MEASUREMENT OF LENGTH AND MOTION : Class 6 : Science
1. Measurement of Length
Measurement means comparing an unknown quantity with a standard unit.
The SI unit of length is metre (m).
Smaller units: millimetre (mm), centimetre (cm); Larger units: kilometre (km).
Instruments to measure length: ruler, metre scale, measuring tape, Vernier calipers (for small objects).
Precautions while using a scale:
Place scale along the object.
Avoid gaps or broken edges.
Keep eyes vertically above the reading (to prevent parallax error).
2. Measurement of Curved Lines
Cannot be measured directly with a ruler.
Use a thread to trace the curve and then measure on a scale.
Or use a divider to measure step by step.
3. Motion and Rest
An object is at rest if it does not change its position with time.
An object is in motion if it changes position with time.
4. Types of Motion
Rectilinear motion – motion along a straight line (car on road).
Circular motion – motion around a fixed point (fan blades, clock hands).
Rotational motion – whole object rotates around its axis (earth spinning).
Periodic motion – motion that repeats at regular intervals (swing, pendulum, heartbeat).
5. Measurement of Distance and Time in Motion
Distance: length of path travelled by an object.
Time is measured using clocks and stopwatches.
Uniform motion – covers equal distances in equal intervals of time.
Non-uniform motion – covers unequal distances in equal intervals of time.
SHORT QUESTIONS & ANSWERS (1 MARK)
1.What is measurement?
Comparing an unknown quantity with a standard unit.
2.What is the SI unit of length?
Metre (m).
3. 1 kilometre = ? metres
1000 metres.
4. 1 metre = ? centimetres
100 centimetres.
5.Which instrument is commonly used to measure length?
A ruler or metre scale.
6.Which instrument is used to measure cloth in a shop?
Measuring tape.
7.What is parallax error?
Error due to not keeping the eye vertically above the scale while reading.
8.How can we avoid parallax error?
By keeping the eye exactly above the reading point.
9.Which instrument is used to measure very small lengths?
Vernier calipers.
10.Which method is used to measure curved lines?
Using a thread or divider.
11.When is an object said to be at rest?
When it does not change position with time.
12.When is an object said to be in motion?
When it changes position with time.
13.Name the motion of a car moving on a straight road.
Rectilinear motion.
14.Name the motion of a fan blade.
Circular motion.
15.Earth spinning on its axis shows which motion?
Rotational motion.
16.A pendulum shows which type of motion?
Periodic motion.
17.The motion of the moon around the earth is of what type?
Circular motion.
18.The hands of a clock show which type of motion?
Circular motion.
19.The wheels of a bicycle show which type of motion?
Rotational motion.
20.Heartbeat shows which type of motion?
Periodic motion.
21.What is distance?
The length of the path covered by an object.
22.Which instrument measures time?
Clock or stopwatch.
23.What is uniform motion?
Motion in which equal distances are covered in equal time intervals.
24.What is non-uniform motion?
Motion in which unequal distances are covered in equal time intervals.
25.A train moving at the same speed shows which motion?
Uniform motion.
26.A car moving in traffic shows which motion?
Non-uniform motion.
27.Which unit is used to measure long distances between cities?
Kilometres.
28.Which unit is used to measure the thickness of a coin?
Millimetre or smaller units.
29.Which type of motion does a swing show?
Periodic motion.
30.What is the standard unit of time in SI?
Second (s).
31.Which type of motion does a child sliding down a slide show?
Rectilinear motion.
32.Which type of motion does the Earth around the Sun show?
Circular motion.
33.The blades of a windmill show which type of motion?
Rotational motion.
34.A sewing machine needle shows which type of motion?
Periodic motion.
35.The motion of the tip of a moving clock hand is?
Circular motion.
36.A soldier standing still is in which state?
Rest.
37.The motion of a cricket ball hit by a bat is?
Rectilinear motion.
38.The motion of the washing machine drum is?
Rotational motion.
39.The motion of a swing in a park is?
Periodic motion.
40.The distance between two cities is measured in which unit?
Kilometres (km).
LONG QUESTION & ANSWER (5–10 MARKS)
1.What is measurement? Why do we need standard units of measurement?
Measurement is the process of comparing an unknown quantity with a known standard quantity. We need standard units so that measurement is the same everywhere and avoids confusion.
2.What is the SI unit of length? Write its multiples and sub-multiples.
The SI unit of length is metre (m).
Multiples: 1 km = 1000 m
Sub-multiples: 1 m = 100 cm = 1000 mm
Name the different instruments used to measure length. Give examples.
