Measurement of Length and Motion – Class 6 Science notes, important questions and MCQs

Chapter overview

Measurement compares a quantity with a standard unit. Length is measured in metres, and objects can move in different ways — straight, circular or to-and-fro.

Measuring length

• Early units like handspan and cubit varied from person to person, so standard units were needed.
• SI unit of length is the metre (m); 1 m = 100 cm, 1 km = 1000 m, 1 cm = 10 mm.
• Measure correctly: start at zero, keep the eye directly above the mark, use a thread for curved lines.

Types of motion

• Linear (rectilinear): along a straight line (a falling stone).
• Circular: along a circle (a fan blade tip).
• Periodic (oscillatory): repeats after a fixed time (a pendulum, a swing).

Key terms

Standard unit

unit that is the same everywhere

Rectilinear motion

motion along a straight line

Periodic motion

motion that repeats after equal intervals of time

Formulas

• 1 km = 1000 m = 1,00,000 cm

Important questions with answers

Quick revision

• SI unit of length: metre.
• Eye must be vertically above the mark.
• Pendulum motion is periodic.

Exam tips

• If the scale's zero mark is broken, start from 1 cm and subtract 1 from the reading.
• Earth's spin is periodic; a car on a straight road is linear.

Practice MCQs

1. SI unit of length is

   1. centimetre
   2. inch
   3. kilometre
   4. metre
   Show answer

   Answer: (d) metre. Metre.

2. Motion of a fan's blade tip is

   1. circular
   2. linear
   3. zigzag
   4. random
   Show answer

   Answer: (a) circular. Circular.

3. 2.5 m equals

   1. 250 cm
   2. 25 cm
   3. 2500 cm
   4. 0.25 cm
   Show answer

   Answer: (a) 250 cm. 2.5 × 100.

4. A swing shows

   1. linear motion
   2. circular motion only
   3. no motion
   4. periodic motion
   Show answer

   Answer: (d) periodic motion. Repeats to and fro.

5. The SI unit of length is

   1. centimetre
   2. foot
   3. kilometre
   4. metre
   Show answer

   Answer: (d) metre. Metre.

6. A scale's broken end starts at 2 cm. The object ends at 9.5 cm. Its length is

   1. 9.5 cm
   2. 2 cm
   3. 11.5 cm
   4. 7.5 cm
   Show answer

   Answer: (d) 7.5 cm. 9.5 − 2.

7. Why did people need standard units?

   1. they liked numbers
   2. body measures differ from person to person
   3. to make rulers longer
   4. to avoid measuring
   Show answer

   Answer: (b) body measures differ from person to person. Uniformity.

8. The motion of a swing is

   1. periodic (oscillatory)
   2. circular
   3. rectilinear
   4. random
   Show answer

   Answer: (a) periodic (oscillatory). Repeats after a fixed time.