Measurement Of Length And Motion

Hello my dear students! Welcome to today's science lesson. I am so happy to see all of you ready to learn something new and interesting. Today, we are going to study Chapter 5 from your science textbook - Measurement of Length and Motion. This is a very important chapter because measurement is something we use in our daily life, every single day. Whether you are measuring your height, or checking how far your school is from your home, or even when your mother measures flour for making roti - everywhere we need to measure length. So let's begin our journey into the world of measurement and motion!

Let me start with a story. There is a girl named Deepa, who is eleven years old and she lives in a town in Haryana. One day, Deepa needed a new uniform because she had grown taller. Her mother took her to a cloth shop. Can you guess what happened next? Her mother asked the shopkeeper for a two-metre cloth piece. The shopkeeper measured the cloth using a metal measuring rod. Then, the tailor took her measurements using a flexible measuring tape. Now here is something interesting - her mother instructed the tailor to increase the length of her uniform by char angula. Do you know what char angula means? It means four fingers width. This is a traditional way of measuring that our grandparents and great-grandparents used. So students, let me ask you - are the tape and rod similar to the scale that you have in your geometry box? And what did Deepa's mother mean by char angula? Char angula is a unit of measurement used traditionally, where the width of four fingers is used to measure length. Isn't that interesting?

Now, Deepa shared this experience with her school friends - Anish, Hardeep, Padma, and Tasneem. And this led to a wonderful discussion amongst them about measurement. Let me tell you what they discussed.

Hardeep said, "I have seen my grandmother measuring cloth by the length of her arm." Have you ever seen your grandparents or elders measuring cloth like this? It's quite common in India. Then Padma said, "I have seen how a farmer measures length to divide his field into beds. He walks and counts the number of his strides." Anish added, "Oh, not just the length of the strides - sometimes they also use the length of their feet to measure." You see, students, people have been using different parts of their body to measure length since ancient times. This is called using non-standard units.

Now Deepa got excited and said, "Measuring length using body parts must be so much fun! Let us also measure something using a body part." They decided to measure the length of the table in their classroom. But which body part should they use? Deepa suggested, "Let us use our handspan. I have seen my mother using it. She calls it balisht." So they all started measuring the table using their handspans. Let me tell you what they found.

Anish found slightly more than 13 handspans. Padma found exactly 13 handspans. Tasneem found slightly less than 13 handspans. Deepa found between 13 and 14 handspans. And Hardeep found 14 handspans. Now here is the interesting part - all of them measured the same table, but they got different numbers! Padma said, "Oh, the number of handspans is different for all of us. So, what can we say about the length of the table?" Hardeep asked thoughtfully, "But why should the number be different?" Tasneem guessed, "Our handspans are of different sizes." And they all checked this by putting their handspans along each other and confirmed that indeed, their handspans were of different sizes.

So students, what did Deepa and her friends learn from this? They learned that handspans and other similar units, such as length of hand, foot, fist or fingers, differ from person to person. This is a very important observation. If I measure a table with my handspan and you measure the same table with your handspan, we might get different answers. This would create confusion, wouldn't it? So there is a need for such a unit for which measurements of the same length made by different people do not differ. This is why we need standard units.

Now, let me tell you something fascinating about India's history of measurement systems. India has a rich history of measurement systems dating back to ancient times. Angula, which means finger width, multiples of angula, dhanusa, and yojana are some of the units mentioned in ancient Indian literature. These were used in measuring artefacts, architecture, and town planning. The angula is still used by traditional craftspeople like carpenters and tailors. Several objects with ruled markings, which could be scales, have been excavated from sites of the Harappan Civilisation. Isn't that wonderful? Our ancestors were so advanced in measurement systems!

Now let's move on to the next important topic - Standard Units. Students, several systems of units evolved with time in different parts of the world. However, when people started travelling from one place to another, it created a lot of confusion. Can you imagine if someone from India went to America and tried to buy cloth using angula or handspan? It would be very confusing for everyone! This led to different countries coming together and adopting a set of standard units of measurement. The system of units now used is known as the 'International System of Units' or SI units. This system is used all over the world, which makes communication and trade much easier.

