Q1.
Gently hold the bob, move it slightly to one side and release it. Take care not to push the bob while releasing it and that the string is taut. Is your pendulum now oscillating?
Answer
Yes. The bob swings from one side to the other and back again, again and again, along the same path — that is oscillatory motion, and it is periodic because the path repeats after a fixed interval of time.
Two cautions in the step decide whether the experiment will work:
- Do not push the bob. A push gives it extra speed, the swing becomes wide and irregular, and the readings scatter.
- Keep the string taut. A loose string makes the bob dip and jerk instead of swinging along a smooth arc, and the length of the pendulum keeps changing.
Why it does not go on for ever: air resistance and rubbing at the support take away a little energy in every swing, so the bob rises less each time and finally stops. Notice, though, that as the swing becomes smaller the time period hardly changes — which is precisely what makes a pendulum a good timekeeper.