Class 6 Science Notes Chapter 10 (Chapter 10) – Examplar Problem Book

Alright class, let's dive into Chapter 10: 'Motion and Measurement of Distances'. Understanding how things move and how we measure distances is fundamental, not just for science but also for many competitive exams. Pay close attention to the concepts and definitions.

Chapter 10: Motion and Measurement of Distances - Detailed Notes

1. Introduction: The Need for Transport & Measurement

• Humans have always needed to move from one place to another (transport) for food, shelter, trade, etc.
• Early transport involved walking, using animals, and simple boats/rafts made from logs.
• Key Developments in Transport:
  • Invention of the Wheel: A major breakthrough leading to animal-drawn carts, improving land transport significantly.
  • Steam Engine (19th Century): Powered locomotives (trains) and ships, revolutionizing long-distance travel.
  • Modern Transport: Includes automobiles (cars, buses), aeroplanes, electric trains, ships, and spacecraft.
• To build transport, describe journeys, or trade goods, accurately measuring distances became crucial.

2. Measurement and Units

• Measurement: Comparing an unknown quantity with a known, fixed quantity called a unit. The result has two parts: a number and a unit (e.g., 5 metres).
• Ancient Methods of Measurement (Non-Standard Units):
  • Based on body parts: Hand span, Cubit (elbow to fingertip), Footstep, Finger width (Angul).
  • Problem: These units are not reliable because they vary from person to person. This leads to confusion and inaccurate measurements.
• Standard Units: Fixed units of measurement that do not change from person to person or place to place. They ensure uniformity and accuracy.
  • Example: A tailor using a standard measuring tape gets consistent results.
• The International System of Units (SI Units): A globally accepted system of standard units adopted for uniformity in scientific and general measurements.
  • SI Unit of Length: Metre (symbol: m)
• Commonly Used Units of Length & Conversions:
  • 1 Metre (m) = 100 Centimetres (cm)
  • 1 Centimetre (cm) = 10 Millimetres (mm)
  • 1 Kilometre (km) = 1000 Metres (m)
  • Therefore: 1 m = 1000 mm and 1 km = 100,000 cm

3. Correct Measurement of Length

• Accuracy is key in measurement. Follow these steps when using a scale (ruler):
  • Placement: Place the scale exactly along the length to be measured.
  • Starting Point: Align the starting point of the object with the Zero (0) mark of the scale.
  • Broken Zero Mark: If the zero mark is damaged or unclear, start from another full mark (like 1 cm). Then, subtract this starting mark's value from the final reading (e.g., if you start at 1 cm and end at 8.5 cm, the length is 8.5 - 1 = 7.5 cm).
  • Eye Position: Keep your eye vertically above the mark being read on the scale. Viewing from the side (left or right) can cause parallax error, leading to an incorrect reading.
• Measuring a Curved Line:
  • Using a Thread: Lay a thread carefully along the path of the curved line. Mark the start and end points on the thread. Straighten the thread and measure its length against a standard scale.
  • Using a Divider: (Less common method taught) Set the divider to a small known length. 'Walk' the divider along the curve, counting the steps. Multiply the step count by the divider length. Measure any remaining small portion separately.

4. Motion and Rest

• Rest: An object is at rest if its position does not change with respect to its immediate surroundings over time. (e.g., a book lying on a table).
• Motion: An object is in motion if its position changes continuously with respect to its immediate surroundings over time. (e.g., a running car, a flying bird).
• Relativity: Rest and motion are relative. A passenger inside a moving train is at rest relative to the train compartment but in motion relative to the trees outside.

5. Types of Motion

• Objects move in different ways. We classify motion based on the path taken:
  • Rectilinear Motion: Motion along a straight line.
    • Examples: A car on a straight highway, a bullet fired from a gun, an athlete running a 100m race, a stone falling freely from a height.
  • Circular Motion: Motion along a circular path. The distance from a fixed centre point remains constant.
    • Examples: The tip of the hands of a clock, a point on the blade of a rotating fan, a satellite orbiting the Earth, a stone whirled on a string.
  • Rotational Motion: An object spins or turns about a fixed axis that passes through the object itself.
    • Examples: A spinning top, rotation of the Earth on its axis, a rotating ceiling fan (the fan as a whole rotates), a potter's wheel. (Note: Parts of a rotating object undergo circular motion).
  • Periodic Motion: Motion that repeats itself after a fixed interval of time.
    • Examples: Motion of a pendulum, movement of a child on a swing, heartbeat, hands of a clock (also circular/rotational), revolution of the Earth around the Sun (also circular).

6. Combination of Motions

• Often, an object exhibits more than one type of motion simultaneously.
  • Example 1: A ball rolling on the ground has rectilinear motion (moves forward) and rotational motion (spins).
  • Example 2: The wheel of a moving bicycle has rotational motion (around the axle) and rectilinear motion (moves forward with the bicycle).
  • Example 3: The needle of a sewing machine moves up and down (rectilinear) and this motion repeats (periodic).
  • Example 4: The Earth undergoes rotation (on its axis - periodic) and revolution (around the Sun - circular and periodic).

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on Chapter 10 to test your understanding:

1. Which of the following represents the SI unit for measuring length?
   a) Cubit
   b) Kilogram
   c) Metre
   d) Hand span

2. Motion of the tip of a second's hand of a clock is an example of:
   a) Rectilinear motion
   b) Circular motion
   c) Rotational motion
   d) Random motion

3. To avoid parallax error while measuring length with a ruler, your eye should be positioned:
   a) Slightly to the left of the mark
   b) Vertically above the mark being read
   c) Slightly to the right of the mark
   d) At a comfortable distance, angle doesn't matter

4. How many millimetres make one metre?
   a) 10
   b) 100
   c) 1000
   d) 10000

5. A soldier marching in a parade on a straight path is executing:
   a) Periodic motion
   b) Circular motion
   c) Rotational motion
   d) Rectilinear motion

6. Which of these motions is always periodic?
   a) Motion of a bouncing ball
   b) Motion of a swing
   c) Motion of a car on a road
   d) Motion of a flying kite

7. A spinning top exhibits which type of motion?
   a) Circular motion
   b) Rectilinear motion
   c) Rotational motion
   d) Periodic motion

8. Which ancient unit of measurement is the length from the elbow to the tip of the middle finger?
   a) Footstep
   b) Hand span
   c) Angul
   d) Cubit

9. A bicycle moving on a straight road 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 NOT a standard unit of measurement?
    a) Metre
    b) Kilogram
    c) Second
    d) Footstep

Answer Key for MCQs:

1. c) Metre
2. b) Circular motion
3. b) Vertically above the mark being read
4. c) 1000
5. d) Rectilinear motion
6. b) Motion of a swing (ideally, ignoring air resistance damping)
7. c) Rotational motion
8. d) Cubit
9. c) Both rectilinear and rotational motion
10. d) Footstep

Study these notes carefully, focusing on the definitions, examples, and measurement techniques. Good luck with your preparation!