Now, what is the SI unit of length? The SI unit of length is metre. Its symbol is m. A metre scale is shown in your textbook. One metre is divided into 100 equal divisions. Each division is called a centimetre. You may be familiar with a smaller part of the metre scale, typically 15 cm long, which is commonly used in geometry boxes.

Let me tell you how to read a 15-cm scale. It has markings in centimetres from 0 to 15. The length of any section between two consecutive big marks, such as between 1 and 2 or between 5 and 6, is 1 centimetre. Now observe carefully - these sections of 1 cm length are further divided into 10 equal parts. The length of one of these smaller parts is called a millimetre. 1 mm is the smallest value of length that you can measure using this scale. Remember, 1 mm is equal to one-tenth of a centimetre, which we write as 1 mm = 0.1 cm.

For measuring larger lengths, we use a larger unit called a kilometre, which is equal to 1000 metres. And for measuring smaller lengths, we use units such as centimetre or millimetre. Let me write these relationships for you to remember:

1 kilometre equals 1000 metres 1 metre equals 100 centimetres 1 centimetre equals 10 millimetres

Now students, let me ask you a question. Would it be convenient to use the unit metre to measure larger lengths, such as the length of a railway track between two cities? Of course not! It would be ridiculous to say the railway track is 500,000 metres long. We would say 500 kilometres instead. Similarly, would it be convenient to use metre to measure smaller lengths, such as the thickness of a page of a book? No, because a page is very thin - it would be something like 0.01 centimetre or 0.1 millimetre. So we choose the appropriate unit based on what we are measuring.

In some scales, you might have noticed another scale marking. This scale marking is in inches, where 1 inch equals 2.54 centimetres. In earlier days, units such as inch and foot were used to measure length. These units are still used by some people, especially in countries like Britain and America.

Now, let me ask you a very important question. Suppose we all measure the length of the table again, but this time using a metre scale. Will our results still be different? The answer is no, but we should first learn the correct way of using a scale to measure length. So let's learn about the correct way of measuring length.

For measuring any length, we need an appropriate scale. For example, if you want to measure the length of your pencil, you may use a 15-cm scale. Similarly, if the height of a room is to be measured, you may need a metre scale or a measuring tape. You cannot directly measure the girth of a tree or the size of your chest using a metre scale. For such measurements, a flexible measuring tape, such as a tailor's tape, is more suitable.

While measuring lengths, we need to take care of some important points. First, let me tell you about the correct way of placing the scale. Place the scale in contact with the object along its length. Make sure the scale is touching the object properly. If you place the scale away from the object, your measurement will be wrong.

Second, what is the correct position of the eye while reading the scale? This is very important! For example, if you are trying to measure the length of a pencil by aligning it with a scale, the position of your eye should be directly above the tip of the pencil. If your eye is at an angle, you might read the wrong measurement due to parallax error. This is called the correct position of the eye.

Now, what should we do if the ends of the scale are broken or the zero marking is not clear? Can we still use such a scale? Yes, we can! With such a scale, use any other full mark of the scale, say 1.0 cm. Then you must subtract the reading of this mark from the reading at the other end. For example, if the reading at one end is 1.0 cm and at the other end it is 10.4 cm, therefore the length of the object is 10.4 cm minus 1.0 cm, which equals 9.4 cm. This is a very useful technique to know!

Now students, let me tell you about how visually challenged students measure lengths. They use scales with raised markings that can be felt by touching them. This is a wonderful example of how accessibility features are designed for everyone.

Now let's do Activity 5.1 together. Select some objects around you, such as a comb, a pen, a pencil, and an eraser to measure their lengths. Measure their lengths one by one using a metre scale and note down the measurements. While writing the length, do not forget to write the unit also. Thus, your result will consist of two parts - one part is a number and the other part is the unit of measurement. For example, if your pencil is 14 centimetres long, 14 is the number and centimetre is the unit.

