Class 6 Science Notes Chapter 10 (Motion and Measurement of Distances) – Science Book

Detailed Notes with MCQs of Chapter 10: Motion and Measurement of Distances. This is an important foundational chapter, not just for your science understanding but also because concepts related to measurement and motion often appear in various government exams in the general science or general awareness sections. Pay close attention to the definitions and examples.

Chapter 10: Motion and Measurement of Distances - Detailed Notes

1. The Story of Transport:

• Early Methods: Humans initially travelled on foot. Later, they used animals (horses, camels, bullocks) and simple structures like boats and rafts for water transport.
• Invention of the Wheel: This was a major revolution, leading to carts and chariots pulled by animals, making land transport much easier and faster.
• Steam Engine: Led to the development of trains and steamships in the 18th and 19th centuries.
• Modern Transport: Includes automobiles (cars, buses), aeroplanes, electric trains, monorails, supersonic jets, and spacecraft. This evolution highlights the need for measuring distances accurately.

2. Measurement:

• What is Measurement? Measurement means comparing an unknown quantity with a known fixed quantity. This known fixed quantity is called a unit. The result of a measurement is expressed in two parts: a number and a unit (e.g., 5 metres).
• Need for Measurement: Essential in daily life (tailoring clothes, buying vegetables, construction) and scientific experiments.
• Non-Standard Units:
  • Early methods used body parts: Hand span, cubit (elbow to fingertip), footstep, fathom.
  • Limitations: These units vary from person to person, leading to inconsistency and confusion. They are not reliable for accurate or universal measurement.
• Standard Units:
  • Units that have a fixed value and do not change from person to person or place to place are called standard units.
  • Need for Standard Units: To ensure uniformity and avoid disputes in trade, science, and daily life.
  • SI Units (International System of Units): Globally accepted system of standard units.
    • The SI unit of length is the metre (m).
    • For convenience, we use smaller and larger units:
      • 1 metre (m) = 100 centimetres (cm)
      • 1 centimetre (cm) = 10 millimetres (mm)
      • 1 kilometre (km) = 1000 metres (m)
  • Choosing the Right Unit: Use appropriate units depending on the length being measured (e.g., mm or cm for pencil length, m for room length, km for distance between cities).

3. Correct Measurement of Length:

• Using a Measuring Scale (Ruler):

  • Place the scale in contact with the object along its length.
  • Start measurement from the zero (0) mark of the scale.
  • If the zero mark is broken or unclear, start from another full mark (e.g., 1 cm mark) and subtract this value from the final reading. (Example: If you start at 1 cm and end at 8.5 cm, the length is 8.5 - 1 = 7.5 cm).
  • Eye Position: Your eye must be positioned directly above the point where the measurement is to be taken to avoid parallax error (seeing different readings from different angles).

• Measuring a Curved Line:

  • Using a Thread: Place a thread along the curved line, starting from one end. Mark the start and end points on the thread. Straighten the thread and measure its length using a scale.
  • Using a Divider: Open the divider to a small, convenient length. Place one point at the start of the curve and swing the other point to mark the curve. 'Walk' the divider along the curve, counting the number of steps. Measure the length of one step and multiply by the number of steps. Measure any remaining part separately. (Less common method now, thread method is simpler).

4. Motion:

• Rest: An object is said to be at rest if its position does not change with respect to its surroundings over time. (e.g., a book on a table, a house).
• Motion: An object is said to be in motion if its position changes with respect to its surroundings over time. (e.g., a flying bird, a moving car, hands of a clock).
• Motion is Relative: An object can be in motion relative to one thing and at rest relative to another. (e.g., A passenger inside a moving bus is at rest relative to other passengers but in motion relative to a tree outside).

5. Types of Motion:

• Rectilinear Motion:

  • Motion along a straight line.
  • Examples: A car moving on a straight road, soldiers in a march past, a stone falling freely from a height, a sprinter running on a straight track.

• Circular Motion:

  • Motion of an object such that its distance from a fixed point remains the same. The object moves along a circular path.
  • Examples: Hands of a clock, blades of a rotating fan, a stone tied to a string and whirled around, a point marked on the rim of a rotating wheel, Earth revolving around the Sun (approximately circular).

