Motion and Measurement of Distance PDF

# Motion and Measurement of Distance ## 7.2 Concept of Distance You must have an idea as to how far you have to go to be able to decide the mode of transport - whether to walk, take a bus, a train, a ship, an airplane, or even a spacecraft - to reach a place. ### Activity 1: Count your steps 1....

# Motion and Measurement of Distance ## 7.2 Concept of Distance You must have an idea as to how far you have to go to be able to decide the mode of transport - whether to walk, take a bus, a train, a ship, an airplane, or even a spacecraft - to reach a place. ### Activity 1: Count your steps 1. Count the number of steps you need to take to go from your room to the kitchen. Now count the number of steps you take when walking from your house to the playground. 2. In which case did you take lesser number of steps? Obviously, as the kitchen is nearer than the playground, the number of steps required is less. 3. It shows that when distance is less, you have to travel less. ## Intext Questions 1. Name any five modes of transport that you see in your daily life. 2. What are the usual modes of transport in small villages? 3. Name some animals that can be domesticated for carrying loads. 4. Why is it necessary for us to know the approximate distance to be travelled before starting a journey? ## 7.3 Measurement The answer to "How much" or "How many" can be obtained either by measuring or by counting. Size matters! If CDs were made of different sizes, you would not be able to play them on a single player. Similarly, if your dress was stitched to someone else's size, it would not fit you. ## 7.1 Development of Transport The process of travelling and moving people or goods from one place to another is called transportation. Transportation takes people to where they want to go and brings to them what they need. No trade is possible without transportation. Prehistoric people used to travel and carry goods on foot as there were no other means of transport known to them. It was only around 5,000 BC that people began the use of animals to haul loads. They domesticated some animals such as horses, bulls and mules to carry them and their goods over long distances. Till then, people used to drag their loads along the ground or carry them on their head. ## 7.4 Standard Units of Measurement The difference and inaccuracy in measurements made by using ancient methods led to the realisation of the need to develop some standard units of measurement. Standard units were needed for the sake of uniformity in measurements all over the world, and for measuring various quantities more accurately. Scientists of different countries developed their own systems for measuring, which were again not similar. The metric system was the first standard system of units of measurements. This was first adopted by France in 1791. Over the centuries, many variants to this system were adopted by different nations. ## Intext Questions 1. What is measurement? 2. Name the two types of measurements. 3. Name three ancient methods of measurement. 4. What is the drawback in measuring the length of a table with a handspan? ## 7.6 Taking Curved and Small Measurements We can measure straight lines/distances with a ruler or measuring tape. But how can we measure curved lines/distances? We can use a thread for such measurements. Perform the following activity: 1. Draw a curved line. Take a thread and tie a knot at its one end. Put it at one end of the line. Place the thread along the curved line, stretching and keeping it tight till you reach the other end. Mark the thread on this point with ink. Now you can measure the distance between the two points with a ruler. This will be the approximate length of the curved line. ## 7.7 Motion You must have noticed the movement of different objects around you. You can see the motion of a car on a road, a ceiling fan, etc. In some cases, however, you may not notice the movement of the object. For example, the motion of a second hand on a watch is easily visible but the hour hand moves very slowly. Its movement is not visible. Similarly, there are certain objects that move so fast that you cannot see them moving (invisible motion). The earth rotating on its axis is also an example of invisible motion. So how can motion be described? Motion occurs when an object changes its location in space. Motion is a relative rather than an absolute term. ## 7.8 Types of Motion We know that motion is an integral part of our everyday life. However, the way in which things move varies from object to object. Let us examine different types of motion that we see in the world around us. **Translatory motion:** Have you observed the motion of a vehicle on a straight or curved road? All parts of the vehicle move at the same speed in the same direction. Such a motion on a straight or curved path is called translatory motion. It can further be classified into two categories - rectilinear and curvilinear motion. **Rectilinear motion:** The motion of a body along a straight line is called rectilinear motion. For example, the motion of a car driven on a straight road, motion of a 100 m sprinter, motion of soldiers on a march past, etc. **Curvilinear motion:** When a body changes its position with respect to time on a curved path, then its motion is called curvilinear motion. For example, motion of a train along a curved track on hills. **Rotational motion:** Motion in which a body moves around an axis and different parts of the body cover different distances in a given time interval. For example, consider a rotating top, the outer part and inner part of the top cover different distances. Inner part covers lesser distance than the outer part during the same time interval. Also the top seems to be rotating around an imaginary line passing through its centre. Thus, the motion of a rotating top is