Now, some of your friends in the class would have measured the length of the same objects. Compare the lengths measured by you with that of your friends. Are the measured lengths the same or slightly different? If they are not the same, discuss the possible reasons for the differences. There could be small differences due to how accurately you placed the scale or how accurately you read the measurement.

Now, why are some length measuring devices made up of flexible materials? This is because some objects have curved surfaces, like the circumference of your arm or the girth of a tree. A flexible tape can easily bend and measure such curved lengths accurately. A rigid scale cannot measure curved surfaces properly.

Now, an important point about writing units. Units of length, such as kilometre, metre, centimetre and millimetre, begin with a lowercase letter, except at the beginning of a sentence. Their symbols km, m, cm and mm are also written in lowercase letters, and are never followed by 's' for the plural. Note that a full stop is not written after the symbol, except at the end of a sentence. While writing the length, always leave a space between the number and the unit. For example, we write 5 cm, not 5cm or 5 cms.

Now let's learn about measuring the length of a curved line. This is a very useful skill. Anish and his parents fixed electric string lights on the arches of the verandah of their house for a celebration. How would they have measured the required length of string lights? The arches are curved, not straight. So how do we measure the length of a curved line?

In the case of a curved line, measurements can be made with the help of a flexible measuring tape or by using a thread. Here is how we do it - take a thread and place it along the curved line carefully. Then straighten the thread and measure its length using a metre scale. This gives us the length of the curved line. Simple, isn't it?

Now let's move on to another important topic - Describing Position. One day, the teacher informed her students that she had planned an educational visit to a nearby garden. She asked the students to reach there directly in the morning. Deepa and her friends started discussing whether the garden would be closer than their school or farther. Tasneem and Padma said that the garden would be closer, while Deepa and Anish felt that the school would be closer. Hardeep thought that both would be almost at an equal distance.

Who do you think is correct? Actually, all of them could be correct! Then why are their observations different? They are locating the distances of the school and garden from their houses. Each of them lives at a different location, so the distance from their house to the school and from their house to the garden would be different. If, instead, each of them had thought of distances from the same object or point, say the bus stand, then their observations would have been the same.

This brings us to an important concept - when distance is stated with respect to a fixed object or point, then this point is called a reference point. The reference point is very important in measuring distance and describing position.

Let me give you another example. A few days later, Hardeep told his friends, "Let us all go to the playground. The sports teacher wants us to help her to draw lines with chuna powder for making the Kabaddi court for the sports day." They needed a longer measuring tape. They first decided the point on the ground from which they would measure the distances to start drawing the lines. This point is their reference point.

After a few days, Padma was travelling by bus to visit her grandparents in Delhi. She was eager to reach Delhi and was reading the kilometre stones on the side of the road. On one of the kilometre stones, it was written 'Delhi 70 km'. Further on, the next kilometre stone read 'Delhi 60 km'. Each kilometre stone indicated that she was getting closer to her grandparents' house. These kilometre stones indicated her distance from Delhi. So, Delhi is the reference point in this situation.

What do such kilometre stones indicate? They indicate the distance from Delhi. When the kilometre stone reads 'Delhi 70 km', we can say that the position of Padma is 70 km from Delhi. When the kilometre stone reads 'Delhi 60 km', the position of Padma is 60 km from Delhi. So Padma could conclude that she was getting closer to her destination because the distance was decreasing.

Now, does this mean that the position of Padma, with respect to the reference point, is changing with time? Yes, it is! When does the position of an object change with respect to a reference point? It changes when an object is moving. This leads us to the next important topic - Motion.

Let's do Activity 5.2 together. Look around and prepare a list of five objects that are in motion and five objects that are at rest. Think about how you decided whether an object was in motion or at rest. Write your explanation, which we call justification, in your notebook.

An object is said to be in motion if its position changes with respect to the reference point with time. If an object is not changing its position with respect to the reference point with time, it is said to be at rest.

