Page 63 - CITS - WCS - Mechanical

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The examples of motion include: running, cycling, jumping, swimming, eating, drinking, playing, writing,
typing, moving cars, throwing ball. The examples of rest include: sleeping, sitting, standing, staring, lying, a
fixed clock, bottle kept on a table, a stopped car.
Linear motion is any that moves along a straight line in one direction. The direction can either be horizontal
vertical or inclined direction. Example approach run. Angular motion is rotator motion it occurs when all points
on a body or object move in a circular path about the same fixed central line or axis.
Examples include the rotation of a bicycle tire, a merry-go-round, a toy top, a food processor, a laboratory
centrifuge, and the orbit of the Earth around the Sum an athlete running a 100-meter dash along a straight
track.
Force: Force can be defined as a push or a pull that changes or tends to change the state of rest or uniform
motion of an object or changes the direction or shape of an object. It causes objects to accelerate or add to
their overall pressure. The two main types of forces are contact and non-contact forces.
Some examples of force are Nuclear force, gravitational force, Frictional force, magnetic force, electrostatic
force, spring force and so on.
Units: Therefore, the unit of force is kg m/s2, which is what we refer to as Newton or N. In the CGS system of
units, the unit of mass is gram or g, and the unit of acceleration is cm/s². Therefore, the CGS unit of force is g
cm/s², which is called dyne or Dyn.
One Newton is the force needed to accelerate one kilogram of mass at the rate of tone metre per second
squared. 1 N=1 kgm / sq.sec.
The Newton (symbol: N) is the SI unit of force. It is names after Sir Isaac Newton The newton because of
his work on classical mechanics. A Newton is how much force is required to make a mass of one kilogram
accelerate at a rate of one metre per second squared
Different Laws for Composition and Resolution of Forces
A force is to be resolved into two components. Then: When one of the components is known, the second
component can be obtained by applying the triangle rule. When the line of action of each component is known,
the magnitude and the sense of the components are obtained by parallelogram law.

The process of substituting a force by its components so that the new effect on
the body remains the same is known as resolution of a force. The process of
finding out the resultant force of a number of given forces is called the composition/
compounding of forces.
Any force can be resolved into individual component forces in the same way as
individual component forces can be composed together. A force can be resolved
into two component forces graphically or with the use of trigonometry.

 The process of replacing a force system by its resultant is called composition.
 The Resultant of a pair of concurrent (occurring at the same time and gathering at the same point) forces can
be determined by means of Parallelogram Law, which states that:
Two forces on a body can be replaced by a single force called the resultant by drawing the diagonal of the
Parallelogram with sides equivalent to the two forces.
For example if F1 and F2 are two forces, the resultant ( R ) can be found by constructing the parallelogram.

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CITS : WCS - Mechanical - Exercise 4