Concept of Motion
Rest :- If a body or object does not changes its position from
one point to other point with reference point, is said to be in Rest.
For Example :- Bus at bus stop.
Motion :- If a body or object changes its position from one
point to other point with reference point, is said in Motion.
For Example :- Train running from Delhi to Mumbai. In this
case the reference point of train is Delhi but train now running to Mumbai so
train is said in motion.
Types of Motion
1. Linear Motion :- If a body or object is moving in a
straight line path, the motion is said to be ‘Linear Motion”
For example :- A car is running on straight highway.
2. Circulatory Motion :- If a body or object is moving in a
circular path, the motion is said to be ‘Circulatory Motion”
For example :- The motion of earth around the Sun.
3. Oscillatory Motion :- If a body or object is moving in left
or right direction from its middle point, the motion is said to be ‘Oscillatory
Motion”
Note 1 :- In this year we only study about Linear Motion.
Physical Quantities :- Those quantities which are
represented by a number and measured directly or indirectly.
Types of Physical Quantities :-
1. Scalar Quantities :- In this quantities only magnitude is
needed to define the quantities, is said to be ‘Scalar Quantities’. There are
no need of direction to define these quantities.
For example :- Volume, Distance, Speed, Temperature, Density, Work, Energy etc
2. Vector Quantities :- In this quantities magnitude and
direction both are needed to define the quantities, is said to be ‘Vector
Quantities’. There is need of direction
to define these quantities.
For example :- Area, Displacement, Velocity, Acceleration, Force etc.
Distance :- The length of path of a motioning body or
object, said to be Distance.
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| science-class-9 |
In the figure 1 and 2, If a body moves A to B and B to C
Then Distance = AB + BC
Unit :- MKS metre (m), CGS centimeter (cm)
It is Scalar Quantity.
Distance may not be zero or negative.
Displacement :- The shortest distance travelled by an object, is said to be Displacement.
In the figure 1 and 2, If a body moves A to B and B to C
Then Displacement = AC
Unit :- MKS metre (m), CGS centimeter (cm)
It is Vector Quantity.
Displacement may be zero.
In the figure 1 and 2, If a body moves A to B and B to C and C to A.
In this object start motion from A and returns on A again so displacement is zero.
Speed :- The distance travelled by an object in per unit time is known as Speed.
Speed = Distance / Time
Unit :- MKS metre/second (m/sec), CGS centimeter/second (cm/sec)
It is Scalar Quantity.
Velocity :- The displacement by an object in per unit time is known as Velocity.
Velocity = Displacement / Time
Unit :- MKS metre/second (m/sec), CGS centimeter/second (cm/sec)
It is Vector Quantity.
Acceleration :- The rate of change of velocity with respect to time, is known as Acceleration.
Acceleration = Change in Velocity / Time
a = ( v - u ) / t
where u = initial velocity, v = final velocity
It may be positive or negative.
Unit :- MKS metre/second^2 (m/sec^2), CGS centimeter/second^2 (cm/sec^2)
It is Vector Quantity.
Uniform Motion :- If an object travels same distance in equal time intervals is known as Uniform Motion.
Non-uniform Motion :- If an object travels different distances in equal time intervals is known as non-uniform Motion.
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