Upload
maximilian-long
View
260
Download
3
Tags:
Embed Size (px)
Citation preview
Chapter Two
Laith Batarseh
Statics
FORCE VECTORS
By
Statics
FORCE VECTORS
Definition
Engineering mechanics
Deformable body mechanics
Rigid body mechanics
Dynamics Statics
Fluid mechanics
Constant Velocity Variable
Velocity
Statics
FORCE VECTORS
Definition
Rigid body is the body that has the same volume parameters before and after applying the load
Deformable body is the body changes its volume parameters when the load is applied on it.
Statics
FORCE VECTORS
Definition
Static Cases:
Dynamic Case:
Velocity = 0P
BA
PVelocity = Constant
BA
PVelocity is changeable
Acceleration or Deceleration
Statics
FORCE VECTORS
Definition
P
At rest Acceleration Deceleration Constant velocity
Dynamics Statics
EndStart
Statics
FORCE VECTORS
Cartesian coordinate system
x
y
x
y
z
y-z plane
x-y plane x-
z pl
ane
x-y plane x-y plane
Statics
FORCE VECTORS
Definition
x
y
y
P(x,y)
Statics
FORCE VECTORS
Newtown's Laws of Motion
Newtown's Laws of Motion
First Law: a particle at rest or moves in constant velocity will remain on its state unless it is subjected to unbalance force.
F1 F4
F3 F2
0 F
F
Second Law: a particle subjected to unbalance force will move at acceleration has the same direction of the force.
maF
Third Law: each acting force has a reaction equal in magnitude and opposite in direction
AAction: Force of A acting on B B Reaction: Force of B acting on A
Statics
FORCE VECTORS
Newtown's Law of Gravity
Newtown proved his most famous law at all in the 17th centaury and called it Law of Universal Gravitation.
Statement: any two objects have a masses (M1 and M2 )and far away from each other by a distance (R) will have attraction force (gravitational) related proportionally with the objects masses product (M1 M2 ) and inversely with the square of the distance between them (R2). Mathematically:
Where: G = 66.73 x 10-12 m3/(kg.s2)Weight: according to Newtown's Law of Gravity, weight is the gravitational force acting between the body has a mass (m) and the earth (of mass Me) and is given as: W=mg. g is the gravitational acceleration and equal to GMe/R2.
constant isG ;2
21
R
MMGF
Statics
FORCE VECTORS
Units of Measurements
According to Newton's 2nd law, the unit of force is a combination of the other three quantities: mass, length and time. So, the force units N (Newtown) and lbf can be written as:
22 .
s
ftlbmlbfand
s
mkgN
Units of Measurements Lengt
h(m or
ft)
Mass(kg or lbm)
Time(sec)
Force(N or lbf)
SImKgN
Englishft
lbmlbf
Statics
FORCE VECTORS
Scalar versus vectors
Physical Quantity
Scalar Vector
Is any physical quantity can be described fully by a magnitude
only.
Is any physical quantity needs both magnitude and direction
to be fully described.
Examples: mass, length and time.
Examples: force, position and moment.
Statics
FORCE VECTORS
Scalar versus vectors
Direction (θ)
Magnitude (M)
Sense of Direction
Fixed axis
Vector
30o
5 units
This vector has a magnitude of 5 units and it tilted from the horizontal axis by +30o
Example
Vector notations:1. A2. 3. V = M∟θ
A
Sense of Direction
Statics
FORCE VECTORS
Vector operations
A
2A
0.5A-A
Multiplication by a scalar
30o
A=5∟30o
2A =10∟30o 0.5A =2.5∟30o -A =-5∟30o = 5∟180+30o
Example
Statics
FORCE VECTORS
Vector operations
A
Vector addition (A+B) Vector subtraction (A-B)
B
R=A+B
A
B
R=A+B
A
B
A
-B
R=A-BA
-B
R=A-BA
-BOR
Statics
FORCE VECTORS
Vector operations
Example:Assume the following vectors: A = 10∟30o and B = 7∟-20 o
Find: 1. A+B2. A-B
Solution:
A+B
AB
A-B A
-B
Statics
FORCE VECTORS
Vector operations
Special cases:Collinear vectors:
Multiple addition:
A+B+C+…: in such case, the addition can be in successive order or in multiple steps.