Ruler/metre scale – used in school.
Measuring tape – used in shops to measure cloth.
Vernier calipers – used in laboratories to measure small objects.
Thread/divider – to measure curved lines.
3.What is parallax error? How can it be avoided?
Parallax error happens when the eye is not kept exactly above the mark while taking a reading, which gives wrong measurements.
It can be avoided by keeping the eye vertically above the point of measurement.
4.How can you measure the length of a curved line?
Place a thread along the curved line.
Mark the thread from start to end.
Stretch the thread on a ruler.
The reading gives the length of the curved line.
5.Explain with examples the use of different measuring tools in daily life.
Cloth is measured with measuring tape.
Books with a ruler.
Thickness of a coin with vernier calipers.
Distance between two cities with kilometre unit.
6.Define rest and motion with examples.
An object is at rest if it does not change position with time (e.g., a tree).
An object is in motion if it changes position with time (e.g., a moving car).
7.Differentiate between rectilinear motion and circular motion with examples.
Rectilinear motion: Object moves in a straight line (a car on a straight road).
Circular motion: Object moves in a circular path (hands of a clock).
8.What is rotational motion? Give two examples.
When an object rotates about its axis, it is rotational motion.
Examples: A spinning top, rotating wheel of a bicycle.
9.What is periodic motion? Give three examples.
Motion that repeats at equal intervals of time.
Examples: Pendulum of a clock, swing in a park, heartbeat.
10.Write the difference between uniform and non-uniform motion with examples.
Uniform motion: Equal distances covered in equal intervals of time (a train moving at constant speed).
Non-uniform motion: Unequal distances in equal intervals (a car in traffic).
11.What is distance? How is it measured?
Distance is the length of the path covered by an object. It is measured using ruler, metre scale, tape, or kilometre for long distances.
12.What is time? What is the SI unit of time?
Time tells us how long an event takes place. Its SI unit is second (s).
13.How can time be measured? Give examples of devices.
Sundial – old method.
Sand clock – traditional.
Mechanical clocks, wrist watches, stopwatches – modern methods.
14.Give five examples of periodic motion in daily life.
Pendulum of a clock, rotation of Earth, swing, heartbeat, and motion of a drum in washing machine.
Explain rectilinear, circular, rotational and periodic motions with suitable daily life examples.
Rectilinear: A train moving on straight track.
Circular: Hands of a clock.
Rotational: Fan blades.
Periodic: Swing.
15.What is the difference between motion and rest?
Rest: Object does not change position (a parked car).
Motion: Object changes position (a running car).
16.Write four examples of rectilinear motion.
Train on a straight track, child sliding on slide, cricket ball rolling on ground, soldier marching straight.
17.Write four examples of circular motion.
Hands of a clock, moon around Earth, giant wheel, blades of a fan.
18.Write four examples of rotational motion.
Spinning top, wheel of a cycle, Earth rotating, washing machine drum.
19.Write four examples of periodic motion.
Swing, pendulum, heartbeat, motion of planets.
20.Explain the motion of a pendulum.
A pendulum moves back and forth around a fixed point. The motion repeats after equal intervals of time, hence it is periodic motion.
21.Why is distance between two cities measured in kilometre and not in metre?
Because the distance is very large, kilometre is a bigger unit and convenient to use.
22.Why is a thread used to measure a curved line instead of a ruler?
Because a ruler is straight, while a thread can bend and fit along a curve.
23.Why do we need standard units of measurement?
So that measurements are the same everywhere in the world and avoid confusion.
24.What is meant by standard unit? Give examples.
A fixed quantity used worldwide for measurement. Examples: metre for length, kilogram for mass, second for time.
25.Why do we use kilometre instead of metre to measure long distances?
Because metre is too small; kilometre is a convenient larger unit for long distances.
26.Explain with examples how the same object can be at rest and in motion.
A passenger in a moving bus is at rest with respect to other passengers, but in motion with respect to trees outside.
27.List differences between circular motion and rotational motion with examples.
Circular motion: Object moves around another object (moon around Earth).
Rotational motion: Object spins on its own axis (Earth rotating).
28.Explain the motion of Earth in detail.
Earth rotates on its axis – rotational motion.
Earth revolves around the Sun – circular motion.
Both together cause day-night and seasons.
