Pendulum Swing Speed Experiment
Build a pendulum and test what affects its swing speed — string length, weight, or release angle. Real physics with a real answer that surprises most people.
What You'll Need
- 1String (2-3 feet)
- 2Metal washers or small weights (3-4)
- 3Tape
- 4Table edge for hanging pendulum
- 5Timer or stopwatch
- 6Paper and pencil for data recording
What You'll Need
String (2-3 feet)
Metal washers or small weights (3-4)
Tape for securing string to a table edge
Timer or stopwatch
Paper and pencil for data recording
How to Play
Build a pendulum: tie a washer to string, tape it to the table edge.
Pull back 6 inches, release, count swings in 30 seconds.
Test weight: add more washers, same string and angle. Count swings.
Test angle: same weight and string, different release heights. Count swings.
Test string length: shorten to 1 foot, same weight and angle. Count swings.
Record all data in a table.
"Only string length changes the speed! Galileo discovered this 400 years ago."
The Science Behind It
A pendulum's period (time for one complete swing) depends only on the length of the string and gravity — not on the weight or the release angle (for small swings). This is counterintuitive: most people predict that heavier weights swing differently. Your child is learning to test one variable at a time while holding others constant — the gold standard of experimental design.
Tips
Change ONLY one variable at a time. If you change weight and string length simultaneously, you can't tell which mattered.
Count swings rather than timing one swing. Counting over 30 seconds reduces measurement error.
The surprise result (weight doesn't matter!) is what makes this experiment memorable. Don't spoil it — let your child discover it.
Ask: "Where do you see pendulums in real life?" (Grandfather clocks, swing sets, wrecking balls.)
For advanced kids: graph the relationship between string length and swing count. It's not linear — it's a square root relationship.
Frequently Asked Questions
How long does this activity take?
This activity takes about 30 min, with 5 min of preparation time beforehand.
What materials do I need?
You'll need: string (2-3 feet), metal washers or small weights (3-4), tape, table edge for hanging pendulum, timer or stopwatch, and 1 more item.
What age is this activity for?
This activity is designed for 8-12 years. You can adapt it for younger or older children by adjusting the complexity.
Can this be done indoors?
This activity is designed for indoor play, making it perfect for rainy days or when you're staying inside.
How difficult is this activity?
This activity has a moderate difficulty level. It may require some preparation or guidance, but is manageable for most families.
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