MOTION

REST

A body is said to be in a state of rest when its position does not change with respect to a reference point.

MOTION

  • A body is said to be in a state of motion when its position change continuously with reference to a point.
  • Motion can be of different types depending upon the type of path by which the object is going through:
    (i) Circulatory motion/Circular motion – In a circular path.
    (ii) Linear motion – In a straight-line path.
    (iii) Oscillatory/Vibratory motion – To and fro path with respect to the origin.

SCALAR QUANTITY

It is the physical quantity having its own magnitude but no direction. Example: distance, speed.

VECTOR QUANTITY

It is the physical quantity that requires both magnitude and direction. Example: displacement, velocity.

DISTANCE AND DISPLACEMENT

  • The actual path or the length travelled by an object during its journey from its initial position to its final position is called the distance.
  • Distance is a scalar quantity that requires only magnitude but no direction to explain it. Example: Ramesh travelled 65 km. (Distance is measured by odometer in vehicles.)
  • Displacement is a vector quantity requiring both magnitude and direction for its explanation. Example: Ramesh travelled 65 km southwest from Clock Tower.
  • Displacement can be zero (when the initial point and final point of motion are the same) Example: circular motion.

DIFFERENCE BETWEEN DISTANCE AND DISPLACEMENT

UNIFORM AND NON-UNIFROM MOTIONS

Uniform Motion:

When a body travels an equal distance in an equal interval of time, then the motion is said to be a uniform motion.

Non-uniform Motion:

In this type of motion, the body will travel unequal distances in equal intervals of time.

Types of Non-uniform Motion

(i)Accelerated Motion:
When the motion of a body increases with time.
(i)De-accelerated Motion:
When the motion of a body decreases with time.

SPEED

  • The measurement of distance travelled by a body per unit time is called speed.
  • Speed (v) = Distance Travelled/Time Taken = s/t
  • SI unit = m/s (meter/second)
  • If a body is executing uniform motion, then there will be a constant speed or uniform motion.
  • If a body is travelling with non-uniform motion, then the speed will not remain uniform but have different values throughout the motion of such body.
  • For non-uniform motion, the average speed will describe one single value of speed throughout the motion of the body.
  • Average speed = Total distance travelled/Total time taken

Conversion Factor

Change from km/hr to m/s = 1000m/(60×60)s = 5/18 m/s

VELOCITY

  • It is the speed of a body in given direction.
  • Velocity = Displacement/Time
  • Velocity is a vector quantity. Its value changes when either its magnitude or direction changes.
  • For non-uniform motion in a given line, average velocity will be calculated in the same way as done in average speed.
  • Average velocity = Total displacement/Total time
  • For uniformly changing velocity, the average velocity can be calculated as follows : 
  • Avg. Velocity (vavg) = (Initial velocity + Final velocity)/2 = (u+v)/2
  • Where, u = initial velocity, v = final velocity
  • SI unit of velocity = ms-1
  • Velocity = Displacement/Time
  • It can be positive (+ve), negative (-ve) or zero.

ACCELERATION

  • Acceleration is seen in non-uniform motion and it can be defined as the rate of change of velocity with time.
  • Acceleration (a) = Change in velocity/Time = (v-u)/t
    where, v = final velocity, u = initial velocity
  • If v > u, then ‘a’ will be positive (+ve).

RETARDATION/DECELERATION

  • Deceleration is seen in non-uniform motion during a decrease in velocity with time. It has the same definition as acceleration.
  • Deaceleration (a’) = Change in velocity/Time = (v-u)/t
    Here, v < u, ‘a’ = negative (-ve).

EQUATION OF MOTION(FOR UNIFORMLY ACCELERATED MOTION)

  • First Equation: v = u + at
    Final velocity = Initial velocity + Acceleration × Time
  • Second Equation: s = ut + 1⁄2 at2
  • Third Equation: v2 = u2 + 2as

UNIFORM CIRCULAR MOTION

  • If a body is moving in a circular path with uniform
    speed, then it is said to be executing uniform circular
    motion.
  • In such a motion the speed may be the same throughout
    the motion but its velocity (which is tangential) is different at every point of its motion. Thus, uniform circular motion is an accelerated motion.

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