Now, here is something very interesting. Deepa looked around her in the bus and noticed that all the passengers were seated. She looked around again after a minute and found them still occupying their seats. She wondered, 'Are they moving?' She concluded that the position of the passengers was not changing with time. Therefore, they were certainly at rest. However, when she looked outside, she felt they were in motion as their positions were changing with respect to things outside.

The reference point is important in deciding whether an object is at rest or in motion. If Deepa considered herself, or the bus, as the reference point, then the passengers were at rest. However, if she considered any object outside the bus, say a building, as the reference point, then the passengers and the bus were in motion.

This is a very important concept, students. Whether something is at rest or in motion depends on the reference point you choose. There is no absolute rest or absolute motion. Everything depends on what you are comparing with.

Now, let me ask you a thought-provoking question. Suppose you are travelling on a ship which is moving at a constant speed along a straight line on a calm sea. Suppose there is no window on the ship. Is there any way that you can determine whether the ship is moving or is stationary? Think about this. If there are no windows and the sea is calm, and the ship is moving at constant speed without any bumps, you might not be able to tell if you are moving or stationary. This is because all the objects inside the ship are moving with you, so relative to each other, nothing seems to be changing. This is why reference points are so important!

Now let's learn about the different types of motion. Let's do Activity 5.3. Take an eraser and drop it from a certain height. Observe its motion. Does it move along a straight line? Yes, it does! When an orange drops from the tree, does it move in a straight line? Yes! Have you seen the Republic Day parade? Recall the march-past of students during the parade. Do they move on a straight-line path? Yes, they do! When a heavy box is pushed, it may also move along a straight line.

When an object moves along a straight line, its motion is called linear motion. Can you identify linear motion in your surroundings? A car moving on a straight road, a ball falling straight down, a student walking in a straight line - all these are examples of linear motion.

But do things always move along a straight line? You might have enjoyed playing on swings and merry-go-rounds. Are these types of motion also linear motion? No, they are not!

Let's do Activity 5.4. Tie an eraser or a potato to one end of a thread. Hold the other end of the thread with your hand and whirl it. Observe its motion. Is the motion of the eraser the same as that of a merry-go-round? Yes, it is! When an object moves along a circular path, its motion is called circular motion. The earth moving around the sun, a wheel of a bicycle, a merry-go-round - all these are examples of circular motion.

Now let's do Activity 5.5. Tie an eraser or a potato to one end of a thread. Hang the eraser by holding the other end of the thread. Keep your hand steady. Using the other hand, take the eraser slightly to one side and then release. Does it start moving to and fro? Yes! Is its motion similar to the motion of a swing? Yes! When an object moves to and fro about some fixed position, its motion is called oscillatory motion. The motion of a swing, the motion of a pendulum in a clock, the motion of a guitar string when plucked - all these are examples of oscillatory motion.

Let's do Activity 5.6. Take a thin metal strip of about 50 cm long. Hold its one end pressed to a table. You may use a few books or a brick to hold it. Press the free end of the strip slightly and let it go. Observe the motion of this end of the strip. Does it move up and down? Yes! This is also an example of oscillatory motion.

Now, here is something interesting to know. If an object repeats its path after a fixed interval of time, its motion is said to be periodic. When an object is in circular motion, it moves along the circular path again and again. An object in oscillatory motion also repeats its motion while moving to and fro. Both circular and oscillatory motion are periodic in nature.

Now let's do Activity 5.7. Look at the picture of a children's park in your textbook or visit a children's park. Observe different kinds of motions. Classify them as linear, circular or oscillatory motion. List them in the table given in your textbook. Give your justification for why you put each in a certain category. For example, a swing shows oscillatory motion because it moves to and fro. A merry-go-round shows circular motion. A slide shows linear motion as children slide down in a straight line.

Now students, let me summarize what we have learned so far. We learned about measurement, standard units, the SI system, different units of length, how to measure correctly, measuring curved lines, reference points, motion, and types of motion. Now let's practice some exercises to check our understanding.

Let's look at the questions in "Let us enhance our learning".

Question 1: Some lengths are given in Column I of Table 5.5. Some units are given in Column II. Match the lengths with the units suitable for measuring those lengths.

