General Science Notes Chapter 6 Class 7 Maharashtra Board

Notes For All Chapters – General Science Class 7

Measurement of Physical Quantities

1. Introduction

• Measurement is the process of finding the size, length, mass, time, or other properties of an object.
• We measure different physical quantities like length, mass, time, temperature, and volume using standard units.

2. What is a Physical Quantity?

• A physical quantity is a property that can be measured.
• Example: Length, mass, weight, time, speed, and temperature.

Types of Physical Quantities

1. Fundamental Quantities – Cannot be broken down into simpler units.

• Example: Length, mass, time, temperature.

2. Derived Quantities – Made by combining fundamental quantities.

• Example: Speed, area, density, volume.

3. Standard Units of Measurement

• To ensure accuracy and consistency, scientists use standard units called SI units (International System of Units).

Important SI Units

4. Measurement of Length

Length is the distance between two points. Devices used for measuring length:

• Ruler/scale – Used for small objects like books.
• Measuring tape – Used for larger objects like rooms.
• Vernier calipers – Used for very small objects like wires.

Precautions while measuring length:

1. Place the ruler correctly along the object.
2. Avoid zero error (make sure the ruler starts at 0).
3. Look straight at the scale to avoid parallax error.

5. Measurement of Mass

• Mass is the amount of matter in an object.
• It is measured using a beam balance, digital balance, or spring balance.
• Mass remains constant everywhere, unlike weight.

Differences between Mass and Weight

6. Measurement of Time

• Time is measured using clocks and stopwatches.
• The most accurate clock is the atomic clock.
• SI unit of time is seconds (s).

Smaller & Larger Units of Time

• Millisecond (ms) → 1/1000 of a second
• Minute (min) → 60 seconds
• Hour (h) → 60 minutes

7. Measurement of Speed

• Speed is how fast an object moves.
• Formula: Speed = Distance/Time
• SI unit of speed: Meter per second (m/s).

Example Calculation:

• If a car travels 100 meters in 20 seconds, its speed is: 100÷20=5 m/s100 \div 20 = 5 \text{ m/s}100÷20=5 m/s

8. Measurement of Temperature

Temperature tells us how hot or cold something is.

Measured using a thermometer in units:

• Celsius (°C)
• Fahrenheit (°F)
• Kelvin (K) – SI unit

Comparison of Temperature Scales

9. Scalar and Vector Quantities

(i) Scalar Quantities

• Quantities that have only magnitude (size) but no direction.
• Example: Mass, temperature, time, speed.

(ii) Vector Quantities

• Quantities that have both magnitude and direction.
• Example: Velocity, force, weight.

10. Importance of Accurate Measurement

• Measurements are needed in daily life, science, and industries.
• Example:
  • Cooking – Correct measurement of ingredients.
  • Construction – Measuring materials accurately.
  • Science Experiments – Precise calculations for correct results.

11. Precautions While Measuring Physical Quantities

1. Always use the correct measuring instrument.
2. Avoid parallax error (wrong reading due to incorrect eye position).
3. Ensure that devices like scales and balances are properly calibrated.