# NCERT Class 7 Science Chapter 9 Motion and Time: Free PDF

NCERT Class 7 Science Chapter 9 introduces us to the concepts of motion and time. In this Physics lesson, we begin with definitions of motion and rest followed by the types of motion. Thereafter, we learn about the oscillations of a pendulum. After that, we will dive into definitions, formulae, and measurements of distance, time, and speed. In addition, we also explore measuring devices for distance and speed in a vehicle. To help you get started we have summarised all concepts in simplified form. Additionally, we also provide solutions to all questions following the chapter.

## Introduction to NCERT Class 7 Science Chapter 9: Motion and Time

To understand the concepts and formulas in the NCERT Class 7 Science Chapter 9, it is essential to learn about “motion” and “rest. Also, we will explore types of motion. Let us proceed!!

### Motion

An object is considered to be in motion when it alters its location over a period of time. For instance, a car travelling along a roadway.

### Rest

An object is considered to be stationary when it remains in the same position over a period of time, like a person standing on the ground.

### Types of Motion

There are three types of motion: Rectilinear motion; Circular motion; and Oscillatory motion.

• Rectilinear motion: When an object moves in a straight line without changing its direction, it is described as showing “rectilinear motion”. Another name for rectilinear motion is “translatory motion”. For example, a train moving on a railway track.
• Circular motion: When an object moves in a circular path around a fixed point with a constant radius, it is referred to as being in a state of “circular motion”. For instance, the movement of the moon around the Earth.
• Oscillatory motion: When an object’s motion repeats at consistent time intervals, it is described as periodic or oscillatory motion. For instance, the back-and-forth movement of a simple pendulum.

## Distance, Time, and Speed

Now, let us understand other definitions and concepts in NCERT Class 7 Science Chapter 9

### Distance

• “Distance’ refers to the entire route travelled by an object within a specific time frame.
• On the other hand, “displacement” signifies the shortest route taken by the moving object during the specified time period.
• Formula of Distance= Speed of an object * Time taken to travel the distance with a particular speed

### Speed

• Speed is a measure of the total distance covered by an object in a specific period of time.
• Formula of Speed= Distance travelled/ Total time taken to complete the distance

### Time Period

• The time period refers to the complete duration it takes for an object to finish one full oscillation or a particular distance.
• The formula of Time = Speed/Distance travelled at a specific speed

## Measuring Devices for Speed and Distance

NCERT Class 7 Science Chapter 9 also introduces us to devices used to measure speed and distance. Let us have a look at these.

### Odometer

An odometer directly measures the distance travelled by a vehicle in kilometres (km).

### Speedometer

The speedometer directly records the speed of the vehicle in kilometres per hour (km/h).

## Distance-Time Graph in NCERT Class 7 Science Chapter 9

A distance-time graph is a graphical representation with distance on the y-axis and time on the x-axis. The slope of a distance-time graph provides information about the speed of an object.

## NCERT Solutions Class 7 Science Chapter 9: Motion and Time

Let us now solve questions in NCERT Class 7 Science Chapter 9.

Ques 1. Classify the following as motion along a straight line, circular or oscillatory motion:

(i) Motion of your hands while running.

(ii) Motion of a horse pulling a cart on a straight road.

(iii) Motion of a child in a merry-go-round.

(iv) Motion of a child on a see-saw.

(v) Motion of the hammer of an electric bell.

(vi) Motion of a train on a straight bridge.

Ans:

(i) Oscillatory

(ii) Linear motion

(iii) Circular motion

(iv) Oscillatory motion

(v) Oscillatory motion

(vi) Linear motion

Ques 2. Which of the following is not correct?

(i) The basic unit of time is second.

(ii) Every object moves with a constant speed.

(iii) Distances between two cities are measured in kilometres.

(iv)The time period of a given pendulum is constant.

(v) The speed of a train is expressed in m/h.

Ans: The following are the incorrect statements

(ii) Every object moves with a constant speed.

(iv)The time period of a given pendulum is constant.

(v) The speed of a train is expressed in m/h.

Ques 3. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?

Ans:

Number of oscillations= 20

Total time taken to complete 20 oscillations=32 seconds

Therefore, Time period= Total time taken/Number of oscillations

= 32/20

= 1.6 seconds

Ques 4. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.

Ans:

Distance between two stations= 240 km

Total time taken to cover the distance between two stations by train= 4 hrs

Therefore, the speed of the train= Distance/Time

= 240 km/4 hrs

= 60 km/hr

Ques 5. The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.

Ans:

Reading of the odometer at 08:30 a.m. = 57321.0 km

Reading of the odometer at 08:50 a.m. = 57336.0 km

Therefore, the total distance covered by the car between 8: 30 a.m. and 8: 50 a.m.= Reading of the odometer at 08:50 a.m.- Reading of the odometer at 08:30 a.m.

= 57336.0 km-57321.0 km

= 15 km

Total time taken by the car = 8: 50 a.m. – 8:30 a.m.

= 20 mins

Therefore, Speed = Total Distance/Total Time Taken

= 15 km/20 min

= 0.75 km/min

Now, let us convert the speed into km/h

As, 20 min= (1/60)*20

= ⅓ h

Speed = Total Distance/Total Time Taken

= 15 km (⅓ h)

= 45 km/h

Ques 6. Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.

Ans:

Total time taken by Salma to travel from her house to school on a bicycle= 15 minutes

= 15 * 60

= 90 seconds

Speed of Salma’s bicycle= 2 m/s

Therefore, the distance travelled by Salma or the distance between her house and school= Speed*Time

= 2m/s*90s

= 1800 m

As, 1000 m=1 km

Therefore, 1800 m= (1/1000)*1800

= 1.8 km

Ques 8. Which of the following relations is correct?

(i) Speed = Distance*Time

(ii)Speed =Distance/Time

(iii) Speed =Time/Distance

(iv) Speed =1/(Distance*Time)

Ans: Option (ii) Speed =Distance/Time

Ques 9. The basic unit of speed is:

(i) km/min

(ii) m/min

(iii) km/h

(iv) m/s

Ans: Option (iv) m/s

Ques 10. A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:

(i) 100 km

(ii) 25 km

(iii) 15 km

(iv) 10 km

Ans: Option (ii) 25 km

Ques 12. The figure below shows the distance-time graph for the motion of two vehicles

A and B. Which one of them is moving faster?

Distance-time graph for the motion of two cars

Ans: Vehicle A is moving faster than vehicle B.

Ques 13. Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Ans: Option (iii)

## FAQs

Q1. What are the different types of motion?

Ans: The three different types of motion are Rectilinear motion, Circular motion, and Oscillatory motion.

Q2. What is an odometer?

Ans: An odometer directly measures the distance travelled by a vehicle in kilometres (km).

Q3. What is the formula of speed?

Ans: Speed= Distance/Time

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