Motion and Time NCERT Solutions - Class 7 Science

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Chapter 13 – Motion and Time

NCERT Solutions for Class 7 Maths Chapter 13

Introduction

You have already studied about different types of motion in class VI. A motion as you know can be along a straight line, circular or periodic. In this chapter, you shall learn in detail about types of motion in detail.

13.1 Slow or Fast

You must have seen vehicles moving on the street. Just by observing those vehicles, you can easily identify which one is moving faster than the other. Read activity 13.1 carefully and observe the diagram to understand the concept of slow and fast movement of vehicles in a better way.

13.2 Speed

The distance covered by an object in a unit time is known as the speed of the object. You might have heard your father saying that the car is moving at a speed of 60 kilometers per hour. This statement simply means that the car is covering 60 kilometers in one hour. The formula of speed as used in this chapter is given below.

Speed = (Total distance covered)/(Total time taken).

In this section, you shall learn in detail the concept of speed and speed of different objects, in the context of the time taken by the objects to complete any particular task.

13.3 Measurement of Time

Have you ever wondered, if the clock wasn’t a part of our lives, how would we have known the time of the day? Well, our ancestors back then obviously did not have clocks with them. You know, many events in nature repeat themselves after specific intervals of time. In this section, you will also learn about a pendulum.

The to and fro motion of a simple pendulum is known as oscillatory motion or periodic motion. The small metallic ball of a pendulum is called the bob. The time taken by a pendulum to complete one oscillation is known as its time period. Observe figure 13.4 (a) and (b) to understand the working of the pendulum in a better manner.

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Units of Time and Speed

As all quantities are measured in metric units, there are units for the measurement of time and speed, as well. 

The S.I. unit of time = Second (s).

The S.I. Unit of Speed = Meters per second (m/s).

In this section, you shall learn about the different units of speed.

13.4 Measuring Speed

Now, you have learned about the calculation of distance and time. With the time taken by an object to cover a particular distance, you can easily calculate the speed of an object. In this section, you shall learn to calculate the speed of a ball. Similarly, you can use the formula as explained in this to calculate the speed of other objects as well. You must have noticed a meter-like device fitted in your vehicles. It has km/h written in the corner. It is the device that records speed in km/h and is known as a speedometer. The other meter that measures the distance moved by the vehicle is known as an odometer.

13.5 Distance - Time Graph

You have already studied about different graphs in mathematics. This section deals with the concept of a distance-time graph. The distance and time can be represented through a bar graph, a pie chart, as well as a line graph. In this section, you shall learn in detail about different distance-time graphs and their formation. Distance-time graphs are generally used to present the motion of any object in a pictorial form. The distance-time graph for the motion of an object that is moving with a constant speed is a straight-line graph. In this section, you will not only learn to read such graphs, but you will also learn the step method of plotting a graph.

Exercise Solutions: 13 Question (2 short questions and 11 long questions).

Extended Learning – Activities and Project (4 Questions).

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