Long Pendulum
Lesson notes
Overview
A long pendulum swings slowly — Foucault’s pendulum used 67 m. This topic is rated beginner and is number 127 of 227 in Physics. Core ideas and first intuitions. No prior knowledge needed.
What you are seeing
The panel above shows an interactive animation of the idea. Every slider changes one quantity so you can see its effect on the outcome. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
A long pendulum swings slowly, with period T ∝ √L. Foucault’s famous pendulum in Paris in 1851 used a 67 m wire, so each swing took about 16 seconds, and the swing plane slowly rotated, showing that the Earth rotates beneath it. The long length and heavy bob made the pendulum swing for hours. At the poles the plane would turn once per day.
Reading the relationship
The expression "T ∝ √L" is a compact summary of the idea. It uses the symbols T, L; name what each one stands for before you start. Notice that it contains a square root, so the result grows more slowly than the quantity inside it, and a proportionality, so the two sides rise and fall together. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Start by only moving one slider at a time. Say aloud what you expect, then check.
Common pitfalls
Check units and directions first. Many mistakes come from mixing up a scalar with a vector, or from using a formula outside the conditions where it holds.
How it connects
It builds on “Short Pendulum”, the topic before it in Physics. Once you are comfortable, continue with “Low Orbit”.
Why it matters
Physics explains how the world moves, heats, shines and interacts, and the same principles power technology around you.
Where you might use it
- Revising “Long Pendulum” before a class, exam or certification
- Designing vehicles, bridges and devices where motion, forces or waves must be predicted
- Understanding how sensors, lasers and communication links actually work
- Explaining everyday phenomena such as sound, light, heat and orbits
Frequently asked questions
What is Long Pendulum?
A long pendulum swings slowly — Foucault’s pendulum used 67 m. It is a beginner topic in Physics.
How do I use the Long Pendulum simulation?
The panel at the top shows an interactive animation of the idea. Every slider changes one quantity so you can see its effect on the outcome. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression T ∝ √L packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Core ideas and first intuitions. No prior knowledge needed. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “Short Pendulum”, the previous topic in Physics. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.