Chapter 7 – Motion and Measurement of Distances

1. Introduction

  • We need to measure distances for various purposes like traveling, construction, and scientific studies.
  • Early humans measured distances using body parts like hands, feet, and arms. However, these were not standard and led to variations in measurement.

2. History of Transport

  • In ancient times, people traveled on foot or used animals like horses, camels, and elephants for transport.
  • The invention of the wheel was a revolutionary step, leading to carts, bicycles, cars, trains, and airplanes.
  • Today, we have advanced transport systems like metro trains, bullet trains, and airplanes.

3. Measurement and Standard Units

(a) What is Measurement?

  • Measurement is the process of comparing an unknown quantity with a known standard quantity.

(b) Standard Units of Measurement

  • Earlier, different regions used different units like cubit (elbow to fingertip), handspan, footstep, and fathom (length of outstretched arms).
  • The need for standardization led to the International System of Units (SI Units).
  • The SI unit of length is meter (m).
    • 1 km = 1000 m
    • 1 m = 100 cm
    • 1 cm = 10 mm

4. How to Measure Length Accurately?

  • Use a measuring tape, scale, or ruler.
  • Place the ruler along the object without tilting.
  • Read the measurement at eye level to avoid errors.
  • Start measuring from zero.

5. Motion (Types of Motion)

Motion is the change in position of an object over time. It can be of different types:

(a) Rectilinear Motion

  • An object moves in a straight line.
  • Example: A car moving on a straight road, a falling ball.

(b) Circular Motion

  • An object moves in a circular path around a fixed point.
  • Example: Hands of a clock, movement of a fan blade.

(c) Periodic Motion

  • Motion that repeats at regular intervals of time.
  • Example: Swinging of a pendulum, revolution of Earth around the Sun.

(d) Rotational Motion

  • An object rotates around its own axis.
  • Example: Rotation of Earth, spinning of a top.

(e) Mixed Motion

  • When an object shows more than one type of motion at the same time.
  • Example: A bicycle in motion has rectilinear motion (moving forward) and rotational motion (wheels rotating).

6. Important Definitions

  • Distance: The total length covered by a moving object.
  • Rest: When an object does not change its position over time.
  • Motion: When an object changes its position with respect to time.
  • Measurement: The process of determining the length, volume, mass, or any other quantity using standard units.

7. Important Questions for Exams

(a) Fill in the blanks:

  1. The SI unit of length is ____. (Ans: meter)
  2. A ball rolling on the ground shows ____ motion. (Ans: Rotational & Rectilinear)
  3. The motion of a pendulum is an example of ____ motion. (Ans: Periodic)
  4. 1 kilometer = ____ meters. (Ans: 1000 m)
  5. The rotation of the Earth is an example of ____ motion. (Ans: Rotational)

(b) True or False:

  1. The measurement of length was always the same in ancient times. (False)
  2. A fan’s blade shows rectilinear motion. (False, it is circular motion)
  3. The motion of a train on a straight track is rectilinear motion. (True)
  4. The SI unit of length is kilometer. (False, it is meter)
  5. The motion of a swing is periodic. (True)

(c) Short Answer Questions

  1. What is motion? Give two examples.
  2. Why do we need standard units of measurement?
  3. Explain circular motion with an example.
  4. What are the different types of motion?

(d) Long Answer Questions

  1. Explain different types of motion with suitable examples.
  2. Why is measurement important? How were measurements taken in ancient times?
  3. How has the development of transport changed human life?

8. Summary

  • Measurement is essential in daily life.
  • Standard units are necessary to avoid confusion.
  • Motion can be rectilinear, circular, periodic, rotational, or a combination of these.
  • The invention of the wheel revolutionized transport.
  • SI unit of length = meter (m).

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