GRADE : SUBJECT : PHYSICS 1 (POST MID TERM)

GRADE : VII SUBJECT : PHYSICS ASSIGNMENT : 1 (POST MID TERM)

G7_SCIENCE_ASSIGNMENT 1 HOME LEARNING RESOURCE of 13

Topic – Motion and Time (notes)

INTRODUCTION

In our daily life routine, we usually see some objects at rest and others in motion like birds

fly, fish swimming, planets moving around the sun, etc., are all in motion. When an object

changes its position with time, we often perceive an object to be in motion, e.g. when the

position of a car changes with time, we say that the car is moving or the car is in motion.

Types of Motion

The motion of all the objects are not of the same type. There are four different types of

motion shown by the different objects.

Rectilinear motion: The motion possessed by the body moving along a straight line path, is

called rectilinear motion,

e.g. the motion of a train on a straight bridge.

Circular motion: The motion possessed by a body when it moves along a circular path, is

called circular motion,

e.g. the motion of a child in a merry-go-round, motion of the earth around the sun in a

circular orbit.

Rotational motion: The motion possessed by a body when it spins about a fixed axis, is

called rotational motion,

e.g. the motion of the earth about its axis, spinning top, the motion of blades of a fan.



Periodic motion: The motion which repeats itself after regular intervals of time, is called

periodic motion,

e.g. the motion of the swing, to and fro motion of a simple pendulum

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.

• Unit of distance is generally measured in units of length like metres, kilometres etc.

Slow and Fast Motion

If one object covers a particular distance in less time and another object covers the same

distance in more time then the first object is said to be moving slowly while the second object

is said to be moving faster.

The Speed of an object

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

Types of Speed:

• Uniform Speed - When the object travels a fixed distance same time gaps, it is said to

have a uniform speed.

• Non-uniform speed - When an object covers different distances in different time gaps,

it is said to have a non-uniform speed.

• Average speed - The total distance travelled by an object divided by the total time

taken by the object is called its average speed



Speed = 𝐃𝐢𝐬𝐭𝐚𝐧𝐜𝐞

𝐓𝐢𝐦𝐞Average speed =

𝐓𝐨𝐭𝐚𝐥 𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞

𝐓𝐨𝐭𝐚𝐥 𝐭𝐢𝐦𝐞

Distance = speed × time Time = 𝐃𝐢𝐬𝐭𝐚𝐧𝐜𝐞

𝐒𝐩𝐞𝐞𝐝

Time

Time is familiar to everyone, yet it's hard to define and understand. Science, philosophy,

religion, and the arts have different definitions of time, but the system of measuring it is

relatively consistent.

Physicists define time as the progression of events from the past to the present into the

future.



Importance of time

Time is very important in the life of all living beings. In the morning when you are getting

ready for the school, your eyes are on the wall – clock or watch on your wrist, why? Because

you want to be ready before your school bus comes. Now think, what will you do, if your

wall – clock stops. You will ask your father or your neighbours about the time. Now think,

about the ancient days when no clock or watch was invented. How were our ancestors able

to guess about time?

Our ancestors used some natural event which repeated regularly to measure the time. For

example :

(i) They called the duration of time between one sunrise and the next sunrise as ‘a day’ .

(ii) Time duration between one full moon and the next full moon as ‘one month’.

(iii) One year was taken as the time duration taken by the earth to complete one

revolution of the sun. In the early days, knowledge of year, month and day was

sufficient to keep the life on track.

Simple devices :

To have some more approximation of time or length of a time period, people used some

simple devices such as sundial, sand clock or water clock etc.

Sundial :Sundial, the earliest type of timekeeping device, which indicates the time of day by

the position of the shadow of some object exposed to the sun’s rays. As the day progresses,

the sun moves across the sky, causing the shadow of the object to move and indicating the

passage of time.

https://www.britannica.com/science/day

https://www.britannica.com/place/Sun



Sand clock or hour glass :

Another device which was used by Romans, is a sand clock or

hour glass. It consists of two glass bowls fixed upside down with

a hole between them. (As shown in the figure), Sand filled in the

upper bowl passes into the lower bowl in a fixed time period.

Normally, it is one hour. When the sand glass is placed up side

down, the process repeats itself over the next hour. (Nowadays,

sundial and sand clock are used as showpieces in drawing

rooms).



Water clock

A water clock uses the rate at which water drips from one vessel

to another to measure time intervals. Water was allowed to drip

from one vessel to another vessel kept at a lower level. The time

taken by the entire water to drip from upper vessel to lower

vessel was used for measuring time intervals. Every time the

upper vessel is filled with water, its water takes exactly the same

time to drip into the lower vessel.