rotational motion. Hands of a clock, rotation of the earth on its axis, wheels of a bullock cart, and the blades of a fan are some examples of rotational motion. **Circular motion:** There is another kind of motion which seems like rotational motion, but if you look closely you will find the body moves around a fixed object or point which lies outside the moving body. The body moves along a circular path around this fixed object or point. Such a motion is called circular motion. In this kind of motion, the position of moving body changes continuously with time. Take a small ball, tie a thread to it and whirl it with your hand. What do you observe? The ball moves in a circular path. You might have seen that the needle of a compass is fixed while a pencil moves to trace a path called circular path. Motion of the earth and other planets around the sun in the Solar System represents circular motion. Motion of the moon around the earth is another example of circular motion. **Periodic motion:** Motion which repeats itself after regular time intervals is called periodic motion. Periodic motion can be both circular as well as to and fro' motion. Consider the motion of a swing in a playground. You will notice that the swing moves backward and forward in air and this up and down movement is repeated periodically, i.e., after regular time intervals. Similarly, the motion of a pendulum of a clock and a water wheel is also periodic. You know that the earth rotates about its axis and completes one rotation in 24 hours. The earth also completes one revolution around the sun in 365 days. Hence, rotation and revolution of the earth are both periodic motions. ## Drawbacks Measuring units which were based on the length of a person’s body parts were not accurate and failed because all people were not of the same size. In modern measuring systems, measuring tools consist upon by the users of the system. **Measuring units which were based on the length of a person’s body parts were not accurate and failed because all people were not of the same size. In modern measuring systems, measuring tools consist upon by the users of the system.** ## 7.5 Taking Measurement Now, you can repeat Activity-3 using a standard scale and measure the lengths in standard units. If you measure correctly, observations will always be the same irrespective of the person taking the measurements. To get correct measurements, it is also very necessary to measure the objects correctly. ## 7.5 Taking Measurement Now, you can repeat Activity-3 using a standard scale and measure the lengths in standard units. If you measure correctly, observations will always be the same irrespective of the person taking the measurements. To get correct measurements, it is also very necessary to measure the objects correctly. ## Intext Questions 1. What if a person asks you "How much do you weigh?" or "How many brothers and sisters do you have?" The answer to both the questions is a number. The first question is answered by measuring and the second by counting. If you were to make a wooden door for your house, to calculate how much wood will be required to make it. The cost of land is also decided by the total area of the land. **Measurement is the comparison of an unknown quantity with a fixed quantity of the same kind. The fixed quantity is known as the unit of measurement.** Every measurement involves two things: * The unit of measurement. * The number of units the object measures. For example, when we say that the length of a cloth piece is 3 metres, we actually compare the length of the cloth piece (unknown quantity) with a fixed known quantity (metre). Thus, we can say that the unknown quantity is 3 times the known quantity and is written as 3m. Here, measurement has two parts, a number (3) and a fixed quantity (metre). Metre is the unit of measurement in this case. **Measurement of length and size of objects ** Measuring the size of an object or space involves three types of measurements: 1. Length or distance 2. Area 3. Volume We will study length in this chapter. ## Intext Questions 1. What is measurement? 2. Name the two types of measurements. 3. Name three ancient methods of measurement. 4. What is the drawback in measuring the length of a table with a handspan? ## 7.4 Standard Units of Measurement The difference and inaccuracy in measurements made by using ancient methods led to the realisation of the need to develop some standard units of measurement. Standard units were needed for the sake of uniformity in measurements all over the world, and for measuring various quantities more accurately. Scientists of different countries developed their own systems for measuring, which were again not similar. The metric system was the first standard system of units of measurements. This was first adopted by France in 1791. Over the centuries, many variants to this system were adopted by different nations. More recently, SI system of units, i.e., International System of Units, was adopted as the standard system for measurement in France in 1960, at the General Conference of Weights and Measures. The SI system is the modern form of the old metric system and is now accepted and used worldwide. As per the SI system, standard units for the measurement of basic quantities are: 1. Length - metre (m). 2. Mass - kilogram (kg). 3. Time - second (s). 