We did an activity in the chapter ‘Measurement of Length and Motion’ in the Grade 6 Science textbook Curiosity, where we observed the oscillatory motion of an eraser hung with a thread. Is the pendulum similar to that?
Answer
Yes — it is the same thing. An eraser hung from a thread and set swinging is a simple pendulum; only the name and the bob are different.
A simple pendulum. The bob hangs at the mean position O and swings between the two extreme positions A and B.
Grade 6 activity
Simple pendulum of this chapter
An eraser tied to a thread
A small metallic ball — the bob — tied to a thread
Held in the hand or hung from a hook
Hung from a rigid support
Moved to one side and released — it swings to and fro
Moved slightly to one side and released — it starts oscillatory motion
The swinging repeats again and again
The motion is periodic: it repeats its path after a fixed interval of time
Why the pendulum is treated separately: in Grade 6 we only watched the to-and-fro motion. Here we measure it. A heavy metal bob on a taut thread swings for a long time without wobbling, so the time for one oscillation — the time period — can be measured accurately. That is what makes it usable in a clock.