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# Motion and Speed

Motion:

Motion is defined as the change in position of object with time. Earth, planets, stars, galaxies, atoms, molecules, blood in the body are all the examples of motion.  Motion may be in a straight line, or in circular path, or rotate or vibrate in nature.

Initial position of an object is described by a specific reference point which is called as origin. Motion of the object is described by the numerical value and not the direction of motion. The numerical value in physical quantity is its magnitude.

The shortest distance measured form the initial to the final position of an object is known as the displacement.

Magnitude of the displacement is not equal to the distance traveled by an object. Magnitude of the displacement for a course of motion may be zero but the corresponding distance covered is not zero.

In short, two different physical quantities – the distance and the displacement are used to describe the overall motion of an object and to locate its final position with reference to its initial position at a given time.

Consider the example of train which moves from station A to station B and comes back from station B to station A, here distance covered by train is from station A to B and then back B to A, but the displacement is zero as train is back to initial junction

When an object covers equal distance in equal time interval is called uniform motion, whereas when an object covers unequal distance in equal time interval is called non-uniform motion.

Speed:

The rate of motion of an object is to find out the distance traveled by the object in unit time is referred as speed.

SI unit of speed – meter/second or m/s

Speed of an object is described by its magnitude and is need not be constant.

For non-uniform motion, the rate of motion is described by their average speed.

Average speed – Total distance traveled

Total time taken

If an object travels a distance (s) in time (t) then its speed (v) is

V = s/t

Calculations:

Ex-1: An object travels 15m in 4s and then another 15m in 2s. What is the average speed of the object?

a) 5.00 m/s

b) 5.30 m/s

c) 5.33 m/s

d) 5.35 m/s

Average speed = total distance traveled / total time taken = 30 m/6 s   = 5 m/s

Total distance traveled by the object = 15m + 15m = 30m

Total time taken = 4s + 2s = 6s

Ex-2: Uniform motion is define as………………………..

a)      Equal distance in equal time interval

b)      Equal distance in unequal time interval

c)      Unequal distance in equal time interval

d)     Unequal distance in unequal time interval

Answer: When an object covers equal distance in equal time interval is called uniform motion.

Ex-3: Object covers unequal distance traveled by equal intervals of time is defined as……..

a)      Uniform motion

b)      Non-uniform motion

c)      Motion

d)     None of above

Answer: When an object covers unequal distance in equal time interval is called non-uniform motion.

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