Science Notes - Class 6 - Motion and Measurement PDF

DELHI PUBLIC SCHOOL RANIPUR, HARIDWAR SUBJECT: SCIENCE, CLASS-VI NOTES CHAPTER-10 MOTION AND MEASUREMENT Motion: If an object is changing its position with respect to time and its fixed surroundings then the...

DELHI PUBLIC SCHOOL RANIPUR, HARIDWAR SUBJECT: SCIENCE, CLASS-VI NOTES CHAPTER-10 MOTION AND MEASUREMENT Motion: If an object is changing its position with respect to time and its fixed surroundings then the object is said be in motion. Birds flying in the sky, fish swimming in water, walking, riding cycle are some examples which demonstrate motion. Rest: If an object is not changing its position with respect to the time and its fixed surrounding then the object is said be in rest. A truck parked along a road, walls of our room, furniture placed in our house are some examples to demonstrate the objects in rest. CONCEPT OF RELATIVE MOTION: An object can be in rest for someone and can also be in motion for someone else. For example, if we are using an escalator, we are in rest for someone standing next to us but for other people, standing away from the escalator, we are in motion. Suppose we are moving in a train then we are at rest for a co- passenger but for someone standing outside the train, we are in motion. TYPES OF MOTION: 1. Rectilinear motion: The type of motion in which an object moves in a straight line is called rectilinear motion. Ex: A boy is cycling along a straight road, motion of a person in an elevator, falling of fruit from a tree naturally. 2. Curvilinear motion: - The type of motion in which an object moves in a curved path is called curvilinear motion. Ex: A car taking U turn, motion of a child in a roller coaster ride. 3. Circular motion: - The type of motion in which an object is moving in such a way that it always remains at an equal distance from a fixed point while moving is called circular motion. The fixed point is called the centre of the circle and the fixed distance is called the rad ius of the circle. Ex: A boy is cycling on a path made around a circular park, motion of an artificial satellite around the Earth at a fixed height, motion of a child in a merry go round. 4. Periodic motion:-The type of motion which is repeated after every fixed interval of time is called periodic motion.Ex: Motion of the planets on their axis as well as around the sun, motion of the hands of a clock or motion of the pendulum of a clock. 5. Non periodic motion:- The type of motion that does not repeat itself after a fixed interval of time is called non periodic motion. Ex- A car moving in a crowded road, motion of our body while dancing, swaying of the branches of the trees. 6. Rotational motion:- The motion in which an object rotates on its own axis at a fixed point is called rotational motion. Ex: Rotation of the earth and other planets on their own axis, motion of the ceiling fan, motion of a spinning top.  7. Oscillatory motion-The type of motion in which an object moves to and fro around a fixed point (mean position) is called oscillatory motion. Ex: Motion of the pendulum of a clock, motion of our hands while walking, motion of a pirate ship swing. TWO OR MORE TYPES OF MOTION AT A TIME: An object can demonstrate two or more types of motion at a time. Let us consider a few examples. 1.Motion of a bicycle: If a bicycle is moving on a straight road then it displays rectilinear motion and its wheels show rotational motion. Pedals perform circular motion. 2. Motion of the Earth: Our Earth performs rotational motion as it rotates on its axis and periodic motion as it completes its one rotation (on its axis) always in same period (period of one day) as well as it completes its one revolution around the Sun always in equal time (period of one year). 