📌 Key Concepts
✦ SI unit of length: metre (m)
✦ Conversions: 1 km = 1000 m; 1 m = 100 cm; 1 cm = 10 mm
✦ Length is measured using scale, measuring tape, metre rod
✦ Motion = change in position of an object with time
✦ Types: Linear (straight line), Circular (circle), Oscillatory (to and fro)
✦ Motion is relative — depends on the reference point
✦ Correct measurement: eye should be perpendicular to the scale (no parallax error)
Q3 Convert: (i) 5 km to m (ii) 200 cm to m (iii) 3.5 m to cm (iv) 7000 m to km
ANSWER(i) 5 km = 5 × 1000 = 5000 m
(ii) 200 cm = 200 ÷ 100 = 2 m
(iii) 3.5 m = 3.5 × 100 = 350 cm
(iv) 7000 m = 7000 ÷ 1000 = 7 km
Q5 Can an object have more than one type of motion at the same time? Give example.
ANSWERYes! An object can have more than one type of motion simultaneously.
Example: A spinning top — it rotates (circular motion) and also moves on the surface (linear). A ball rolling on the ground has both linear and circular motion. Earth rotates on its axis (circular) and revolves around the Sun (circular).
Q6 What is meant by \"motion is relative\"?
ANSWERMotion depends on the reference point (observer\'s position). A person sitting in a moving bus is at rest with respect to the bus, but in motion with respect to a tree outside. So the same object can be in motion AND at rest depending on the reference point.
Q7 Identify the type of motion: (i) Hands of a clock (ii) Pendulum of a wall clock (iii) A car on a straight road (iv) A spinning top
ANSWER(i) Hands of a clock — Circular motion
(ii) Pendulum — Oscillatory motion
(iii) Car on straight road — Linear motion
(iv) Spinning top — Circular + Linear motion