Transcript chapter one

EML 3004C
CHAPTER ONE
General Principles
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-1
EML 3004C
Statics, Dynamics and Mechanics of Materials
 Statics deals with the state of rest or motion of bodies with
constant velocities  F   M  0
 In dynamics, the bodies are allowed to accelerate.  F   M  ma
 Two Branches of static equilibrium
 Statics
 Mechanics of Materials
Statics
 Equilibrium of Bodies-material independent,
uses only static equations
Mechanics of Materials
F  M  0
 Relationship between the external loads, the
intensity of internal forces and its deformation
response
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-2
EML 3004C
Basic Concepts
 Quantities
 Length (location, position,
size)
 Time (succession of events)
 Force (Push, Pull)
 Mass (Properties of Matter)
 ONLY THREE OF FOUR
NEEDED (NEWTONS LAW)
Namas Chandra
Introduction to Mechanical engineering
 Idealization
 Particle (neglect, size,
geometry)
 Rigid Body (all points
within remain in the same
position, at fixed distances
from each other)
 Concentrated Force ( over
a very small area, zero)
Hibbler
Chapter 1-3
EML 3004C
Physical Quantities
 Physical Qualities
 Mass,
 Volume
 Force
 area
 time
 length
 distance,
 displacement
 Density
 velocity
 Temperature
 acceleration
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-4
EML 3004C
Scalar and Vector Quantities
 Scalar Quantities
Described by their magnitude, mass
(italic form) or lower case (a for A)
 Vector Quantities
Described by a magnitude, a direction, and a point of
application
(Bold Face) in the book
A,A
Bar or Arrow in handwritten work
A
Magnitude A or A (italic) or a =
R
R
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-5
EML 3004C
Newton’s Laws
 Newton’s First Law
 A body at rest tends to remain at rest & a body in motion at a
constant velocity will tend to maintain the velocity.
 Newton’s Second Law
 Change of motion is proportional to the moving force
impressed and takes place in the direction of the straight line
in which such force is impressed.
F  ma
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-6
EML 3004C
Newton’s Laws
 Consequences of Newton’s Third Law
 When two bodies interact, a pair of equal and opposite
reaction forces will exist at their contact point.
 This force pair will have the same magnitude and acts along
the same direction, but have opposite sense.
 The mutual force of action and reaction between two bodies
are equal, opposite, and collinear.
Kg = mass=[m] Newton = Force=[F]
Slug= mass =[m] lbf = Force = [F]
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-7
EML 3004C
Gravitational Law
 Gravitational Law
m1m2
F G 2
r
G = universal constant of gravitation
 66.73 10
12
m3
kg  s 2
m1,m2 = mass of each of the two particles
r= distance
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-8
EML 3004C
What is weight?
 Weight
If m1 = mass of the particle
m2 = mass of the earth
r
= distance of the particle to the earth’s center
W = weight of the particle
if
m1m2
W G 2
r
Gm2
g 2
r
Namas Chandra
Introduction to Mechanical engineering
W  mg
Hibbler
Chapter 1-9
EML 3004C
Units
 Units
Length, time, mass, force basic quantities
F  ma
 SI (International System of
Units)
Meter (m)
Second (sec)
Kilogram (kg)
Newton (N)
(Note: we use bars to denote forces or vectors)
Ex : mass = 1kg
W  mg
g  9.81 m s 2
Namas Chandra
Introduction to Mechanical engineering
 kg  m 
N  2 
 s 
W = 9.81N
Hibbler
Chapter 1-10
EML 3004C
Conversion of Units
 Conversion of Units
Force
Mass
Length
Ex:
2 kN
FPS
1 lb
1 slug
1 ft
=
=
=
SI
4.4482 N
14.5938 kg
0.3048 m
2kN  1000 N  1lb   0.3048m 




m
m  1kN  4.4482 N   1 ft 
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-11
EML 3004C
CHAPTER ONE.. concludes
General Principles
Namas Chandra
Introduction to Mechanical engineering
Hibbler
Chapter 1-12