Motion and Measurement of Distances

Class 6 Science | CBSE NCERT Curriculum

This chapter explains the story of transport, need for standard units of measurement, SI units, correct measurement of length, measuring curved lines using thread, and types of motion including rectilinear, circular, and periodic motion.

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Quick Revision: Motion and Measurement of Distances

  • Transport Evolution: Walking → Animals → Boats → Wheeled carts → Steam engine → Automobiles → Aeroplanes → Spacecraft.
  • Ancient Units: Foot, cubit (elbow to fingertip), yard (chin to outstretched arm), angul (finger), mutthi (fist).
  • SI Units (International System): Standard units accepted worldwide for uniformity.
  • Length Units: 1 kilometre (km) = 1000 metres (m); 1 metre = 100 centimetres (cm); 1 cm = 10 millimetres (mm).
  • Correct Measurement: Scale along object, eye vertically above reading point, use any full mark if zero broken.
  • Curved Line Measurement: Use thread along curve, then measure thread length on scale.
  • Motion: Change in position of an object with time.
  • Rectilinear Motion: Motion along a straight line (e.g., car on straight road, falling stone).
  • Circular Motion: Motion along a circular path; distance from centre constant (e.g., fan blades, clock hands).
  • Periodic Motion: Motion that repeats after a fixed interval of time (e.g., pendulum, swing, vibrating guitar string).
  • Combined Motion: Some objects show multiple motions (e.g., rolling ball has rectilinear + rotational).

Chapter Summary: Motion and Measurement of Distances

Transportation has evolved from walking and animal-driven carts to modern aeroplanes and spacecraft. Measurement of distances became essential for navigation and trade. Ancient units like foot, cubit, and handspan varied between individuals, causing confusion. To solve this, the International System of Units (SI) was developed, with the metre as the standard unit of length. 1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm.

Correct measurement requires placing the scale along the object, keeping the eye vertically above the reading point, and using a suitable device. Curved lines can be measured using a thread. Motion is change in position with time. Rectilinear motion is along a straight line. Circular motion keeps a fixed distance from centre. Periodic motion repeats after fixed time intervals. Many objects show combinations of these motions.