MCQS CHOOSE THE CORRECT OPTION
The SI unit of length is
a) centimetre
b) kilometre
c) metre
d) millimetre
Answer: c) metre
1 kilometre is equal to
a) 1000 metres
b) 100 metres
c) 10,000 metres
d) 100 cm
Answer: a) 1000 metres
Which instrument is used to measure the length of a curved line?
a) Ruler
b) Thread
c) Protractor
d) Compass
Answer: b) Thread
What should be avoided while taking length measurement with a scale?
a) Using a metal scale
b) Viewing from the side (parallax error)
c) Using centimetres
d) Placing scale on object
Answer: b) Viewing from the side (parallax error)
Which of the following is NOT a type of motion?
a) Rectilinear motion
b) Circular motion
c) Static motion
d) Periodic motion
Answer: c) Static motion
A child swinging on a swing shows which type of motion?
a) Rectilinear
b) Circular
c) Periodic
d) Rotational
Answer: c) Periodic
The motion of the earth around the sun is
a) Rotational motion
b) Rectilinear motion
c) Circular motion
d) Periodic motion
Answer: d) Periodic motion
The motion of a spinning top is
a) Circular
b) Rotational
c) Rectilinear
d) Periodic
Answer: b) Rotational
Which device is used to measure time in experiments?
a) Ruler
b) Stop-watch
c) Thermometer
d) Protractor
Answer: b) Stop-watch
A fan blade shows which type of motion?
a) Rectilinear
b) Rotational
c) Periodic
d) Rectangular
Answer: b) Rotational
The pendulum of a clock shows
a) Rectilinear motion
b) Circular motion
c) Periodic motion
d) Uniform motion
Answer: c) Periodic motion
An object is said to be at rest if
a) It moves continuously
b) It does not change its position with time
c) It rotates around its axis
d) It vibrates
Answer: b) It does not change its position with time
Motion in a straight line is called
a) Circular motion
b) Rectilinear motion
c) Periodic motion
d) Rotational motion
Answer: b) Rectilinear motion
Which is an example of rectilinear motion?
a) Train on straight track
b) Spinning wheel
c) Swinging pendulum
d) Earth rotating
Answer: a) Train on straight track
Motion of the moon around the earth is
a) Rotational
b) Periodic
c) Rectilinear
d) Non-uniform
Answer: b) Periodic
Distance is measured in
a) Seconds
b) Metres
c) Kilograms
d) Litres
Answer: b) Metres
Which of these represents uniform motion?
a) A car moving at a constant speed
b) A car stopping and starting
c) A child swinging
d) A clock pendulum
Answer: a) A car moving at a constant speed
Which of these is an example of non-uniform motion?
a) Earth’s rotation
b) A boy running on a zigzag path
c) Clock hands
d) Train at constant speed
Answer: b) A boy running on a zigzag path
Which unit is NOT used to measure length?
a) Centimetre
b) Millimetre
c) Litre
d) Kilometre
Answer: c) Litre
The length of a cricket pitch is usually measured in
a) Centimetres
b) Millimetres
c) Metres
d) Kilometres
Answer: c) Metres
The correct method to measure a pencil with a scale is
a) Place it away from scale
b) Align it with zero mark
c) Start from 1 cm
d) Hold scale in air
Answer: b) Align it with zero mark
Which type of motion do the hands of a clock show?
a) Rectilinear
b) Circular
c) Periodic
d) Both circular and periodic
Answer: d) Both circular and periodic
A bus moving on a straight road represents
a) Rectilinear motion
b) Periodic motion
c) Circular motion
d) Rotational motion
Answer: a) Rectilinear motion
The motion of the earth spinning on its axis is
a) Rectilinear motion
b) Circular motion
c) Rotational motion
d) Periodic motion
Answer: c) Rotational motion
Which of these is an example of periodic motion in daily life?
a) Falling of a ball
b) Swinging of a pendulum
c) Walking of a person
d) Movement of train
Answer: b) Swinging of a pendulum
The length of a classroom is best measured in
a) Millimetres
b) Centimetres
c) Metres
d) Kilometres
Answer: c) Metres
Which of these devices does NOT measure length?
a) Ruler
b) Measuring tape
c) Stopwatch
d) Metre scale
Answer: c) Stopwatch
What kind of motion is shown by the second’s hand of a clock?
a) Rectilinear
b) Periodic and circular
c) Rotational
d) Non-uniform
Answer: b) Periodic and circular
Which of the following is correct?
a) 1 cm = 10 mm
b) 1 m = 10 cm
c) 1 km = 100 m
d) 1 mm = 100 cm
Answer: a) 1 cm = 10 mm
Which is the most appropriate unit to measure the distance between two cities?
a) Metre
b) Centimetre
c) Millimetre
d) Kilometre
Answer: d) Kilometre
