Travellers to southeast Asia frequently marvel at the showman-like skill with which street vendors prepare a drink known as teh tarik (“pulled tea”). They might not realise those same vendors are intuitive physicists at heart.
Teh tarik is the national beverage of Malaysia, a mixture of black tea and condensed or evaporated milk, whipped into a froth by rapidly pouring (“pulling”) the liquid back and forth between two cups. Sure, you could technically achieve the same effect with a handheld mixer, but where’s the fun in that? As travel writer/photographer Carey Jones wrote for Serious Eats:
It’s all about theatre, of course. Though the pouring may mix and aerate, a one-foot pour is probably as effective as a two-foot. But vendors pride themselves on their tea-pulling skill, the higher the better. It’s awfully fun to watch as they whip the tea back and forth in just seconds, long trails of liquid streaming through the air, flying between vessels.
It’s also all about the physics — and not just the physics of that foamy top. These street vendors have mastered a delicate balance between dueling forces: gravity, which is pulling the tea out of the mug, and a centrifugal effect produced as the vendor spins, pushing the tea to the bottom of the mug. (The tea itself has inertia.)
The folks at The Science Channel’s Outrageous Acts of Science are eager tell you more about the underlying physics behind preparing this quintessential Malaysian beverage:
[h/t: The Kid Should See This]