Distance
Distance is the actual path travelled by a body in a given time. Consider a body travelling from A to B along any path between A and B. The actual length of the path that a body travels between A and B is known as the distance. Here if the body goes from A to B via C, the distance travel will be ACB. The distance travelled will be different for different paths between A and B.


Speed 
The distance travelled by a body in unit time is called its speed. 
Therefore, speed = Distance/Time

(a)    Uniform Motion : A body has a uniform motion if it travels equal distances in equal intervals of time, no matter how small these time intervals may be. For example, a truck running at a constant speed of say, 20 m/s, will cover equal distances of 20 metre, in every second, so its motion will be uniform.
                                        Or
If it moves along a straigth line with a constant speed it is said to be in uniform motion.

(b)     Non-Uniform Motion : A body has a non-uniform motion if it travels unequal distances in equal intervals of time. For example, If a car moving on a highway , we will find that it covers unequal distances in equal intervals of time. It covers :
5.9 metre in the 1st second,
15.7 metre in the 2nd second,
30 metre in the 3rd second, and so on.
                                 Or
If the speed of an object is not moving along a straigth line  keeps changing, its motion is said to be non-uniform.

Uniform and Non-uniform motion can be shown graphically also

 Ex. 3 A body satrts from A and moves according to given figure. Time for each interval is : 

tAB = 2s, tBC= 3s, tCB=2s, tBA = 3s, tAD= 4s


The distance, speed are as follows for different path.

Ex.4    A car travels a distance of 100 Km in 25 minutes to reach a place then calculate the speed of the car : 
(A) 4 km/min         (B) 4 m/min          (C) 400 m/min         (D) None of these

Ex.5     If an object  travels with the speed 18 km/hr for 20 minute find the distance covered by the object.
Sol.    Speed = 18 km/hr, time = 20 min
    Distance = speed × time

Types of Motion

  • Motion is defined as the change in position of an object.

  • Rectilinear Motion: When an object moves along a straight line, it is said to be undergoing rectilinear motion. 

For Example:

    1. A train moving along a railway track.
    2. A coin falling from a building, or a sprinter running a 100 metre race
  • Circular Motion: Have you seen the hands of a clock? The motion exhibited by the hands of a clock is called Circular Motion.
  • When an object is following a circular path of motion, it is called circular motion
  • In circular motion, the object remains at the same distance from a fixed point
  • Examples:
    • motion of stone tied in a thread and whirled.
    • motion of a blade of an electric fan.
    • The moon revolving around the earth.
    • motion of second’s hand in a clock.

  • Periodic Motion: When an object repeats its motion after a fixed interval of time it is said to be undergoing periodic motion. 

Motion in which an object repeats its motion after a fixed interval of time is called periodic motion.
Examples:

  • Oscillations of a pendulum
  • Motion f a swing.

 Rotational Motion:

  • Motion in which a whole body moves about an axis is called a rotational motion.
  • This motion can be easily understood by imagining Earth’s rotation. When the Earth spins on its own axis it is said to be undergoing rotational motion.

For Example:

  • Pendulum
  • motion of a top.

Combination of  two or more types of Motions: In some situations, the motion of an object may be a combination of two or more of the above mentioned types of motion.
Examples:

  • Motion of a ball on the ground. Here, the ball is rotating about an axis but the axis itself is moving along a straight line. Thus, the ball executes a rectilinear motion as well as rotational motion.
  • Motion of earth: Earth executes rotations on its axis and also revolves around the sun.

Conclusion:

  • Unit of measurements
  • It involves the comparison of an unknown quantity with some known quantity of the same kind.
  • This known fixed quantity is called a unit.
  • The result of measurement is expressed in two parts. One part is a number, the other part is the unit of measurement.
  • Circular motion: When a body moves in a circular path, its motion is known as circular motion.
  • Distance: Measurement of the gap between two points in certain units is called distance.
  • Measurement: Measurement means the comparison of an unknown quantity with some known quantity.
  • Motion: It is a state of objects in which they are moving that is, they are changing their place with time.
  • Periodic motion: Motion in which an object repeats its motion after a fixed interval of time is called periodic motion.
  • Rectilinear motion: When the objects change their position with time along a straight line, this type of motion is called rectilinear motion.
  • SI units: In October 1960 the 12th general conference on weight and measures adopted the International System of units to maintain uniformity all over the world. This system of units is called SI units.
  • Units of measurement: Measurement means the comparison of an unknown quantity with some known quantity. This known fixed quantity is called a unit of measurement.
  • Time: Time is the unit that measures how long it takes to do anything. Distance is measured concerning.
  • If an object is moving with some speed ‘s’ for a time interval ‘to, then the distance covered in that time will be = s x t