Column I has: Distance between Delhi and Lucknow, Thickness of a coin, Length of an eraser, Length of school ground.

Column II has: centimetre, kilometre, metre, millimetre.

Let me think about each one. Distance between Delhi and Lucknow is very large - it is hundreds of kilometres. So we should use kilometre. Thickness of a coin is very small - just a few millimetres. So we should use millimetre. Length of an eraser is small - about 5 to 8 centimetres. So we should use centimetre. Length of school ground is quite large - maybe 100 to 200 metres. So we should use metre.

So the matches are: Distance between Delhi and Lucknow - kilometre Thickness of a coin - millimetre Length of an eraser - centimetre Length of school ground - metre

Question 2: Read the following statements and mark True or False against each.

(i) The motion of a car moving on a straight road is an example of linear motion. This is TRUE because the car is moving along a straight line.

(ii) Any object which is changing its position with respect to a reference point with time is said to be in motion. This is TRUE - this is exactly the definition of motion.

(iii) 1 km = 100 cm. This is FALSE because 1 km = 1000 m, and 1 m = 100 cm, so 1 km = 100,000 cm, not 100 cm.

Question 3: Which of the following is not a standard unit of measuring length?

(i) millimetre - this IS a standard unit (ii) centimetre - this IS a standard unit (iii) kilometre - this IS a standard unit (iv) handspan - this is NOT a standard unit because it varies from person to person

So the answer is handspan.

Question 4: Search for the different scales or measuring tapes at your home and school. Find out the smallest value that can be measured using each of these scales. Record your observations in a tabular form. This is an activity for you to do at home. Look at different scales - your geometry box scale probably measures up to 15 cm with smallest division of 1 mm. A metre scale measures up to 1 metre with smallest division of 1 cm or 1 mm. A measuring tape can measure longer lengths. Find these and note down the smallest measurement value for each.

Question 5: Suppose the distance between your school and home is 1.5 km. Express it in metres. We know 1 km = 1000 m, so 1.5 km = 1.5 × 1000 = 1500 m. So the answer is 1500 metres.

Question 6: Take a tumbler or a bottle. Measure the length of the curved part of the base of glass or bottle and record it. This is another activity. You need to use a thread to measure the curved length, then straighten the thread and measure with a scale.

Question 7: Measure the height of your friend and express it in (i) metres (ii) centimetres and (iii) millimetres. This is an activity for you to do. If your friend is 150 cm tall, then in metres it is 1.5 m, in centimetres it is 150 cm, and in millimetres it is 1500 mm.

Question 8: You are given a coin. Estimate how many coins are required to be placed one after the other lengthwise, without leaving any gap between them, to cover the whole length of the chosen side of a notebook. Verify your estimate by measuring the same side of the notebook and the size of the coin using a 15-cm scale. This is an interesting activity. First estimate, then measure and verify.

Question 9: Give two examples each for linear, circular and oscillatory motion.

Linear motion examples: A car moving on a straight road, a falling stone, a person walking in a straight line.

Circular motion examples: The earth revolving around the sun, a wheel of a bicycle, a merry-go-round.

Oscillatory motion examples: A swing, a pendulum of a clock, a guitar string when plucked.

Question 10: Observe different objects around you. It is easier to express the lengths of some objects in mm, some in cm and some in m. Make a list of three objects in each category and enter them in the table.

For millimetre: thickness of a coin, diameter of a wire, thickness of a paper For centimetre: length of a pencil, width of a book, height of a glass For metre: height of a door, length of a room, height of a person

Question 11: A rollercoaster track is made in the shape shown in Fig. 5.19. A ball starts from point A and escapes through point F. Identify the types of motion of the ball on the rollercoaster and corresponding portions of the track.

This question refers to a figure in your textbook. Generally, in a rollercoaster, the ball might have linear motion on straight portions, circular motion on curved portions, and oscillatory motion on wavy portions. You need to look at the figure and identify each portion.

Question 12: Tasneem wants to make a metre scale by herself. She considers the following materials for it - plywood, paper, cloth, stretchable rubber and steel. Which of these should she not use and why?

