Quick Revision Notes & Formula Sheet

Class: 6th Science
Chapter: Motion and Measurement of Distances
Board: MP Board (NCERT Curriculum)

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### 1. Important Definitions (महत्वपूर्ण परिभाषाएँ)

• Measurement (मापन): The comparison of an unknown quantity with a known fixed quantity. This known fixed quantity is called a unit.
• Rest (विराम अवस्था): An object is said to be at rest if it does not change its position with respect to its surroundings with time.
• Motion (गति): An object is said to be in motion if it changes its position with respect to its surroundings with time.
• Standard Unit of Measurement (मानक मात्रक): A unit of measurement that is accepted universally across the world so that there is uniformity. (e.g., Meter).

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### 2. Historical Perspective of Measurement (मापन का इतिहास)

• Ancient Methods (प्राचीन तरीके):
  • People used body parts for measurement.
  • Cubit (हाथ की लंबाई): Length from the elbow to the finger-tips.
  • Foot (पैर): Length of a foot.
  • Hand span (बाal): Span of the hand.
• Limitation: These varied from person to person because body sizes differ. This created confusion, leading to the need for standard units.
• Introduction of Metric System (मीट्रिक प्रणाली): Introduced by the French in 1790 to create a standard set of measurements.

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### 3. SI Units (अंतर्राष्ट्रीय मात्रक प्रणाली)

• SI stands for: Système International d'Unités (International System of Units).
• Standard unit of length accepted worldwide is the Meter (m).

Standard Units Table:

Physical Quantity (भौतिक राशि)	Standard Unit (मानक मात्रक)	Symbol (प्रतीक)
Length (लंबाई)	Meter	m
Mass (द्रव्यमान)	Kilogram	kg
Time (समय)	Second	s

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### 4. Multiples and Sub-multiples of Meter (मीटर के गुणज और उप-गुणज)

To measure smaller or larger distances, we use smaller or larger units derived from the meter:

• 1 Kilometer (km) = 1000 Meters (m)
• 1 Meter (m) = 100 Centimeters (cm)
• 1 Centimeter (cm) = 10 Millimeters (mm)

Memory Trick: 1 km = 1000 m
1 m = 100 cm
1 cm = 10 mm

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### 5. Correct Way of Measuring Length (लंबाई मापने का सही तरीका)

When using a ruler or measuring tape, keep the following points in mind:

1. Placement: Place the scale in contact along the length to be measured.
2. Avoid Zero Error: In some scales, the ends may be broken. Start measuring from the 1 cm mark (or any other clear mark) and subtract that reading from the final reading.
3. Eye Position: Your eye must be exactly in front of the point where the measurement is to be taken. (Vertical view). Slanted viewing leads to errors (parallax error).

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### 6. Types of Motion (गति के प्रकार)

Objects can move in different ways. The major types of motion are:

1. Rectilinear Motion (सरल रेखीय गति):
   • Motion in a straight line.
   • Example: Marching-past of soldiers, a stone falling straight down, cars moving on a straight road.
2. Circular Motion (वृत्तीय गति):
   • Motion of an object along a circular path. The distance of the object from a fixed point remains the same.
   • Example: Motion of a point on the blade of a rotating fan, the earth revolving around the sun.
3. Rotational Motion (घूर्णन गति):
   • When an object spins about a fixed axis.
   • Example: A spinning top (लट्टू), blades of a windmill, the rotation of the Earth on its axis.
4. Periodic Motion (आवर्ती गति):
   • Motion that repeats itself after a fixed interval of time.
   • Example: Motion of a simple pendulum, the beating of a heart, hands of a clock.

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### 7. Quick Review Points (त्वरित पुनरीक्षण)

• Motion of a wheel of a bicycle is both rotational and rectilinear (translatory).
• The Earth shows rotational motion (on its axis) and circular/periodic motion (around the sun).
• Measurement needs a unit and a numerical value.