Pendulum Timer
A swinging mass keeps remarkably steady time — build one and discover what really sets its rhythm.
Start building ↓The build
Hang the bob
Tie the weight to the string and suspend it so it swings freely.
Measure the length
Record the length from pivot to the centre of the bob.
Start small
Pull it back a small angle and release.
Time 10 swings
Count ten full swings and divide to find the period.
A pendulum's period depends almost entirely on its length and gravity, not on its mass or (for small swings) its amplitude.
A closer look
Restoring force from gravity pulls the bob back toward centre, producing simple harmonic motion with period T = 2π√(L/g).
Variables to test
- 1 Change the string length and re-time. Does period scale with √L?
- 2 Swap a heavier bob — does the period really stay the same?
More Physics
Homopolar Motor
A single AA battery, a magnet and a copper-wire loop spin into the simplest electric motor that actually works.
Switchable Electromagnet
Coil insulated wire around an iron bolt and a battery turns it into a magnet you can switch on, off, and strengthen at will.
Balloon Hovercraft
A balloon, a CD and a bottle cap make a puck that glides almost frictionlessly across a table.