right hand rule (fingers
from vector a to vector b and thumb is along vector c ). Order is important inthe cross product:
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Statics (ENGR 2214)Prof. S. Nasseri
Cross product of two vectors
( , and are the unit vectors)
Area sin
hich is the unit vector along the line perpendicular to the p
x y z
x y z
x y z y z z y x z z x x y y x
x y z
a a a
b b b
a a a a b a b a b a b a b a b ab
b b b
U
v ! v
!
!
v ! ! !
a b b a
a i j k i j k
b i j k
i j k
a b = i j k m m
m lane o anda b
m
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Statics (ENGR 2214)Prof. S. Nasseri
Triple product
.
x y z x y z
x y z x y z y z z y x x z z x y x y y x z
x y z x y y
a a a a a a
b b b b b b b c b c a b c b c a b c b c a
c c c c c c
® ! ±
! v ! ¯± ! °
a i j k
b i j k a b c =
c i j k
The volume of the parallelepiped constructed from the vectors a , b , and c is given bythe triple product of the three vectors:
volume sin cos
. cos
abc
a
U N
N
!
v ! va b c b c
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Statics (ENGR 2214)Prof. S. Nasseri
Part 4
D
ifferentiation,I
ntegration andCentroids
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Statics (ENGR 2214)Prof. S. Nasseri
Differentiation (common derivatives)d/d
x( c )= 0The der ivative of a constant is zer o.
Example: d(7) /dx = 0
d/dx( c × x )= c
The r ate of change of a linear function is its slope.
Example: d(3 × x ) /dx = 3
d/dx (xn) = n × x(n-1)
Example: d( x 4 )/dx = 4× x 3
d/dx (log x) = 1/x
The der ivative of the log of x is its inver se.
Example: d ( log ( x + 1) ) /dx = 1 / ( x + 1)
d/dx (eax) = a eax
Example: d (e3x ) /dx= 3 e3x
d/dx (sin cx) = c cos x
Example: d ( sin3x ) /dx = 3cos x
d/dx (cos x) = -sin x
Example: d ( cos t)= -sin t
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Statics (ENGR 2214)Prof. S. Nasseri
Integral of a function
The integral of a functionf( x) over an interval fromx1 to x2 yield the areaunder the curve in this
interval.
Note: The integral represents the
( ) F x x(§ as 0 x( p
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Statics (ENGR 2214)Prof. S. Nasseri
Some indefinite integrals to remember
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Statics (ENGR 2214)Prof. S. Nasseri
Some indefinite integrals to remember
Note: Remember to add a constant of integration if you are not specifyinglimits. You evaluate the constant of integration by forcing the integral topass through a known point.
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Statics (ENGR 2214)Prof. S. Nasseri
Definite integralNote: For definite integrals subtract the value of the integral atthe lower limit from its value at the upper limit. For example, if
you have the indefinite integral.Note: The following notation is common:
2
12 1( ) ( ) ( )
x x
x x F x F x F x!
! !
Integration by parts:
U dV U V Vd U ! ´ ´
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Statics (ENGR 2214)Prof. S. Nasseri
Centroid of an area
The centroid of an area is the area weighted average location of thegiven area.
1 1 1,
OC OC OC
OC OC OC
A A A
x y
x y
d A x xd A y r d A A A A
!
!
! ! !´ ´ ´
r i j
r i j
r r
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Statics (ENGR 2214)Prof. S. Nasseri
Centroid of an areaFor example, consider a shape that is a composite of n individual segments,each segment having an area Ai and coordinates of its centroid as xi and y i.The coordinates of the centroid of this composite shape is given by