Mechanics 1 BSC 021 Lecture 1 PDF

Mechanics 1 BSC 021  Dr. Hewayda Elghawalby  CHAPTER 1 General Principles  CHAPTER OBJECTIVES to provide an introduction to the basic quantities and idealizations of mechanics. to give a statement of newton’s Laws of Motion. to review the principles for applying the SI system of...

Mechanics 1 BSC 021  Dr. Hewayda Elghawalby  CHAPTER 1 General Principles  CHAPTER OBJECTIVES to provide an introduction to the basic quantities and idealizations of mechanics. to give a statement of newton’s Laws of Motion. to review the principles for applying the SI system of units. to examine the standard procedures for performing numerical calculations.  CHAPTER OUTLINES Introduction. Fundamental Concepts. Units of Measurement. Numerical Calculations.  Introduction Mechanics is a branch of the physical sciences that is concerned with the state of rest or motion of bodies that are subjected to the action of forces. In general, this subject can be subdivided into three branches: rigid-body mechanics, deformable- body mechanics, and fluid mechanics.  Introduction In our course we will study rigid-body mechanics since it is a basic requirement for the study of the mechanics of deformable bodies and the mechanics of fluids. Furthermore, rigid-body mechanics is essential for the design and analysis of many types of structural members, mechanical components, or electrical devices encountered in engineering.  Rigid-body mechanics statics dynamics deals with the equilibrium of is concerned with the bodies, that is, those that are accelerated motion of either at rest or move with a bodies. constant velocity. Fundamental Concepts Basic Quantities. Idealizations. Newton’s Three Laws of Motion. Weight.  Fundamental Concepts Basic Quantities. Length. is used to locate the position of a point in space. Time. is conceived as a succession of events. Mass. is a measure of a quantity of matter that is used to compare the action of one body with that of another. Force. is considered as a “push” or “pull” exerted by one body on another.  Fundamental Concepts Idealizations. Particle. A particle has a mass, but a size that can be neglected. Rigid Body. A rigid body can be considered as a combination of a large number of particles in which all the particles remain at a fixed distance from one another, both before and after applying a load. Concentrated Force. A concentrated force represents the effect of a loading which is assumed to act at a point on a body.  Fundamental Concepts Newton’s Three Laws of Motion. First Law. A particle originally at rest, or moving in a straight line with constant velocity, tends to remain in this state provided the particle is not subjected to an unbalanced force.  Fundamental Concepts Newton’s Three Laws of Motion. Second Law. A particle acted upon by an unbalanced force F experiences an acceleration a that has the same direction as the force and a magnitude that is directly proportional to the force.  Fundamental Concepts Newton’s Three Laws of Motion. Third Law. The mutual forces of action and reaction between two particles are equal, opposite, and collinear.  Fundamental Concepts Weight. In the case of a particle located at or near the surface of the earth, the weight, the only gravitational force having any sizable magnitude. The weight W of a particle having a mass m, then we have that: Where, g is the acceleration due to gravity. Units of Measurement Length, mass, time, and other physical characteristics can be expressed in two basic systems of units: English and metric. Units of Measurement Many US scientists and engineers prefer the English system; it measures length in feet or inches, mass is slugs. force in pounds, time in seconds, and pressure in pounds per square inch. Units of Measurement There are two different versions of the metric system. The older version is the centimeter-gram-second (cgs) system. it measures length in centimeters, mass in grams, and time in seconds. The more modem version is the System International (SI) form of units. length is measured in meters, mass in kilograms, force in newtons, time in seconds, and pressure in pascals.  systems of units International System U.S. Customary of Units(SI) (FPS) Conversion of Units The following Table provides a set of direct conversion factors between FPS and SI units for the basic quantities. Also, in the FPS system, recall that 1 ft = 12 in. (inches), 5280 ft = 1 mi (mile), 1000 lb = 1 kip (kilo-pound), and 2000 lb = 1 ton.  Numerical Calculations Numerical work in engineering practice is most often performed by using handheld calculators and computers. It is important, however, that the answers to any problem be reported with justifiable accuracy using appropriate significant figures. Dimensional Homogeneity. Significant Figures. Rounding Off Numbers.