# Units and Kinematics

By |

Physics is the study of nature and its law.The word physics drive from Greek word physis which means nature

Units

Measurement of any physical quantity involves comparison with a certain basic arbitrary chosen and widely accepted reference standard called unit

There are three types of measurement and they are

1.CGS  stands for centimetre–gram–second

2.SI or MKS stands for meter kilogram second or International System

3.FPS stands for Foot Pound Second

Greatest Unit

1 light year(unit of distance)=9.46×10^15 m

1 parsec=3.084×10^16m

1AU=1.5×10^11

1 nm=10 A’

SI Unit

The base of SI unit is seven which are Length,Mass,Time,Electric current,Thermodynamic temperature,Luminous Intensity and amount of substance.

Its supplementary unit is two which are Plane angle and solid angle

Physical Quantities:A physical quantity is a quantity in physics that can be measured, thus a physicalproperty that can be quantified. Examples of physical quantities are mass, amount of substance, length, time, temperature, electric current, light intensity, force, velocity, density, and many others.

Dimension of Physical Quantities:The dimension of the units of a derived physical quantity may be defined as the number of times the fundamental units of mass, length and time appear in the physical quantity. The expression for velocity obtained above is said to be its dimensional formula. Thus, the dimensional formula for velocity is [M0 L T 1].

Scalar Quantities:Physical quantities which have magnitude only and no direction. Ex.Mass,Volume,work,time,power etc.

Vector Quantities:Physical quantities which have both magnitude and direction and also obey triangular law. Ex.Displacement,force Etc.

Kinematics:

the branch of mechanics concerned with the motion of objects without reference to the forces which cause the motion is called kinematics

Distance:The length of actual path covered by a body in a particular time of period is said to be distance.it is always positive

Its unit is meter and it is scalar quantity

Displacement:Distance is a scalar quantity that refers to “how much ground an object has covered” during its motion that refers to “how far out of place an object is”; it is the object’s overall change in position.It may be positive,negative or zero.

Its unit is meter and it is scalar quantity.

Speed:Speed is the distance covered by a moving body in a part of time of interval.

Its unit is m/s and it is scalar quantity

Velocity:The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of its speed and direction of motion.It may be positive or negative.

Its unit is m/s and it is vector quantity

it is define in formula as velocity=Displacement/Time

Average velocity=2mn/(m+n)

If the body moving in a circular path after completing one cycle average velocity is zero.

Acceleration:Acceleration, in physics, is the rate of change of velocity of an object with respect to time. An object’s acceleration is the net result of any and all forces acting on the object.

Its unit is m/s² and it is a vector quantity.

It is define in formula as Acceleration=Velocity/Time