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Mechanics
This section will cover the basics of mechanics. Mechanics is a branch of Physical Science dealing with the study of energy and force, and their relation to the equilibrium, or motion of solids, fluids and gases.
Newton's Laws of Motion
First Law: If a body is at rest it will remain at rest until a force acts upon it. If an object is moving in a straight line at a constant speed it will continue to do so until a force acts upon it.
Second Law: Acceleration (a) of a moving body is directly proportional to the force (F) and inversely proportional to the mass (m) of tge body. F = m x a.
Third Law: The action of a force upon a body at rest is equal to an opposite force-reaction (static).
Force and Motion
Force is any action placed on a body that makes it move, changes its motion, or changes its size. Motion is the act, process, or instance of changing place.
A force is a vector quantity characterized by both magnitude and direction. Forces are represented graphically by a line with an arrowhead at one end. The length of the line represents the magnitude of the force, the arrowhead represents its direction, and the end opposite the arrowhead represents the forces application.
The magnitude of a force may be expressed in different units. Commonly used units are,
dyne: the force required to accelerate a mass of one gram at a rate of one centimeter per second squared.
kilogram-force (kgf): the force exerted by one kilogram of mass in standard Earth gravity.
newton: the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second squared.
pound-force (lbf or lb-f): The pound-force is equal to a mass of one pound multiplied by the standard acceleration of gravity.
FORCE |
dyne |
kgf |
N |
lb-f |
1 dyne |
1 |
1.020 x 10ˉ 6 |
10ˉ |
7.233 x 10ˉ |
1 kilogram | 9.807 x 10 | 1 | 9.807 | 2.205 |
1 newton | 10 | 0.1020 | 1 | .2248 |
1 pound | 4.448 x 10 | .4536 | 4.448 | 1 |
Most practical problems related to forces include two or more forces acting simultaneously upon a body. Any two or more forces (f1, f2, f3,....fn) may be replaced by a sin