Class -6, Science, Chapter:- 10 (Motion And Measurement of Distances) Notes, NCERT Solutions & Frequently Asked Questions

  Science

Class:-6, Chapter:- 10

(Motion And Measurement of  Distances)

Notes, NCERT Solutions & Frequently Asked Questions

-- Notes --

⭐ Means of transport:- Ever since ancient times, humans have devised different means of transport to travel from one place to another.

• They designed boats that resemble the shapes of animals living in water to travel across water bodies. 

• They invented the wheel, which led to inventions like carts and other animal driven modes of transport.

• During the beginning of the 19th-century humans designed the steam engine, which was followed by automobiles and motorised vehicles.

⭐ Measuring Length:-

• Distance:- Distance is the measure of how far or long something is. E.g.: the length of a table, or a soccer field or, how far is Mumbai from Delhi?

• Length:- Length can be measured in terms of a unit. A unit is a comparison of an unknown quantity with that of a known quantity. It is required to establish a common standard or convention in order to make calculations and analysis easier worldwide.

⭐ Traditional ways of measuring lengths:- Traditional methods of measuring length were the use of the length one’s foot or other body parts. But, was inconsistent since this varies from person to person and lacks uniformity.

⭐ Standard Units:- Scientists from all over the world have accepted a common standard units of measurement.

• The International System of Units (S.I unit) was set up as the convention for measurement worldwide.

• A metre is the SI unit of length. It has 100 equal divisions called as centimetres.

• To measure large distances we use kilometres. 1 Km = 1000 metres.

⭐ Zero error and Correct way to measure length:- Scale must be in contact with the object being measured.

• If scales are broken or the zero mark is not visible, it can lead to a zero error. Then measuring from a different mark must be carried out.

• The correct reading will be obtained by subtracting the value from the full mark considered as the zero.

• While measuring the eye must be exactly above the point where the measurement is to be taken, in order to avoid parallax errors.

⭐ Errors in Measurements:-

• Parallax:- Parallax is the displacement or the change in the apparent position of the object when viewed from two different points of views. This type of error while measuring is called as parallax error.

⭐ How to Measure the Length a Curved Line:- Curved lengths cannot be measured using metre scales.

• A string or a thread can be used to measure curved lines by creating a knot at one end and keeping that at the beginning, one can trace the curved line.

• Then this length can be stretched out and measured with the help of a metre scale.

• A measuring tape can be used to find lengths of curved objects. E.g. girth of a tree trunk, or length of a snake.

⭐ Motion :- If there is change in the position of an object, then the object is said to be in motion. 

⭐ Types of motion:- 

• When a body is moving in a straight line path, it is called Rectilinear Motion. E.g. : a coin falling from a building, or a sprinter running a 100 metre race.

• When an object is following a circular path of motion, it is called as Circular Motion. E.g. the moon revolving around the earth.

• When an object moves to and fro from a mean or constant position or repeats the motion, it is called as Periodic Motion. E.g. : a pendulum, or a race car taking laps of a circuit.

⭐ Time:- Time is the unit that measures how long it takes to do anything. Distance is measured with respect to time.

• If an object is moving with some speed ‘s’ for a time interval ‘t’, then the distance 'u' covered in that time will be

 u = s × t. 

-- NCERT Solutions --

Questions 1.- Give two examples each, of modes of transport used on land, water and air.

Solution:-

• Land:- Train, Bus

• Water:- Ship, Boat

• Air:- Helicopter, Aeroplane

Question 2.- Fill in the blanks:

(i) One metre is ______________ cm.

(ii) Five kilometre is ______________ m.

(iii) Motion of a child on a swing is ______________.

(iv) Motion of the needle of a sewing machine is ______________.

(v) Motion of wheel of a bicycle is______________.

Solution:-

(i) 100

(ii) 5000

(iii) periodic

(iv) periodic

(v) circular

Question 3.- Why can a pace or a footstep not be used as a standard unit of length?

Solution:- Pace or a footstep cannot be used as a standard unit of length because it varies from person to person.

Question 4.- Arrange the following lengths in their increasing magnitude: 1 metre, 1 centimetre, 1 kilometre, 1 millimetre.

Solution:- 1 millimetre, 1 centimetre, 1 metre, 1 kilometre

Question 5.- The height of a person is 1.65 m. Express it into cm and mm.

Solution:- 1.65= 165 cm = 1650 mm

Question 6.- The distance between Radha’s home and her school is 3250 m. Express this distance into km.

Solution:- 1km = 1000 m

Hence 3250 m = 3.25 kms

Question 7.- While measuring the length of a knitting needle, the reading of the scale at one end is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle?

Solution:- Length of needle = 33.1 – 3 = 30.1 cm

Question 8.- Write the similarities and differences between the motion of a bicycle and a ceiling fan that has been switched on.

Solution:-

• Similarities – The blades of a fan and the wheels of a bicycle shows circular motion

• Differences- Bicycle move in rectilinear motion, but the fan does not move in circular motion.

Question 9.- Why would you not like to use a measuring tape made of an elastic material like rubber to measure distance? What would be some of the problems you would meet in telling someone about a distance you measured with such a tape?

Solution:- An elastic measuring tape will not give accurate measurement as it stretches in length and reduces in size when stretched. When we express measurement taken with elastic tape, we have to tell whether the tape was stretched. If yes, how much. Hence it is very difficult to tell the measurement taken from an elastic tape.

Question 10.- Give two examples of periodic motion.

Solution:-

a) A needle of a sewing machine

b) Pendulum

-- Frequently Asked Questions --

Question 1.- Why do we need standard unit for measurement?

Answer:- We need standard unit for measurement to make our judgement more reliable and accurate. For proper dealing, measurement should be same for everybody. Thus there should be uniformity in measurement. For the sake of uniformity we need a common set of units of measurement, which are called standard units. Nowadays SI units are used in science and technology almost universally.

Question 2.- State two precautions to be observed while measuring length with the help of a metre scale.

Answer:- Two precautions are:

(i) The initial point of distance must coincide with the zero reading of metre scale.

(ii) The eye should be kept in line with the point of measurement.

Question 3.- Define rest and motion.

Answer:- The objects which do not change their positions with time are said to be at rest. The objects which change their positions with time are said to be in motion.

Question 4.- Define the term standard unit.

Answer:- The unit that could be used everywhere as a basic unit of measurement is called a standard unit.

Question 5.- How can a measured length be expressed?

Answer:- Each measurement has:

(i) A number describing the numerical value.

(ii) The unit in which that quantity is measured.

- By Durgesh Pandey