The swinging bob
A pendulum repeats its path again and again.
A lamp that swings
Long ago, Galileo watched a lamp hanging from a church ceiling swing to and fro. It kept repeating the same swing.
If you pull a bob on a thread to one side and let go, what will it do?
What this lesson covers
The idea
A simple pendulum is a metal bob hung from a rigid support by a long thread; displaced from its mean position and released, it oscillates, and its motion is periodic as it repeats its path after a fixed interval.
A lamp that swings
Long ago, Galileo watched a lamp hanging from a church ceiling swing to and fro. It kept repeating the same swing.
If you pull a bob on a thread to one side and let go, what will it do?
- Swing to and fro along the same path
- Fall straight down and stop
- Fly away
Pull and release
Pull the bob to one side with the slider. Then press Release. Watch three swings.
Same path, same gap
The bob went to and fro along the same path, again and again, after a fixed interval of time. This repeating is called periodic motion.
A simple pendulum is a small metal bob hung from a rigid support by a long thread. When the bob is moved to one side and released, it oscillates, and its motion is periodic because it repeats its path after a fixed interval of time.
Notes
A simple pendulum is a metal bob hung from a rigid support by a long thread. Moved to one side and released, it oscillates. Its motion is periodic because it repeats its path after a fixed interval of time.
Check yourself
A simple pendulum is a metal bob hung from a rigid support by …
When the bob of a pendulum is pulled to one side and released, it …
Why do we say the motion of a pendulum is periodic?
The place where the bob hangs when it is at rest is called its …
- a long thread — correct. Yes!
- a short stick that cannot bend. A pendulum hangs from a long thread so that it can swing.
- a wide rubber sheet. A simple pendulum uses a thread.
- stays where it is. The bob does not stay. It oscillates.
- oscillates — correct. Yes!
- falls off the thread. The bob stays on the thread and swings to and fro.
- It goes in only one direction. A pendulum goes to and fro. Periodic means it repeats its path after a fixed interval.
- It never moves. The pendulum moves. It repeats its path again and again.
- It repeats its path after a fixed interval of time — correct. Yes!
- mean position — correct. Yes!
- extreme position. The extreme positions are the two ends of its swing.
- support. The support is what the thread is tied to.