You Must Know
1. Measurement is the process of comparing some unknown quantity with some. known standard measure (unit) of that quantity.
2. The standard unit, of a given physical quantity, is a unit that is used, and accepted, all over the world.
3. The standard units, for three basic physical quantities; length, mass and time, are the metre (m), the kilogram (kg) and the second (s), respectively.
4. Motion implies a change in the position of an object, with respect to its surroundings, with time.
5. Motion, along a straight line, is known as ‘rectilinear motion.
6. Motion, along a curved path, is known as ‘curvilinear motion.
7. Circular motion is the motion of an object along the circumference of a circle.
8. In rotational motion, an object keeps on moving, ’round and round; about some definite axis, without changing its place.
9. In revolution, an object moves around a central point, changing its position continuously, and, usually, following a (nearly) circular path.
10. A motion, which regularly repeats itself after equal intervals of time, is called a ‘periodic motion.
11. In oscillatory motion, an object moves ‘to and fro’ along the same path.
12. A force may be thought of as a ‘push’ or a ‘pull’.
Something To Know
A. Fill in the blanks.
1. The standard unit of mass is the gram.
2. While sitting in a moving bus, we are in motion with respect to the surroundings.
3. A moving car, going on a narrow straight road, is having a (nearly) rectilinear motion.
4. The motion, of the needle of a sewing machine, is an example of an oscillatory motion.
5. The motion of the earth, around the sun, is periodic in nature.
B. Write True or False for the following statements.
1. Measurement is needed to make correct decisions. True
2. A metre scale can be used for measuring the length of a playground. True
3. The motion of the moon, around the earth, is a rectilinear motion. False
4. The motion, of the pedal of a bicycle, is a circular motion. True
5. The motion, of a giant wheel, is a rotatory motion. True
6. When we draw water from a well, we are pushing at the rope. False
C. Tick(✔) the correct option.
1. The standard unit of length is the-
metre
kilometre
millimetre
centimetre
Answer – metre
2. The standard unit of time is the-
second
day
year
minute
Answer – second
3. The motion, of the tip of a pen, while writing, is a/an-
rectilinear motion.
curvilinear motion.
oscillatory motion
rotatory motion
Answer – curvilinear motion.
4. Which of the following four ‘motions’ is different from the other three?
the moving blades of a fan
a spinning top
a fruit falling from a tree.
a potter’s wheel
Answer – a fruit falling from a tree.
5. The motion of a swinging pendulum is a/an
curvilinear motion.
oscillatory motion
rotatory motion
rectilinear motion
Answer – oscillatory motion
D. Answer the following questions in brief.
1. How does measurement help us in our day-to-day life?
Answer – Measurement is very important for our day-to-day life. Let us take example of a piece of cloth being bought for a dress. You need to know the exact length of cloth which needs to be bought. The cloth merchant uses a metre scale to measure the length of the cloth. If he would give a cloth piece on the basis of estimation, the cloth could be either less or more than what is required. If the cloth piece is less than what is needed, then it won’t be possible to make the dress. On the other hand, if the cloth piece is more than what is needed, it would result in wastage of cloth.
2. Which type of watch is used to measure time intervals in a ‘200 metre race’?
Answer – Stop watch is used to measure time intervals in a ‘200 metre race’.
3. When do we consider an object to be in motion?
Answer – When the position of an object changes with change in time, the object is considered to be in motion.
4. Name three different types of motions and give one example of each.
Answer – Three different types of motions are as follows:
(a) Rectilinear motion-car on straight road
(b) Curvilinear motion-car on a bend
(c) Rotatory, motion of wheel
5. State the difference between a ‘periodic’ and a ‘non-periodic’ motion.
Answer – Periodic motion -The motion repeats after certain time interval.
Example: motion of a pendulum
Non-periodic motion – The motion is not repeated.
Example: Motion of a train
E. Answer the following questions.
1. Why does a measurement need both a ‘number’ and a ‘unit’ for its complete specification?
Answer – We know that measurement is the process of comparing an unknown quantity with a known quantity where the known quantity is called the unit. While measuring some physical quantity with a unit we need to express the number of times that physical quantity is in terms of that unit. ‘Number of times’ and unit give the complete specification of a measurement. Let us take example of measure of your height. If someone says that your height is 140 then it does not specify whether it is 140 cm or 140 m or 140 inches. Similarly, if someone says that your height is in inches then it doesn’t specify the number of inches. On the other hand, if someone says that your height is 140 inches, then everything becomes clear.
