Motion and Time - Class 7 Science - New st. Mery English School

This chapter explains different types of motion such as uniform and non-uniform motion, measurement of time, and the use of simple devices like sundials, sand clocks, and water clocks. Students will also learn how to calculate speed, draw distance–time graphs, and observe motion in daily life with simple examples. Perfect for CBSE Class 7 students, teachers, and parents looking for clear and well-structured science notes.

Motion and Time - Class 7 Science - New st. Mery English School

 What is Motion?

Ans:- Motion is the change in position of an object with respect to its surroundings in a given interval of time.

Ex:- A moving car, A flying bird, A rolling ball, A moving train

How many types of motion?

Ans:- There are four types of motion.

1- Rectilinear Motion

2- Circular Motion

3- Periodic Motion

4- Rotational Motion

What is Rectilinear Motion?

Ans:- Motion along a straight line is known as Rectilinear Motion. It is also known as linear motion or Motion in a straight line.

Ex:- A car moving on a straight road, A train moving on a straight track, A laser beam travelling in a straight line, A ball rolling straight on the floor

Key points of Rectilinear Motion

1- In Rectilinear Motion, object does not change its direction.

2- In Rectilinear Motion, The path is straight.

3- In Rectilinear Motion, Speed may be uniform or non-uniform, but the path remains straight.

What is Circular Motion?

Ans:- The motion of an object in a circular path along the circumference of a circle is known as Circular Motion.   

Ex:- The movement of The hands of a clock, A stone tied to a string and swung in a circle, The Earth revolving around the Sun

Key points of Circular motion

1- In circular motion, The object keeps changing its direction, but stays on a circular path.

2- In circular motion, There is always a fixed centre around which the motion takes place.

What is Periodic Motion?

Ans:- A motion that repeats itself after equal intervals of time is known as Periodic Motion.

Ex:- Swinging pendulum of a clock, Heartbeat, Revolution of the Earth around the Sun, Day and night cycle

Key points of Periodic Motion

1- The Periodic motion happens in a pattern.

2- Each cycle of Periodic motion takes the same amount of time, known as the time period.

What is Rotational Motion?

Ans:- When an object spins or turns about a fixed axis, the motion is called rotational motion.

Ex:- The Earth rotating on its axis, Spinning top, Wheels of a bicycle or car

Key points of Rotational Motion

1- In Rotational Motion, The object does not move from one place to another, it spins in its own position.

2- In Rotational Motion, The line about which it rotates is called the axis of rotation.

Slow Motion and Fast Motion

An object that takes longer time to cover a certain distance is said to be exhibit slow motion but An object that takes less time to cover the same distance is said to be exhibit fast motion. 

When an object covers more distance in a short time, it is said to be in fast motion.

Ex:- A car moving at high speed.

        A cheetah running.

        A train moving quickly.

        A fan spinning at high speed.

When an object covers less distance in a long time, it is said to be in slow motion.

Ex:- A tortoise walking.

        A person walking slowly.

       The movement of a snail.

       The hands of a clock (hour hand).

How to Compare Fast and Slow Motion?

We compare  Fast and Slow Motion using speed. 

If two objects cover different distances in the same time

The one covering more distance → faster

The one covering less distance → slower

Ex:- A bicycle covers 10 km in 1 hour and A scooter covers 30 km in 1 hour. Here the scooter is faster than cycle because it covers more distance in the same time.

Speed

The distance travelled by an object in per unit of time is called Speed.

SI unit of distance is Metre. SI unit of time is Second.

So The SI unit of speed is Metre / Second (m / s ).

Formula of Speed:

$$\text{Speed} = \frac{\text{Distance}}{\text{Time}}$$

Example:

If a car travels 100 km in 2 hours. Find its speed.

Solution:- Distance = 100 km

                  Time = 2 hour

                 

$$\text{Speed} = \frac{100}{2} = 50 \text{ km/h}$$Uniform and Non-Uniform Motion

Uniform Motion

When an object covers equal distances in equal intervals of time, the motion is called uniform motion.

Example:- A car moving at constant speed, like 40 km/h.

                A train moving without stopping and without changing speed.

               If a car covers 10 km every 10 minutes, its motion is uniform.

Non-uniform Motion

When an object covers unequal distances in equal intervals of time, the motion is called non-uniform motion.

Example:- A car moving in traffic (sometimes slow, sometimes fast).

                 A child running in a playground, changing speed.

Distance - time graph

Distance - Time graph is a line graph which shows the relation between distance travelled and time taken to travel that distance by a moving body. In the distance - time graph , distance is plotted on the Y-axis and time is plotted on the X-axis.

Steps to draw Distance-time graph

Step - 1

Take a graph sheet and make two mutually perpendicular axis on it. Label the horizontal  as X-axis and the vertical as Y-axis.

Step - 2

Put marking on the X-axis and Y-axis as per the data given in the table with appropriate multiple units. The scale of the graph should be mentioned on the top right side of the graph.

Step - 3

Finally, the points are put on the graph corresponding to data given on the X-axis and Y-axis

Step - 4

All the encircled points are joined together, It results in the formation of distance-time graph.

Precautions while making Distance-Time Graph

Time

Time is the continued progress of events from the past, through the present, and into the future.

Time is the way we measure how long things take or when events happen.

Ancient methods of measuring time

The time interval between one sunrise and the next is a unit of time called day.

The time period from one sunset to sunrise is called night.

Time interval between one moon and the next is called a month.

Sundial

A sundial is a device that tells the time of the day by using the shadow made by the sun.

It has two main parts:

1. Dial Plate – A flat surface with hour markings.

2. Gnomon – A stick or triangular plate that casts a shadow.

When sunlight hits the gnomon, it creates a shadow on the dial plate. The position of this shadow tells the time.

How Does a Sundial Work?

• When the sun rises in the east, the shadow falls to the west.

• At noon (12 PM), the shadow is the shortest.

• In the evening, the shadow becomes long and falls toward the east.

The sundial uses this movement of the shadow to show the time.

Uses of a Sundial

• To tell time during the daytime

• To study the movement of the sun

• Used in ancient times before clocks were invented

Limitations of a Sundial

• It does not work at night

• It cannot work on cloudy or rainy days

• Time is not very accurate compared to clocks

1- The graph should be plotted using a sharp pencil and a ruler.

2- The scale of the graph should be taken appropriately according to the minimum and maximum observations.

Note:-

1- A straight line distance-time graph shows uniform motion.

2- When this graph is not a straight line, than it shows that body is executing non-uniform motion.