Chapter 5: Measurement of Length and Motion
How long is your pencil? How far is your school? Is the bus moving or are you? In this chapter we learn why we need standard units, how to measure lengths correctly (even curved ones), how to describe position, and the different ways things move.
In this chapter you will
- understand why we need standard units
- measure lengths correctly with a ruler and a thread
- describe position using a reference point
- identify linear, circular and oscillatory motion
Topics
- How do we Measure? NCERT 5.1
Measuring compares a quantity with a unit; a measurement is a number plus a unit.
- Standard Units NCERT 5.2
The SI unit of length is the metre (m).
- Measuring Length Correctly, Even Curved Lines NCERT 5.3–5.4
Length = reading at the end − reading at the start. A broken ruler still works.
- Describing Position NCERT 5.5
Position is described using a reference point, distance and direction.
- Moving Things and Types of Motion NCERT 5.6–5.7
Linear: straight line. Circular: round a centre. Oscillatory: to and fro.
Key words
- Unit
- a fixed quantity used for measuring
- SI unit of length
- the metre (m)
- Reference point
- a fixed place from which position is described
- Motion
- change of position with time
- Linear, circular, oscillatory
- straight line, round a centre, to and fro
- Periodic motion
- motion that repeats after equal intervals of time
Summary
- Measuring compares a quantity with a standard unit; the SI unit of length is the metre.
- 1 km = 1000 m, 1 m = 100 cm, 1 cm = 10 mm.
- Measure correctly: ruler along the object, eye straight above, length = end − start; use a thread for curves.
- Motion is change of position with time, judged from a reference point. Types: linear, circular, oscillatory.