Solid mechanics deals with the study of the behavior of materials regarding their motion and physical deformation with the application of forces and other physical factors.
Before going
into the detailed study, one should know the basic terminologies regarding
solid mechanics.
Basic Terminologies
In the field of
engineering, solid mechanics involve basically Newtonian mechanics and it is
also known as Engineering Mechanics.
The following
are the terms basic to the study of mechanics:
Mass
Mass is considered as a fundamental quantity. By
definition, it is the measure of the quantity stored or possessed by a body.
The definition of matter says that any object that has mass and occupies space
is matter. So, mass is possessed by every matter. Mass is an extensive property
i.e. it depends on the size of the body. Mass of a body will change only if
some part of the body is physically separated.
SI unit of mass
is Kg. The standard value of 1 kg is equal to the mass of cylinder made of
platinum-iridium alloy kept at the International Bureau of Weights and Measures.
Time
Time is the measure of the interval between two successive events.
SI unit of time is second. The standard value 1 second is equal to the duration interval of 9192631770 periods of radiation of the cesium-133 atom.
Length
Length is the measure of linear distances.
SI unit of
length is meter. The standard value of 1 meter is equal to the distance
traveled by light in a vacuum in 1/299,792,458 second which is equal to the
1690763.73 wavelength of the krypton-86 atom. Also, 1 meter length of a cylinder of
platinum-iridium alloy kept at the Standard Bureau of Weights and Measures.
Space
Space is the geometric region in which a body is subjected to study.
Any point in space is measured by coordinates and angles. If the point is measured by perpendicular distances from mutually perpendicular axis then the measuring system is known as the Cartesian system. And, if the point is measured by radial distance and angle then the system is known as Polar coordinates.
Particle
A particle is defined as an object with mass but no dimension. Theoretically, such an object does not exist. But, when the distance between two objects is very large, compared to their size, then, the objects can be considered as a particle.
Rigid body
A body consists of many small particles held together by electrostatic forces. Since we are studying Newtonian mechanics; we will not go into the physics of electrostatic forces.
A rigid body is a body, in which the relative
position of the particles does not change with the application of forces.
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| P1: A rigid Body |
The Picture P1 shows a rigid body with the particles A, B, C.
A force is
applied to the body.
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| P2: After the application of force |
Force
You might have studied that a pull or push is known
as force. Yes, it is the simplest definition of force. Force can also be defined
as the external agency that changes or tends to change the state of rest or
motion of a body. This definition comes from Newton’s first law of motion.
For better understanding, you may consider that
something that pulls or pushed a body or tends to pull or push is known as
force.
The SI unit of force is Newton. 1 Newton force is
defined as the force that displaces a body of 1 kg through 1 m.
The quantity of force is given by Newton in his
second law of motion. It states that the quantity of force is proportional to
the product of mass and rate of change of velocity.
Since the rate of change of velocity is known as
acceleration therefore, force is equal to the mass times acceleration.
F=m*a
Scalar and Vector Quantity
Certain quantities in physics can be understood
completely by the numerical value and its unit but certain quantities need
other specifications (i.e. direction) to understand. For example, let’s say, a
car is moving with a speed of 30 kmph. The statement completely mentions the
numerical value of speed and its unit but it fails to mention the direction as
in which direction the car is moving. By giving the direction of the motion of the car, one completely understands the motion of the car. Now, let’s say, a
body has a mass of 2 kg. This statement provides the numerical value and unit
of mass and one can understand it clearly because there is no more data required to understand the mass. Let’s take
another example; a force of 20 N is applied to a body.
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| P3 |
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| P4 |
Hence, any quantity which requires only numerical value and its unit to express itself is known as scalar quantity whereas if the quantity also needs direction along with its numerical value and unit then, the quantity is said to be a vector quantity.
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