• Periodic Motion:

  • Motion that repeats itself after regular intervals of time.
  • Examples: Motion of a pendulum (like in an old clock), a child on a swing, strings of a guitar when plucked, heartbeat, revolution of the Earth around the Sun (also circular), rotation of the Earth on its axis (also rotational).

• Rotational Motion:

  • Motion where an object turns or spins about a fixed axis. Different parts of the object move different distances in the same time.
  • Examples: Rotation of the Earth on its axis, a spinning top, blades of a fan (the fan as a whole rotates), a rotating wheel.
  • Note: Circular vs Rotational: In circular motion, the object as a whole moves in a circle (like a car on a circular track). In rotational motion, the object spins around an axis within itself (like a spinning top).

• Combination of Motions: Objects often exhibit more than one type of motion simultaneously.

  • Ball rolling on the ground: Rectilinear (moves forward) + Rotational (spins).
  • Wheel of a moving bicycle: Rotational (spins on axle) + Rectilinear (moves forward).
  • Needle of a sewing machine: Periodic (repeats up-and-down movement) + Rectilinear (moves up and down in a straight line).
  • Earth: Rotational (spins on axis) + Circular/Periodic (revolves around the Sun).

Key Terms:

• Measurement: Comparing an unknown quantity with a known fixed quantity (unit).
• Unit: A known fixed quantity used for measurement.
• Standard Unit: A unit with a fixed value, accepted universally (e.g., metre, kilogram, second).
• SI Units: International System of Units.
• Metre (m): SI unit of length.
• Rectilinear Motion: Motion in a straight line.
• Circular Motion: Motion along a circular path around a fixed point.
• Periodic Motion: Motion that repeats after fixed time intervals.
• Rotational Motion: Motion of an object spinning on its axis.
• Rest: State of an object when its position doesn't change with time relative to surroundings.
• Motion: State of an object when its position changes with time relative to surroundings.
• Parallax Error: Apparent shift in position of an object when viewed from different angles, leading to errors in measurement.

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on the chapter for your practice:

1. Which of the following is NOT a standard unit of measurement?
   a) Metre
   b) Kilogram
   c) Hand span
   d) Second

2. What is the SI unit of length?
   a) Centimetre
   b) Kilometre
   c) Metre
   d) Millimetre

3. 1 kilometre (km) is equal to:
   a) 100 metres
   b) 10 metres
   c) 1000 metres
   d) 10000 metres

4. Motion of a child on a swing is an example of:
   a) Rectilinear motion
   b) Circular motion
   c) Periodic motion
   d) Rotational motion

5. A car moving on a straight road exhibits which type of motion?
   a) Circular motion
   b) Periodic motion
   c) Rotational motion
   d) Rectilinear motion

6. To measure the length of a curved line, the most appropriate device from the following would be:
   a) Only a measuring scale
   b) A thread and a measuring scale
   c) A protractor
   d) A compass

7. While measuring length using a ruler, the eye should be positioned:
   a) To the left of the reading point
   b) To the right of the reading point
   c) Directly above the reading point
   d) At any comfortable angle

8. The motion of the blades of an electric fan is an example of:
   a) Rectilinear motion
   b) Only Periodic motion
   c) Rotational motion
   d) Only Gravitational motion

9. A rolling ball on the ground shows:
   a) Only Rectilinear motion
   b) Only Rotational motion
   c) Both Rectilinear and Rotational motion
   d) Only Circular motion

10. Which of the following is an ancient unit of measurement based on body parts?
    a) Metre
    b) Cubit
    c) Kilogram
    d) Litre

Answer Key for MCQs:

1. c) Hand span
2. c) Metre
3. c) 1000 metres
4. c) Periodic motion (It also involves some back-and-forth motion, but the key characteristic is repetition in time)
5. d) Rectilinear motion
6. b) A thread and a measuring scale
7. c) Directly above the reading point
8. c) Rotational motion (The blades rotate around a central axis. It's also periodic).
9. c) Both Rectilinear and Rotational motion
10. b) Cubit

Revise these notes thoroughly. Understanding the difference between types of motion and the importance of standard units is crucial. Good luck with your preparation!