What is Uniform motion,Non-uniform motion,Speed,Velocity?

 

What is Uniform motion,Non-uniform motion,Speed,Velocity?

 

1.3. UNIFORM MOTION

 

When an object travels equal distances in equal intervals of time, howsoever small the interval may be, the motion of the object is said to be uniform.

 

For example, suppose a car covers 60 km in first hour, another 60 km in second hour, again 60 km in the third hour and so on. The motion of the car is uniform motion. Let us now understand the meaning of the words, ‘howsoever small the time interval may be used in the definition. In the above example, the car travels a distance of 60 km in each hour. In the stricter sense, the car should travel 30 km in each half hour ; 15 km in every 15 minutes ; 10 km in every 10 minutes, 5 km in every 5 minutes and 1 km in every one minute. Only then, the motion of the car can be said to be uniform. However, in broader sense, we do not mind even when time interval is big. The motion of the car is taken as uniform when it covers a distance of 60 km in every one hour.

 

1.4. NON-UNIFORM MOTION

 

When an object travels unequal distances in equal intervals of time, howsoever small the interval may be, the motion of the object is said to be non-uniform.

 

For example, suppose a car covers 40 km in first hour, 50 km in second hour, 30 km in third hour, 70 km in fourth hour and so on, the motion of the car is non-uniform, as it covers unequal distances in equal intervals of time.

 

In the stricter sense, when a car covers 60 km in every one hour, but not 1 km in every minute, its motion may be taken as non-uniform. Other examples of non-uniform motion are :

 

(i) A body falling freely under gravity has non-uniform motion as it covers unequal distances in each one second. The distance covered goes on increasing in every successive second, on account of acceleration due to gravity.

 

(ii) A train starting from one station and stopping at the other has non-uniform motion. This is because when the train starts and picks up speed, the distance travelled per second goes on increasing. And when the train approaches the next station of stoppage, the distance travelled per second goes on decreasing.

 

1.5. MEASURING THE RATE OF MOTION : CONCEPT OF SPEED

 

In covering a distance of 200 km from Ambala to Delhi, a driver takes about 4 hours. If another driver covers this distance in 3 hours, he is said to be driving faster. And if some driver covers the same distance in 5 hours, he is said to be slower.

 

The rate of motion of a body is usually measured by finding the distance travelled by the body in unit time. This quantity is referred to as the speed of the body. Thus,

 

Speed of a body is defined as the distance travelled by the body in unit time.

 

i.e.,                    Speed=Distance/Time                …(1)                      

If s is the distance travelled by a body in time t, its speed v, from eqn. (1) is

 

v=s/t                               …(2)

 

As SI unit of distance is metre (m) and that of time is second (s), therefore, SI unit of speed is metre/second. It is written as m/s or m s^-1.

 

When distance is measured in cm and time in second, the speed is in cm/s or cm s^-1. The speed of vehicles like car, bus truck, train etc. is expressed in kilometre/hour, written as km. p.h or km/h or

km h^-1?

 

Note that speed of a body is a scalar quantity. It has magnitude only. Speed of a body gives us no idea about the direction of motion of the body. The speed can be zero or positive. It can never be negative.

 

Uniform speed. When a body travels equal distances in equal intervals of time, howsoever small the intervals may be, the speed of the body is said to be uniform.

 

Non-uniform speed or Variable speed. When a body covers unequal distances in equal intervals of time, howsoever small the intervals may be, the speed of the body is said to be non-uniform or variable. In most of the cases, bodies move with variable speed or non-uniform speed. Therefore, we describe the rate of motion of such bodies in terms of their average speed.

 

The average speed of a body is obtained by dividing the total distance travelled by the total time taken,

 

i.e.,

 

average speed=total distance travelled/ total time taken

 

For example, in going from Ambala to lhi, total distance travelled = 200 km. If total time taken = 4 200 km hours, then average speed 50 km/h 4 h

 

The average speed of 50 km/h does not mean that the vehicle moved at this speed all the time. When the road is clear, the vehicle must have moved faster, and in city limits, the vehicle might have much lesser speed than the average speed.

 

1.6. SPEED WITH DIRECTION : CONCEPT OF VELOCITY

 

The rate of motion of a body gives us the speed of the body, wherein we have no information about the direction of motion of the body. The rate of motion of the body will be more comprehensive if we specify the direction of motion alongwith its speed. The quantity that specifies both the rate of motion and the direction of rate of motion is called velocity of the body.

 

Velocity of a body is the distance travelled by the body in unit time in a given direction.

 

In other words,

 

Velocity of a body is the speed of the body in a particular direction.

 

v=s/t

The unit of velocity is the same as that of speed, i.e., metre/second, represented as m/s or m s-! Other units of velocity are cm/s and km/h. Both, speed and velocity are represented by the same symbol (v). Velocity is a vector quantity whereas speed is a scalar quantity.

 

Uniform velocity (or constant velocity)

 

When a body is moving along a straight line, covering equal distances in equal intervals of time, howsoever small the interval may be, the velocity of the body is said to be uniform or constant.

 

For example, when a train travels over a straight horizontal track covering 60 km in every hour, the train is said to have uniform velocity of 60 km/h.

 

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