7th Class Science Time and Motion Speed

       Speed

When a body moves, it covers some distance. How much distance does it cover in a given time or how long will it take to cover a particular distance? Such questions arise in our day to day life. To solve such queries a term "speed" is used. Speed is related to time and distance. With the help of speed we can find the distance or the required time to cover the particular distance. The standard unit of the time is second. The distance covered by an object in a unit time is called speed. Speed is a scalar quantity as it does not tell about the direction.

\[\text{Speed}\,\,\text{=}\,\,\frac{\text{Distance}}{\text{Time}}\]     

           Uniform Speed

If an object does not change its speed while moving, the object is said to be in uniform speed.

Look at the following figure

Speed of the car does not vary in different interval of time. Therefore speed of the car is uniform.

Graphical representation of uniform speed.

Time distance graph of a body, which has uniform, speed, is a straight line

          Non-uniform Speed

If an object changes its speed while moving, the object is said to be in non uniform, speed.

In the above figure, speed of the car varies at different interval of time. Therefore, speed of the car is non-uniform.

Graphical representation of non-uniform speed.

Distance-time graph of a body, which has non-uniform speed, is a curved line.

      Which one of the following is true for the uniform speed

(a) If speed of the object varies at different interval of time, the object has uniform speed

(b) If speed of the object is constant at different intervals of time, the object has uniform speed

(c) If a moving object suddenly comes to rest, the object has uniform speed

(d) All of these

(e) None of these

Answer: (b)

     A cyclist covers 25 km in first hour, 30 km in the second hour and 35 km in the third hour. The cyclist is in _____.

(a) Uniform motion

(b) Non uniform motion

(c) Cannot be find that the body is in uniform motion or in non uniform motion

(d) All of these

(e) None of these

Answer: (b)