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, deformation-body mechanics, and fluid mechanics.
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 fluid . Furthermore, rigid-body mechanics is essential for the design and analysis of many types of structural members and mechanical components .
Rigid-body mechanics is divided into two areas : statics and dynamics. Statics deals with the equilibrium of bodies , that is , those are either at rest or move with a constant velocity ; whereas dynamics is concerned with the accelerated motion of bodies.
Basic Quantities :
The following four quantities are used throughout mechanics.
Length :is used to locate the position of appoint in space and thereby describe the size of physical system .
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 . This interaction can occur when there is direct contact between the bodies, such as a person pushing on a wall , or it can occur through a distance when the bodies are physically separated.
Idealizations :
Models or idealizations are used mechanics in order to simplify application of the theory . Here we will consider three important idealizations :
Particle : a particle has a mass , but a size that can be neglected. When a body is idealized as a particle. The principles of mechanics reduce to a rather simplified from since the geometry of the body will not be involved in the analysis of the problem .
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. We can represent a load by a concentrated force .
Newton s Three Laws of Motion :
Engineering mechanics is formulated on the basis of Newton s three laws of motion. The validity of which is based on experimental observation . These laws apply to the motion of particle as measured from a nonaccelerating reference frame. They may be briefly stated as follows :
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.
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 . If F is applied to a particle of mass m , this law may be expressed mathematically as :
Third Law : the mutual forces of action and reaction between two particles are equal, opposite , and collinear .
Units of Measurement :
SI Units : the International System of units , is a modern version of the metric system which has received worldwide recognition. The SI system defines length in meters (m). time in seconds (s), and mass in kilograms (kg). The unit of force, called a newton (N) , is derived from F = ma. Thus, 1 Newton is equal to a force required to give 1 kilogram of mass an acceleration of 1 m/s2 (N = kg.m/s2) .
If the weight of a body located at the " standard location" is to be determined in Newton. Here measurements give g = 9.806 m/s2 :
W = mg (g = 9.806 m/s2)
U.S. Customary : in the U.S. Customary system of units (FPS) length is measured in feet (ft), time in second (s), and force in pounds (Ib) . The unit of mass, called a slug, is derived from F = ma .
Example :
Convert 2 km/h to m/s How many ft/s is this ?
Solution:
Since 1km = 1000 m and 1h = 3600 s , the factors of conversion are arranged in the following order, so that a cancellation of the units can be applied :
Example :
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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