Clock and watches :

Today, a clock or a watch is used as a device to measure

time. The clocks could be made after the discovery of

pendulum by Galileo Galilei (1564 – 1642). It is an

interesting story. Once Galileo was sitting in a church. He

saw that a lamp suspended from the ceiling with a chain

was moving slowly from one side to other. He used his

pulse beat to find the duration of oscillation. He

experimented with various pendulums and found that a

pendulum of a given length always takes the same time to

complete one oscillation.

A simple pendulum

A simple pendulum consists of a small

metallic ball or a piece of stone suspended

to a rigid stand by a thread. The suspended

ball or stone piece is called a bob.

In rest position, the pendulum is at a

position ‘A’ which is called the mean

position.

When the bob of the pendulum is taken slightly to one side and released, it starts to move to

and fro. The to and fro motion of a pendulum is called periodic or oscillatory motion.



When the pendulum moves from its mean position A to position B and position B to position

C through position A and again to position A from position C, it is said that the pendulum

has completed one oscillation. The pendulum also completes one oscillation when it moves

from extreme position B to other extreme position C and comes back to position B.

Time period : The time taken to complete one oscillation by the pendulum is called its time

period.

Practically, the time duration for completing 10 or 20 oscillations is measured. The time

period is calculated by dividing the time taken by number of oscillations.

Time period = Time taken

Number of oscillations

Unit of time and speed

Standard unit Other unit

Time

Second (s)

Minute (min)

Hour (h)

Speed

Meter/second (m/s)

Meter/minute (m/min)

Kilometre/hour (km/h)

Conversion of km/h to m/s

Multiply by 5

18

Km /h m/s

Multiply by 18

5



Speedometer and odometer:

Generally the vehicles are equipped with the

apparatus used to measure the speed and distance

covered. The meter that shows the speed of the

vehicle in km/h is called speedometer and the

apparatus that shows the distance moved by a

vehicle, is called odometer. Mostly it is fitted in

the middle of speedometer. See in fig. Surely , you

have seen speedometer(with odometer) fitted on

the handle of a scooter, motor cycle and dash

board of cars, buses and trucks.

Graphs

o A graph is a picture or diagram that shows relation between two or more variable

quantities.

o A simple graph usually shows the connection between two numbers or

measurements in the form of a grid.

o A graph or a chart can be of different types based on number of quantities and

representation method.

Example of Different types of Graphs. Suppose we have the data for fruits liked by

percentage of students (out of 100) as below:



Distance – time graph

It is used to show the distance travelled and time taken to on a graph paper.

Here ,

Time taken is shown on x – axis

Distance is shown on y – axis

Distance – time graph for uniform speed

Suppose an object travels at uniform speed of 10 m/min

It means

Hours Distance travelled

0 0

1 10

2 20

3 30

4 40

Plotting it in graph

We show

Time on x axis

Distance on y axis



Distance – time graph for object moving at non uniform speed

Suppose an object travels as given in the table

Hour Distance travelled

0 0

1 20

2 70

3 150

4 200



Distance – time graph in case of stationary object

In case stationary object, distance travelled does not change

Suppose distance travelled in 1 second, 2 second, 3 second remains fixed at 40 km

In this case distance – time graph will be as follows

Distance – time graph summary



ASSIGNMENT – 1

Very short answer questions :

Q1. State one example of oscillatory motion.

Q2. Name two simple devices used in early days to measure the time.

Q3. What is a simple pendulum?

Q4. What is one oscillation?

Q5. What is speedometer?

Short answer type questions:

Q6. What do understand by speed and average speed?

Q7. A pendulum completes 20 oscillations in 25 seconds. Find its time period.

Q8. What is a uniform and non – uniform motion?

Q9. Distance between Delhi and Mathura is 140 km. A bus takes 3.5 hours to cover this

distance. Find average speed of the bus.

Q10. A car is moving at a speed of 54 km/h. Express this speed in m/s.

Long answer type questions:

Q11. Classify the following as rectilinear, circular or oscillatory motion.

i. Motion of a horse pulling a cart on a straight road

ii. Motion of a child in a merry-go-round

iii. Motion of a hammer on electric bell

Q12. The following is the distance – time table of a car moving on a road.

Time Distance from origin

9:50 am 0 km

10:00 am 4 km

10:10 am 10 km

10:30 am 20 km

10:45 am 25 km

11:00 am 40 km

(a) Use the table and draw distance – time graph.

(b) Is the motion of the car is uniform or non – uniform .

GRADE : SUBJECT : PHYSICS 1 (POST MID TERM)

Documents

Transcript of GRADE : SUBJECT : PHYSICS 1 (POST MID TERM)