4. Temperature - kelvin (K). Under the SI system, length or distance is measured in metre. Although, metre is appropriate to measure the length of a cloth, a room, any furniture or area, etc., it won’t be convenient to express the distance between two cities in metres. Can we express the width of an eraser appropriately in metre? Not because one measurement is very large (thousands of metres) and the other is very small (1/1000 of a metre). Therefore, to measure smaller objects/distances, smaller units in metric system, such as millimetre (mm), centimetre (cm) and decimetre (dm) are used. For measuring larger distances, kilometre (km) is used. 1km = 1000m 1m = 100cm 1cm = 10mm Q.1 A tree stands tall at 2350mm. Express its height in metres and centimetres. A.1 We know that: * 1cm = 10mm or 1mm = 1/10cm * 1m = 100cm or 1cm = 1/100m Therefore 2350mm = 2350/10 cm Also 235cm = 235/100cm = 2.35m Height of the tree is 235cm or 2.35m or 2m and 35cm. Q.2 Class 6 students were going for a picnic to a nearby place. The place was at a distance of 33km from the school. Calculate this distance in metres as well as in centimetres. A.2 * 1km = 1000m * 1m =100cm Distance of the picnic place = 33km 33km = 33 x 1000m = 33,000m 33000m = 33000 x 100cm = 33,00,000cm Distance of the picnic place from the school is 33,000m or 33,00,000cm. ## 7.6 Taking Curved and Small Measurements We can measure straight lines/distances with a ruler or measuring tape. But how can we measure curved lines/distances? We can use a thread for such measurements. Perform the following activity: 1. Draw a curved line. Take a thread and tie a knot at its one end. Put it at one end of the line. Place the thread along the curved line, stretching and keeping it tight till you reach the other end. Mark the thread on this point with ink. Now you can measure the distance between the two points with a ruler. This will be the approximate length of the curved line. ## 7.7 Motion You must have noticed the movement of different objects around you. You can see the motion of a car on a road, a ceiling fan, etc. In some cases, however, you may not notice the movement of the object. For example, the motion of a second hand on a watch is easily visible but the hour hand moves very slowly. Its movement is not visible. Similarly, there are certain objects that move so fast that you cannot see them moving (invisible motion). The earth rotating on its axis is also an example of invisible motion. So how can motion be described? Motion occurs when an object changes its location in space. Motion is a relative rather than an absolute term. An object may be in motion with respect to another object but it may be stationary with respect to a third object. For example, you are sitting in a train and pass a person standing along the tracks. That person will see you and everyone else on the train as being in motion. But the person sitting next to you on the train will be stationary with respect to you. Objects that do not change their positions are said to be at rest. Even as you sit reading this page, you are moving because the earth is rotating on its axis. In addition, the sun, the earth and the rest of the planets in our Solar System are also in motion due to the movement of our galaxy within the universe. ## 7.8 Types of Motion We know that motion is an integral part of our everyday life. However, the way in which things move varies from object to object. Let us examine different types of motion that we see in the world around us. **Translatory motion:** Have you observed the motion of a vehicle on a straight or curved road? All parts of the vehicle move at the same speed in the same direction. Such a motion on a straight or curved path is called translatory motion. It can further be classified into two categories - rectilinear and curvilinear motion. **Rectilinear motion:** The motion of a body along a straight line is called rectilinear motion. For example, the motion of a car driven on a straight road, motion of a 100 m sprinter, motion of soldiers on a march past, etc. **Curvilinear motion:** When a body changes its position with respect to time on a curved path, then its motion is called curvilinear motion. For example, motion of a train along a curved track on hills. **Rotational motion:** Motion in which a body moves around an axis and different parts of the body cover different distances in a given time interval. For example, consider a rotating top, the outer part and inner part of the top cover different distances. Inner part covers lesser distance than the outer part during the same time interval. Also the top seems to be rotating around an imaginary line passing through its centre. Thus, the motion of a rotating top is rotational motion. Hands of a clock, rotation of the earth on its axis, wheels of a bullock cart, and the blades of a fan are some examples of rotational motion. **Circular motion:** There is another kind of motion which seems like rotational motion, but if you look closely you will find the body moves around a fixed object or point which lies outside the moving body. The body moves along a circular path around this fixed object or point. Such a motion is called circular motion. In this kind of motion, the position of moving body changes continuously with time. Take a small ball, tie a thread to it and whirl it with your hand. What do you observe? The ball moves in a circular path. You might have seen that the needle of a compass is fixed while a pencil moves to trace a path called circular path. Motion of the earth and other planets around the sun in the Solar System represents circular motion. Motion of the moon around the earth is another example of circular motion. **Periodic motion:** Motion which repeats itself after regular time intervals is called periodic motion. Periodic motion can be both circular as well as to and fro' motion. Consider the motion of a swing in a playground. You will notice that the swing moves backward and forward in air and this up and down movement is repeated periodically, i.e., after regular time intervals. Similarly, the motion of a pendulum of a clock and a water wheel is also periodic. You know that the earth rotates about its axis and completes one rotation in 24 hours. The earth also completes one revolution around the sun in 365 days. Hence, rotation and revolution of the earth are both periodic motions.