3. Motion of a child in a Merry Go Round: The motion of a child in a merry go round is circular but and if we consider Merry go round as a whole then it turns on its axle and displays rotational motion also. 4. Pendulum of a clock: The pendulum of a clock displays periodic motion as it repeats its motion after every fixed interval and also oscillatory motion as it moves to and fro around its mean position. Measurement: The comparison of an unknown quantity with respect to a known quantity is called measurement. That known quantity is called the unit of measurement. The result of measurement is expressed in two parts; one part is the number or magnitude and the other part is the unit. For example: 1. Duration of one minute is 60 seconds. Here 60 is the magnitude and Second is the unit. 2. Length of a saree is 5.5 meter. Here 5.5 is the magnitude and Meter is the unit. BE CAREFUL: There is no significance of measurement without unit. We generally see that the students solve the numerical correctly in Mathematics or Science but they forget to write the unit. Let us discuss one example. Suppose in a question it is asked that what is the duration of one day. A student writes it is 24. Now what does 24 mean? Does it mean 24 hours or 24 minutes or 24 seconds? Without unit this answer is incomplete. So never forget to write the unit while solving any numerical. Marks are also deducted for the same. SOME ANCIENT UNITS OF MEASURING DISTANCE:  1. Hand span- It is the distance between the tip of thumb to the tip of little finger in an outstretched palm. 2. Cubit- It i s the distance between the t ip of middle finger and the bottom of our elbow. 3. Yard- It is the distance from chin to the tip of middle finger in an outstretched arm. 4. Pace -The length of one normal walking step. 5. Foot-It is the length of the foot of a person. NEED OF ADOPTING SI UNITS OF MEASUREMENT: Earlier, the people used to take the measurement with the help of their body parts or in different ways as per their convenience. This created confusion in measurement as the sizes of the body parts of different people were different. To avoid this confusion and for the sake of uniformity, French created a system of measurement Known as Système International d’unités. Later on, this system of units was accepted in most of the countries after some modification and was called as International System of Units or SI system of units across world which has a set of seven base or standard units of measurement with the help of which other units can be derived. SOME SI UNITS: Quantity Unit Abbreviation Length Metre m Mass Kilogram kg Time Second s Temperature Kelvin K Electric current Ampere A ADVANTAGE OF USING SI UNITS: We need SI system of units: 1. for the sake of uniformity all over the world in taking measurement which prevents confusion. 2. to make our judgement more reliable and accurate. NOTE: 1kilometre= 1000 metre 1 metre =10 decimetre 1 metre= 100 centimetre 1 metre= 1000milimetre Q: Convert 245.7 km into m, dm and cm. Q: Convert 6500 m into dm, mm and km. Ans : 1km= 1000m Ans: 1m= 10dm So 245.7km= 245.7×1000= 245700m 6500m=6500×10=65000dm Again 1km= 10000dm Again 1m=1000 mm So 245.7 km= 245.7×10000= 2457000cm So 6500m= 6500×1000=6500000mm Again 1km= 100000cm Again 1 km= 1000 m So 245.7 km= 245.7×100000= 24570000cm 6500m= 6500/1000= 6.5km Parallax error: It is the error caused in measurement due to the wrong position of the eye while taking measurement. In the diagram given below A and C are the wrong positions of eye while taking measurement and B is the correct one. If we take measurement from point A then the length of the object may appear to be 10cm, from point C it may appear to be 8cm but from point B it can be measured correctly that is 9cm. HOW CAN WE MEASURE A CURVED LINE? For measuring a curved line, we require a thread and a ruler. 1. Tie a knot at one end of the thread. 2. Place the thread at the beginning of the line and try to measure a small initial portion of the line which is relatively straight. 3. Place your thumb at the other end of the measured portion and measure next straighter portion. 4. Repeat the above step till the end of line is reached. Make a knot at the end of the line. 5. Now, straighten the thread and measure the length between the two knots on a ruler. HOW CAN WE MEASURE THE LENGTH WITH A BROKEN RULER? We can measure the length using a broken ruler by the following way - 1. Take the broken ruler and measure the length with the available readings of the scale. 2. Note down the two readings which you get from the two ends of the object. 3. Now, subtract the smaller reading from the greater reading to get the actual length of the object. Ex: While measuring the length of a knitting needle, the reading of the scale at one end is 3.0cm and it the other end is 33. 1cm.What is the length of the needle? Solution: Reading at first end=3.0cm Reading at last end =33.1cm Length of the needle= reading at last end- reading at first end= 33.1cm-3.0cm=30.1cm