A BA + B
A + B
B - AA B
B-A
Statics
FORCE VECTORS
Vector operations
Example:Assume the following vectors: A = 10∟30o ,B = 7∟-20 o and C = 6∟135o . Find: A+B+(A+C)
Solution:
A+B
A+CAB
C
A
A+B+(A+C)
A+B
A+C
Statics
FORCE VECTORS
Vector operations
Example (cont): Find A+B+(A-C)
A+B
AB A+B
AA+B+A
A+B+A-C
-C
A+B+A
FORCE VECTORS
Examples
FORCE VECTORS
Examples
FORCE VECTORS
Examples
FORCE VECTORS
Examples
FORCE VECTORS
Coplanar forces
Coplanar forcesCoplanar forces are the forces that share the same plane.These forces can be represented by their components on x and y axes which are called the rectangular components.The components can be represented by scalar and Cartesian notations.Scalar notation
Cartesian notation
Fx = F cos(θ)y
x
Fy
Fx
F
θ
Fy= F sin(θ)
Fy
Fx
F
xi
yj F = Fx i + Fy j
FORCE VECTORS
Scalar notation cases
y
x
Fy
Fx
F
θ
Fx = F cos(θ)
Fy= F sin(θ)
1 2
y
xFy
Fx
c
Fx /F= a/c
Fy /F= b/c
abF
FORCE VECTORS
Scalar notation cases
Cartesian notation cases
Fy
Fx
F
xi
yj F2,y
F2
F2,x
F1,y
F1
F1,x
F4,xF4
F4,y
x
y
F3,x
F3,y
F3
F 1= F1,x i + F1,y j
F 2 = -F2,x i + F2,y j
F 3= -F3,x i - F3,y j F 4= F4,x i - F4,y j
FORCE VECTORS
Force summation
For both cases of notations, the magnitude of the resultant force is found by:
And the direction is found by:
FR,x =∑Fx
FR,y =∑Fy
2yR,
2xR,R FFF FR,y
FR,x
FR
θ
xR
yR
F
F
,
,1tan
+ve
+ve
FORCE VECTORS
Examples
FORCE VECTORS
Examples
FORCE VECTORS
Examples
FORCE VECTORS
Examples
Cartesian Vectors
Forces
Three dimensions
Two dimensions
One dimension
Cartesian Vectors
• In three dimensions system, new component appeared (Az).
• The new dimension direction is represented by unit vector (k)
• The position of the vector has to be located by three angles one from each axis
• The projection of vector on x-y plane represent a new vector
called A’
A
Az
z
y
x
Ax
Ay
A’
Note that
Cartesian Vectors
Right hand coordinate system• This method is used to
describe the rectangular coordinate system.
• The system is said to be right handed if the thumb points to the positive z-axis and the fingers are curled about this axis and points from the positive x-axis to the positive y-axis.
Cartesian Vectors
Notation • To find the components of a
vector oriented in three dimensions, two successive applications of the parallel-ogram must be done.
• One of the parallelogram applications is to resolve A to A’ and Az and the other is used to resolve A’ into Ax and Ay.
• A = A’ + Az = Ax + Ay + Az
A
Az
z
y
x
Ax
A y
A’
Cartesian VectorsAngles• α is the angle between the vector and x-axis• β is the angle between the vector and y-axis• γ is the angle between the vector and z-axis
α β
γ
Cartesian Vectors
Cartesian unit vectors k
j
i
A = Ax i + Ay j + Az k
Ax = Acos(α)Ay = Acos(β)Az = Acos(γ)
Cartesian Vectors
Magnitude and Direction
Magnitude
Direction
222zyx AAAA
A
AA
AA
A
z
y
x
cos
cos
cos
1coscoscos 222
FORCE VECTORS
Examples
FORCE VECTORS
Examples
FORCE VECTORS
FORCE VECTORS
FORCE VECTORS
FORCE VECTORS
FORCE VECTORS
Cartesian Vectors
Other direction definition
A = Ax i + Ay j + Az k
kjiuA
A
A
A
A
A
Azyx
A A
uA = cos(α) i + cos(β) j + cos(γ) k
A = |A| uA = |A| cos(α) i + |A| cos(β) j + |A| cos(γ) k = Ax i + Ay j + Az k
Cartesian Vectors
Other direction definition cont
Az = A cos(ϕ)
A’ = A sin(ϕ)
Ax = A’ cos(θ) = A sin(ϕ) cos(θ)Ay = A’ sin(θ) = A sin(ϕ) sin(θ)
θ
ϕ
Cartesian Vectors
Cartesian Vectors Addition
• A = Ax i + Ay j + Az k
• B = Bx i + By j + Bz k
• R = A+ B = (Ax + Bx ) i + (Ay + By) j +(Az + Bz ) k
General rule:FR = ∑F = ∑Fx i + ∑Fy j + ∑Fz k
Cartesian Vectors
Example [1]:Question: assume the following forces:
F1 = 5 i + 6j -4k
F2 = -3i +3j +3k
F3=7i-12j+2k
Find the resultant force F = F1 + F2 +F3 and represent it in both Cartesian and scalar notations
Solution:
Given: F1, F2 and F3
Required: find resultant force F and represent it in both Cartesian and scalar notation
Cartesian Vectors
Example [1]:
Solution: F = (5-3+7)i + (6+3-2)j +(-4+3+2)k = 9i +7j +10k (Cartesian notation)
Scalar notation:
Magnitude:
Unit vector u:
NF 17.151079 222
kjikjiF
u 66.046.06.015.17
10 7 9
F
7.48 66.0cos
61.62 46.0cos
13.53 6.0cos
o
o
o
Cartesian Vectors
Position vector
Assume: r = ai + bj + ck
• At this point, r is called position vector.• Position vector is a vector
locates a point in space with respect to other point.• in this case, vector r is a
position vector relates point P
to point O.
Cartesian Vectors
Position vector
• Assume vectors rA and rB are used to locate points A and B from the origin (ie. Point 0,0,0).
• Define a position vector r to relate point A to point B.
• rB = r + rA → r = rB – rA
• r = (xB – xA)i + (yB – yA)j + (zB – zA)k
FORCE VECTORS
End of Chapter Two