She should not use stretchable rubber because rubber stretches when pulled, so measurements made with it would not be accurate. The other materials - plywood, paper, cloth, and steel - can be used, though some are more durable than others.

Question 13: Think, design and develop a card game on conversion of units of length to play with your friends. This is a fun activity. You can make cards with different lengths and units, and players have to match equivalent lengths.

Now let's look at the "Learning further" section.

First, can you find the thickness of a single page of your notebook or textbook using a scale? Think of a way and write it. Carry out the activity and report your result. This is tricky because a single page is very thin. One way is to measure the thickness of many pages together, say 100 pages, and then divide by 100 to get the thickness of one page.

Second, collect fallen leaves from the same tree. Identify the name of the tree whose leaves you have taken. Measure length and breadth of all these leaves using a 15-cm scale. Record your observations. Then discuss why the leaves of the same tree vary in length and breadth. This could be due to different ages of leaves, position on the tree, sunlight exposure, and other environmental factors.

Third, discuss with elders in your community what units were used for measurement of length in the olden days. Also, using the internet, try to find out about the length scales found in excavations of archaeological sites in India. This is a research activity about our rich history of measurement.

Fourth, create a maze using lines of 1 cm, 2 cm and their combination. Part of it has been made for you in the textbook. Now use your imagination and expand it to a size as big as you want. This is a fun creative activity.

Fifth, how tall am I? Stand along a wall and with the help of an adult, mark your height. Repeat it every three months to maintain a height record for yourself and your siblings. This is a great way to track your growth!

Sixth, let us design a fun method for measuring the distance between two places by using a bicycle. Attach a flexible metal strip to the spoke of the front wheel in such a manner that it hits the frame of the bicycle holding the wheel, every time it crosses it and produces a sound. Now ride the bicycle slowly and count the number of times in which sound occurred. The number will give you the number of turns of your wheel made. Now measure the length of the outer boundary of the wheel using a string. Multiply this length by the number of turns of the wheel. This is the distance you travelled. Such methods are actually used to measure the distance for road-running races. Try to find out about a 'Jones Counter' which is attached to a bicycle wheel and is used for measuring distances. This is a fascinating application of measurement in real life!

Now students, we have covered the entire chapter. Let me give you a complete summary of everything we have learned today.

In this chapter, we learned that:

The International System of Units, also known as SI units, has been adopted by countries all over the world as standard units of measurement. This helps in maintaining consistency and avoiding confusion.

The SI unit of length is metre, and its symbol is m.

We learned the relationships between different units of length: 1 kilometre equals 1000 metres 1 metre equals 100 centimetres 1 centimetre equals 10 millimetres

When distance is stated with respect to a fixed object or point, this point is called a reference point. Reference points are very important in describing position and motion.

An object is said to be in motion if its position changes with respect to a reference point with time. If the position does not change with time, the object is at rest.

We learned about three types of motion: When an object moves along a straight line, its motion is called linear motion. When an object moves along a circular path, its motion is called circular motion. When any object moves to and fro about any fixed position, its motion is called oscillatory motion.

We also learned the correct way to measure length - placing the scale properly, keeping the eye at the correct position, and handling broken scales correctly.

We learned how to measure curved lines using a thread and then measuring the thread.

We understood that handspans and other body parts are not reliable for measurement because they vary from person to person, which is why standard units are necessary.

We explored the rich history of measurement systems in ancient India, including units like angula, dhanusa, and yojana.

We learned about periodic motion - when an object repeats its path after a fixed interval of time. Both circular and oscillatory motions are periodic in nature.

We practiced various exercises and activities to reinforce our learning.

Students, measurement and motion are fundamental concepts in science that you will use throughout your life. Whether you become a scientist, an engineer, a doctor, or anything else, you will need to measure things accurately and understand motion. So keep practicing, keep exploring, and keep asking questions!

That brings us to the end of today's lesson. Thank you for listening so attentively. Keep studying hard and I will see you in the next lesson. Goodbye, students!