AI Summary
5 min readIn a custom-machined Delrin kendama built by Adam Savage, the ball is heavier, the string attaches at the exact center, and the whole thing is designed to spin. Michael Stevens hands it to Hannah Fry and explains the physics hack: gyroscopic stability should keep the hole facing down, making the spike catch nearly automatic. It still takes them dozens of tries. That tension—between clever design and the stubborn reality of human coordination—is the quiet spine of this episode.
The Physics Hack That Almost Works
The standard kendama has a problem: the string is attached to the ball at a random point, not the center. When you lift it, the off-center pull applies a torque, twisting the ball so the hole drifts away from the spike. You have to learn the "personality" of each individual toy. Stevens wanted to eliminate that variability. So he asked Adam Savage to build a version where the string is anchored at the precise center of the ball. "When you lift it, you don't put a torque on the ball," Stevens says. "It comes straight up with that hole facing the ground and it doesn't get twisted as much."
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What you'll learn
- 1 (00:00) **Introducing the Kendama** - Michael presents Hannah with a traditional Japanese skill toy, explaining its basic parts (the ken stick and dama ball) and how it's a more complex version of a cup-and-ball game.
- 2 (01:51) **Ad Break** - Cancer Research UK sponsorship segment.
- 3 (02:49) **Ad Break** - Trimphya (Crohn's/colitis) and Zepbound (weight management) advertisements.
- 4 (05:26) **Hannah's First Attempts** - Michael coaches Hannah on the basic "spike" catch, but she repeatedly fails to land the ball's hole on the spike.
- 5 (07:47) **Adam Savage's Physics-Hacked Kendama** - Michael reveals a custom, machined Delrin kendama built by Adam Savage, designed to use physics principles to make the trick easier.
- 6 (10:00) **Testing the Custom Kendama** - Both hosts try Adam Savage's creation, finding the gyroscopic effect makes the ball more stable and easier to catch, though still challenging.
- 7 (11:53) **The Build Process** - Michael describes the hour-long video on Adam Savage's Tested channel where they designed and machined the Delrin kendama.
+ Full timestamped outline available in the app
Guests on this episode
Show Notes
Michael hands Hannah a kendama, the Japanese cup-and-ball toy, and asks her to land a single catch. Then he brings out one built for him by Adam Savage of MythBusters and explains why a heavier kendama is a completely different physics problem.
A kendama looks like a children's toy. It is really a pendulum, a lesson in angular momentum and a catching problem borrowed from spacecraft docking. Michael and Hannah get into why the swing timing barely changes when the ball gets heavier, why the trick is to match the ball's velocity rather than grab at it, why bending your knees on the catch is doing real work, and why the paint finish on a kendama changes how it plays.
Then Hannah and Michael take on your questions: what would actually happen if you flew into Jupiter and kept going, whether there is a mathematical way to swim faster, and which books they'd hand an adult who wants to get back into maths after school ruined it.
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