2. Why is a foot step, or a hand span, not used as a standard unit of length?
Answer – Foot step or a hand span can be of different lengths in different people. If two people measure a particular length with their hand span, both of them would come with different numbers to express the measurement. It is clear that foot step or hand span can never be the same for all and hence cannot be used as standard unit for measuring the length.
3. Radha was performing an experiment in the Science Laboratory. The metre scale, that she was using to measure the length of a string, was worn out between its 1 cm and its 2 cm marks, due to overuse.
(a) She measures the length of a string by keeping its one end at the 3.0 cm mark. If the other end of the string ‘reads’ 92.8 cm, find the length of the string.
Answer – Length Final reading-Initial reading
92.8-389.8 cm
(b) Write the precautions, to be followed, when a metre scale is being used for measuring a given length.
Answer – The following precautions need to be followed when a metre scale is being used for measuring a given length:
The scale should be placed in such a way that its edge is along and parallel to the length which is being measured.
The zero mark of the scale should coincide with one end of the length to be measured.
The position of eye should be vertically above the point and in line with the reading to be taken. Change of the eye position would give wrong reading.
Worn-out or broken scale should not be used.
4. Explain the difference between ‘rest’ and ‘motion’. Give two examples of each.
Answer – When an object is in rest then its position does not change with change in time. On the other hand, when an object is in motion, then its position changes with change in time. A book on the bookshelf, a stone on pavement, etc. are examples of objects in rest. A moving car and a moving train are examples of objects in motion.
5. Distinguish between:
(a) Rectilinear and Curvilinear motion.
Give one example of each from our daily life.
Answer – When an object is moving on a straight path, it is said to be in rectilinear motion, for example, a fruit falling from a tree When an object is moving along a curved path, it is said to be in curvilinear motion, e.g. a car moving on a bend.
(b) Rotation and Revolution
Give one example of each from our daily life.
Answer – When an object moves around its axis, its motion is called rotation, e.g. a spinning top. top. When an object moves on a circular path, its motion is called revolution, e.g. movement of earth around the sun.
Give one example of each from our daily life.
6. Define the following types of motion:
(a) Rectilinear motion
Give one example for each of these two types of motion.
Answer – When an object is moving on a straight path, it is said to be in rectilinear motion, for example, a fruit falling from a tree and a bullet fired from a gun are in rectilinear motion.
(b) Circular motion.
Give one example for each of these two types of motion.
Answer – When an object is moving along a curved path, it is said to be in curvilinear or circular motion, e.g. a car moving on a bend and a horse running on a circular track are showing circular motion.
Value Based Question
When Karni’s mother saw her school calendar, she noticed that the annual sports day was still four months away. She, however, advised Karni to follow a regular, systematic practice schedule, right from the start. Karni followed her advice and did not deviate at all from her regular practice. On the sports day, she won the first prize in her event. Her mother told her that she succeeded in her efforts because she did her practice in a way similar to that of an object having a rectilinear motion.
1. Why did Karni’s mother compare her practice schedule with that of an object having a rectilinear motion?
Answer – In rectilinear motion, the object never deviates from its set path. Karni did not deviate from her chosen practice schedule. Hence, her mother compared her practice schedule with that of an object having a rectilinear motion.
2. State the values displayed by Karni.
Answer – Discipline, determination.
3. Play a game in which each participant picks up one (folded) paper chit, from a collection, having names of different types of motion written on them. The participant then has to speak of a ‘daily life situation’ that can be co-related with the type of motion written on her/his paper chit.
Answer – Do it yourself.
Something To Do
1. Create your own amusement park!
Visit an amusement park with your family, or teachers. Look closely at each ‘ride, and identify its types of motion.
Take a picture, or use a drawing, of each of the available ‘rides, and label their type of motion.
With the drawings/pictures of rides, set up your ‘amusement park, on a chart paper, or a cardboard. Also draw some roads, grass, sidewalks, and other things, you find at an amusement park.
After your amusement park has been set up, take your friends, or parents, on a ‘tour’ of it. Tell them about each ‘ride’ and the types of motion associated with that ride.
Answer – Do it yourself.
2. Take pictures of different objects, having different types of motion. Label the type/ types of motion in each case and make a collage titled “A Moment of Movement”. The pictures may be taken from old magazines/newspaper/books, etc.
Answer – Do it yourself.
3. Identify different types of motion from the ‘Word Puzzle’ given below. ‘Circular’ motion has been identified as an example for you.
Answer –