class 9th science notes
class 9th science notes, chapter 1 motion, laws of motion, class 9 science physics chapter 1 motion full detailed explain notes, revision notes, notes in easy language. all topic covered in detailed and explain more clearly. Distance and displacement, Uniform and non uniform motion, Acceleration, Equation of motion and much more.
class 9th science notes
Distance:- The actual length of the path covered by an object is called distance.
- The length of the actual path between the initial and final position of the body is called the distance.
- Distance has no sense of direction hence distance is a scalar quantity.
- It’s S.I unit is ‘m’ .
- Distance can never be negative.
Displacement:-
- The shortest distance between two points is called displacement.
- If the body moves in any direction then displacement is change in position.
- If the initial and final position of the body are same then the displacement will be Zero.
- Hence, from above result we can say that displacement will be positive, Negative or zero.
- Displacement has sense of direction therefore displacement is a vector quantity.
- S.I unit of displacement is ‘m’ .
- It is not depend on path but distance is depend on path.
- Distance is equal to displacement when it goes to straight line.
- If we move on the straight lines in positive direction then distance is equal to the displacement but we move in curved path then distance is greater than displacement.
Uniform and non uniform motion
Uniform motion:- When a body moves in such a way that it covers equal distance in equal interval of time however small the time interval may be then speed is said to be uniform motion.
Non uniform motion:- if body travels equal distance in unequal interval of time/ unequal distance cover in equal interval of time then it is called non uniform motion.
Speed:-
- The distance traveled by a body per unit time over a short interval of time is called its speed.
- S.I unit of speed is m/s.
- C.Gs unit of speed is cm/s.
- speed is the scalar quantity.
Velocity:-
- The displacement covered by a body per unit time is called velocity.
- S.I unit of velocity is m/s.
- C.Gs unit is cm/s.
- velocity is vector quantity it has both magnitude and direction.
Average speed:-
- It is the ratio of total distance traveled by total time taken.
- It is a scalar quantity.
- It’s S.I unit is m/s.
- It is denoted by ‘V’ .
Acceleration:-
Rate of change of velocity with respect to time.
Acceleration = final velocity – initial velocity/ time
a = v – u / t
- S.I unit of acceleration is m/s2.
- Acceleration may be positive, Negative or Zero.
Acceleration are two types
- Uniform Acceleration:-
When a body travels in a straight lines and its velocity changes by equal amounts is equal interval of time then it is called Uniform acceleration.
2. Non uniform Acceleration:-
When the velocity of a body changes by unequal amount in equal interval of time then it is called non uniform acceleration.
- Positive acceleration is simply called acceleration.
- Negative acceleration is simply called Retardation.
First equation of motion
V = u + at
Proof :- we know that
acceleration = change in velocity/ time taken
a = v – u/t
at = v – u
at + u = v
or
v = u + at
Where,
V = final velocity
U = initial velocity
T = time
A = acceleration
Second equation of motion
S = ut + 1/2 at2
Proof
Average speed = u + v/2
Distance = Average speed * time
S =( u + v/2 )* t
We know that
v = u + at
put value of v
S = ut + ut + at2/ 2
= 2 ut + at˄2/ 2
S = ut + 1/2 at2
Third equation of motion
v2 = u2 + 2as
We know that,
V = u + at
and ,
S = ut + 1/2 at2
From V = u + at
t = v – u/a
S = ut + 1/2 at2
S = u*( v -u/a) + 1/2 * a *( v -u/a )2
2as + u2 = v2
v2 = u2 + 2as