Engineering Mechanics

Lecture slides by

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Dr. Chandan Kumar

ASSO. PROFESSOR

GIET, BBSR

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Example: 1�Mechanical Engg.

• Use of statics in Robotics to build evil Terminator. (http://www.societyofrobots.com/mechanics_statics.shtml)

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Example 2�Civil Engg.

• The bridge should be capable of being in equilibrium while subject to self-load, wind-load etc

(http://oli.web.cmu.edu)

Example 3�Biomedical Engg.

• Force applying mechanisms are applied to bones for lengthening or removing deformities.

(http://oli.web.cmu.edu)

Example-4�Computer Engg.

• Hard-drives are complex mechanical systems. High magnetic forces are used to swivel recording head to required position. (http://oli.web.cmu.edu)

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Example-5�Seismology (natural phenomena)

• Earthquake results because of release of pent-up up energy between two sliding tectonic plates. (http://oli.web.cmu.edu)

What is Mechanics?

What’s the big deal with E. Mech?

• In principle, like cricket, it’s a simple game.
• Simply, force balance and moment balance.
• What is the need for an elaborate course?
• The basic rules are simple but there are many intricacies. Multi-body interactions can be very complex.
• A good understanding of fundamentals goes a long way in solving such complex problems.
• Concepts of appropriate Free Body Diagrams and equations of equilibrium (motion in dynamics) will be indispensable in later studies of mechanical engineering.

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Fundamental Principles

Newton’s Laws

Newton’s Laws

Newton’s third law on a lighter note

"for every action there is an equal and opposite reaction" and we shouldn't forget the laws of cause and effect, karma or whatever

http://www.kunama.com/personal/blog/2005/07/balance-of-nature.html

Systems of Units

• Kinetic Units: length, time, mass, and force.

• Three of the kinetic units, referred to as basic units, may be defined arbitrarily. The fourth unit, referred to as a derived unit, must have a definition compatible with Newton’s 2nd Law,

In this course we will predominantly use SI system of units. At times we may use imperial units (length:foot, mass:pound, time:second, force:pounds/kips.

Conversion of units can be easily done on your mobiles (not in class) or at:

http://www.onlineconversion.com/

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Modeling Real Life Problems

• Any physical/mechanical model is simple a caricature of a real-world problem.
• Such a model is our way of understanding of real-world in as simple and tractable way as possible.
• Allows us to calculate forces/etc., which can then be re-mapped to the real problem.
• The real skill is to remove unwanted flab, and get a bare-bones model, which gives a quick and reasonably accurate solution.

Example-1: Roof Truss

Another Example: Aircraft Landing Gear

Example 3�Bridge

http://oli.web.cmu.edu

Example 4�Simple basket-ball pole

http://oli.web.cmu.edu

Example-5�Ladder Climbing

http://oli.web.cmu.edu

Example-5�Draw-Bridge

Numerical Accuracy

• The accuracy of a solution depends on 1) accuracy of the given data, and 2) accuracy of the computations performed. The solution cannot be more accurate than the less accurate of these two.

• As a general rule for engineering problems, the data are seldom known with an accuracy greater than 0.2%. Therefore, it is usually appropriate to record parameters beginning with “1” with four digits and with three digits in all other cases, i.e., 40.2 N and 15.58 N.

• The use of hand calculators and computers generally makes the accuracy of the computations much greater than the accuracy of the data. Hence, the solution accuracy is usually limited by the data accuracy.