# Motion and Time Class 7 Science Notes - Chapter 13

## An Introduction to Motion

### Distance

• Distance is the total path covered by the object in the given interval of time.
• Displacement is the shortest path covered by the moving object in the given interval of time.
• Distance=Speed×Time.
• Unit of distance is generally measured in units of length like metres, kilometres etc.

### Introduction to motion

• An object is said to be in motion if it changes its position with respect to time. Eg: A car moving on a road.
• An object is said to be at rest if the object does not change its position with time. Eg: A person standing on the ground.

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## Basics of Standard Units

### Units and their standardization

• The standard unit of distance is in metres.
• The standard unit of time is in seconds (s).
• The standard unit of speed is in metre per second (m/s).

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## Basics of Motion and Its Types

### Types of motion

Types of motion are generally divided into 3. They are:

1. Rectilinear / translatory motion: When a body is moving in a straight line, without changing its direction, then the body is said to possess translatory/rectilinear motion.
Eg: A car moving on a straight road.

2. Circular motion: When a body moves in the shape of a circle about a fixed point and a fixed radius, then the body is said to be in circular motion.
Eg: Motion of planets around the sun.

3. Period / Oscillatory motion: When the motion of a body repeats after fixed intervals of time, then the body is said to in the periodic/oscillatory motion.
Eg: To and fro motion of a simple pendulum.

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### Periodic or oscillatory motion

• Periodic or oscillatory motion is the motion in which a body repeats its motion after fixed intervals of time.
• Eg: To and fro motion of a  simple pendulum, Motion of a car in a  circular path, Motion of planets around the sun.

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### Oscillations of a simple pendulum

• When the bob of a simple pendulum moves from its mean position B to A and back to B again, then from B to C and back to B again, the pendulum is said to complete 1 oscillation.
• In the case of the simple pendulum, the time period is the total time taken by the pendulum to complete one oscillation.

## Time and Speed

### Speed (Average Speed)

• Speed is the total distance travelled by the object in a given interval of time.
• Speed = Distance travelled/time taken
• Unit of speed is generally measured in metre per second(m/s), kilometre per hour(km/h).

### Uniform and Non-Uniform Motion

1. Uniform motion: When an object moving along a straight line moves with a constant speed, then the object is said to be in uniform motion.
Eg: A car moving in a straight line with a constant speed.

2. Non-uniform motion: When an object moving along a straight line changes its speed with respect to time, then the object is said to be in uniform motion.
Eg: The motion of a train.

#### For More Information On Uniform and Non-Uniform Motion, Watch The Below Video:

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### Measurement of Time

• Unit of time is generally measured in seconds, minutes, hours.
• The time period is the total time taken by an object to complete one oscillation.

### Units of Time

Unit of time is generally measured in seconds, minutes, hours.

### Units of Speed

• Speed = Distance travelled in the total time interval.
• Unit of speed is generally measured in metre per second (m/s) and km/h( kilometre per hour).

### Speedometer and Odometer

• Speedometer records the speed of the vehicle directly in kilometre per hour (km/h).
• An odometer measures the distance moved by the vehicle directly in kilometres(km).

## Visualizing Motion

### Distance-time graph

• Distance-time graph is the graph plotted between the distance( in y-axis) and time ( in x-axis).
• The slope of a distance-time graph gives the speed of an object.

## Frequently asked Questions on CBSE Class 7 Science Notes Chapter 13: Motion and Time

### What is ‘Rectilinear’ motion?

It is a type of linear motion in which the direction of the velocity remains constant and the path is a straight line.

### What is ‘Average speed’?

Average speed is calculated by dividing the total distance that something has traveled by the total amount of time it took it to travel that distance.

### What are the uses of ‘Uniform motion’?

If an object is travelling with uniform motion, it is moving in a straight line at a constant speed.