Motion Class 9 | Physics Class 9 | Motion Physics

( I recommend all mobile users to read notes in landscape mode)*

MOTION

Motion


✓We specify the position of an object with respect to a fixed point as the reference point called the origin.
✓A body is said to be in motion if it changes its position continuously with respect to the origin with the passage of time.
✓A body said to be at rest if it does not changes its position continuously with respect to the origin with the passage of time.

Types of physical quantities

1. Scalar: It is described completely by its magnitude.
                  Ex:- Length, Time, Area
2. Vector: It is represented by number, unit, and direction.
                  Ex:- Force, Displacement

✓ There is a possibility of the addition and subtraction of vector.
 Example:  There are two forces F1 and F2.
                    F1 = 45 Newton Left
                    F2 = 25 Newton Right
                    Forces are opposite hence they will be subtracted and
                    the body will move in the direction of greater force.
                    Sum of Forces= 45 N Left - 25 N Right
                     Resultant Force= 20 N Left  

Distance and Displacement 

1. Distance: The length of the path covered by a body in any direction is
                      known as distance covered by the body.
2. Displacement: The distance covered by a body in a particular 
                                 direction is known as displacement.
✓ Displacement is the length between the initial and the final position.
✓ The displacement may be equal to zero if a body moves from point A on a circular path and end its journey at the same position.

Uniform and Non-Uniform Motion

1. Uniform Motion: A body continues its motion without changing its
                                    speed, this type of motion is uniform motion.
     Example: The motion of Army troops.
2. Non-Uniform Motion: A body is said to be in non-uniform motion
                                          if it covers unequal distance in equal interval
                                          of time.
    Example: Motion of a cricket ball.

Speed and Velocity

1. Speed: The length covered by a body in unit time without the 
                  condition of direction is known as speed.
 ✓Unit of Speed: Metre/Second (m/s)
✓Average Speed: The average speed of a body is the total distance
                                 traveled by the total time taken.
    Mathematical Equation,
     • Average speed=   S1+ S2 + S3 + S4 ............
                                     T1 + T2 + T3 + T4 ..........
2. Velocity: The rate of displacement of a body in a fixed direction is
                     known as velocity.
           Velocity= Displacement/Time

Acceleration and Retardation

✓ Acceleration is the rate of change of velocity of an object.
✓ Acceleration of moving objects is positive when the final velocity is maximum. Acceleration is negative when the final velocity is minimum.
✓ The negative acceleration is also known as retardation.
UNIT OF ACCELERATION: m/s²

Types of Acceleration

1. Uniform Acceleration: When a body travels on a straight line and 
                                               its velocity changes by the equal amounts
                                               at equal intervals of time.
2. Non-Uniform Acceleration: When a body changes its velocity 
                                                       anytime.
                                                 a= v-u/t.            ................(i) 
                         More equations related to Acceleration,
                                                 => at= v-u
                                  Therefore,  u+at=v         ...................(ii)
                                              and, u= v - at.        ..................(iii)
✓A geometrical relationship between two physical quantity is plotted on the x and the y axis is called a graphical plot or simply a graph. 

Three Equations of Motion

* Please watch the video to clear your concept and write derivation in notes also.
 


 1. v= u+at.  (Velocity time equation)
 2. S= ut+ 1/2 at².  (Position time equation)
 3. v²= u²+2as.  (Velocity position equation)

Uniform Circular Motion

✓ The motion of an object on a circular path is called circular m.otion.
✓ During circular motion, the direction of motion of any point is given by tangent to that point.
Examples of circular motion:
1. Earth and other planets move around the sun in a circular path.
2. A stone tied to a string and rotated in a circular motion, the tension produced in the string is due to centripetal force.
✓ The velocity of a body moving along a circular path at constant speed changes continuously the change in velocity give rise to acceleration in the body.

Angular Displacement

✓ The angle suspends at the center of a circle by the initial and final position of a body moving along the circumference of a circle is called angular displacement.
✓ Angular displacement is represented by θ (Theta).
       θ= Length of. Arc        
            The radius of the circle
✓ An angle subtended at the center of the circle where an arc is equal to radius then the angle is 1 radian.

Angular Velocity

✓ The rate of change of angular displacement is called angular velocity.
✓ It is denoted by ɷ (omega)

Angular Acceleration

✓ The rate of change in angular velocity is angular acceleration.
✓ It is denoted by alpha.
     Alpha=Omega/Time

If any doubt please ask in the comment section below.







 

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