lect_1_2
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engineering mechanicsTRANSCRIPT
ENGINEERING MECHANICS
JATIN PATELLECTURER,
SCHOOL OF PETROLEUM TECHNOLOGY, RAISAN, GANDHINAGAR
Course No.: ESH110T Course Title: Engineering MechanicsCredits: 7 credits (3 L +1 T)Faculty: Jatin Patel
Course contentsFundamental of Statics: • Principles of statics, coplanar, concurrent and
non-concurrent, parallel and non parallel forces, composition and resolution of forces, moments and couples-their properties. Combination of coplanar couples and forces, equilibrant, equilibrium, free body diagrams, analytical conditions of equilibrium of coplanar force systems.
Course contents…Truss: • Simple determinate plane trusses and analysis
for member forces using methods of joints and methods of sections..
Laws of friction: • Wedge, inclined plane, screw and screw jack,
Belt friction, collar friction
Course contents…Distributed forces, center of gravity and
moment of inertia: • Center of gravity of different sections used in
engineering, Moment of inertia of plane figures, polar moment of inertia, moment of inertia of rigid bodies, laminate and composite sections
Course contents…Virtual work and potential energy principles:
Application of these principles as replacement of equation of statics for real life problems
Kinetics of particles: D‟ Alembert‟s principle for translation and curvilinear motion, work and energy methods related to engineering systems, Linear motion, circular motion, rotation and translation, displacement, velocity and acceleration time diagrams.
Course contents…Vibrations:
Mechanical vibration of single degree of freedom system
• F.P. Beer and E.R. Johnston, Vector Mechanics for Engineers: Statics and Dynamics, Fifth edition, McGraw Hill.
• D.J. McGill and W.W. King, Engineering Mechanics: an Introduction to Dynamics, Third edition, PWS Publishing.
• J.L. Meriam and L.G. Kraige, Engineering Mechanics: Dynamics, Fourth edition, Wiley.
• W.F. Riley and L.D. Sturges, Engineering Mechanics: Dynamics, Second edition, Wiley.
• A. Bedford and W. Fowler, Engineering Mechanics: Dynamics, Addison-Wesley.
• S. B. Junarkar & H. J. Shah, Applied Mechanics, Charotar Publication
Recommended books:
InstructionsMinimum 80% attendance is necessary for the course.
20% includes all types of leaves.Absence in any examination (i.e. mid semester exam.,
end semester exam.) will be evaluated as zero mark for that particular examination irrespective of any reasons.
Evaluation
• Mid semester examination 40 %• End semester examination 60 %
Fundamentals of Engineering Mechanics
Imagine the following situations: (a) You have to design a car, which can run at a
speed of 140 km/hr on an expressway. In order to do this, you have to find engine power and the forces acting on the car body. Forces will come due to wind
resistance, rolling resistance and inertia.
(b) A nozzle issues a jet of water with a high velocity, which impinges upon the blades of turbine. The blades deflect the jet of water through an angle. You have to find out the force exerted by the jet upon the turbine.
To deal with above situations, you need to study ENGINEERING MECHANICS.
We study engineering mechanics to develop the capacity to predict the effects of force on motion while carrying out the creative design functions of engineering.
We can define mechanics as the physical science which deals with the effects of forces on objects.
• We shall follow continuum hypothesis while studying mechanics. A hypothetical continuous distribution of matter is called continuum.
This course will act as a foundation for fluid mechanics and solid mechanics courses. There, we deal with deformable bodies. In this course, we will be studying the behavior of rigid bodies under forces.
Rigid body: A body is considered rigid when the changes in distance between any two of its points is negligible in case of external force/pressure.The mechanics of rigid body:
(1) Statics (2) Dynamics
Deformable body: A body is considered deformable when the changes in distance between any two of its points cannot be neglected.
Some fundamental Definitions: • Space: It is a geometric region occupied by bodies
whose positions are described by linear and angular measurements relative to coordinate system.
• Time: It is a measure of the succession of events and is a basic quantity in dynamics.
• Force : Force is the action of one body on another. A force tends to move the body in the direction of its action. The action of a force is characterized by its magnitude, by the direction of its action and by its points of application.
• Particle: A particle is a body of negligible dimensions. Any element of a body may be treated as a particle when its dimensions are irrelevant to the description of its position or the action of forces applied on it.
• Scalar quantities : These are the quantities characterized by only magnitude, such as mass, temperature.
• Vector quantities : These are the quantities characterized by magnitude and direction, such as velocity, force. We will indicate vector quantities by boldfaced letters.
Concurrent forces: Two or more forces are said to be concurrent at a point if their lines of action intersect at that point. The below Fig. shows 3 concurrent forces.
Laws of Mechanics:
Newton's three laws form a part of foundation of mechanics. These are:
First law: Every object in a state of uniform motion tends to remain in that state motion unless an external force is applied to it.
This law is also called “law of inertia”.
Second law: The change of motion is proportional to the natural force impressed and is made in a direction of the straight line in which the force is impressed.
Mathematically, this law is stated as: F = m a
where F is the applied force, m is the mass and a is the acceleration.
Note, that force and acceleration are vectors and are indicated in boldface letters.
Third law : For every action, there is an equal and opposite reaction .
Law of gravitational attraction : Two particles will be attracted towards each other along their connecting line with a force whose magnitude is directly proportional to the product of the masses and inversely proportional to the distance squared between the particles.
where G is called the universal gravitational constant.
Parallelogram law: The forces could be combined by representing them by arrows to some suitable scale, and then forming a parallelogram in which the diagonal represents the sum of the two forces. In fact, all vectors must combine in this manner.
• For example if P and Q are two forces, the resultant R can be found by constructing the parallelogram.
Triangle law: If the two forces acting simultaneously on a body are represented by the sides of a triangle taken in order, then their resultant is represented by the closing side of the triangle in the opposite order.
Basic Quantities• Length, Mass, Time, Force
Units of Measurement
• m, kg, s, N… (SI, Int. System of Units)
Exercise
Ex:1 Show that the units MPa and N/mm2 are
numerically same.
Ex:2 Determine your weight in Newton.
Ex:3 From the gravitational law, calculate the
weight W of an 80-kg man in a space craft
travelling in a circular orbit 250 km above the
earth’s surface. Take G = 6.673X10-11 N.m2/kg2,
Earth radius, R=6.371x106 m and mass of the
earth, M=5.976x1024 kg
Ex:4 Compute the magnitude F of the force
which the sun exerts on the earth.
Perform the calculations in Newtons. Take G
= 6.673X10-11 N.m2/kg2, Earth radius,
R=6.371x106 m and mass of the earth,
M=5.976x1024 kg, mean distance between
earth and sun = 149.6x106 km, mean
diameter of the sun = 1392000 km