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A Brass Engine That Runs On A Cup Of Tea

it powers nothing

Useless Gadgets

A Brass Engine That Runs On A Cup Of Tea

A polished low-temperature Stirling engine. Set it on anything warm and the flywheel turns, driven by nothing but the temperature difference.

Buy this nonsense$43.13$21.56(sponsored link, opens in a new tab)
  • stirling engine
  • heat engine
  • desk toy
  • brass
  • physics
  • kinetic

What Is This Thing?

A low-temperature differential Stirling engine: a brass flywheel, a glass displacer cylinder and a polished base, about 15cm tall.

Put it on top of a mug of hot tea. Within a minute the flywheel begins to turn, and it keeps turning — slowly, evenly, silently — until the tea goes cold.

There is no fuel, no battery and no motor. It runs on the difference between the temperature of the mug and the temperature of the room, which is a real and complete explanation that still sounds like a trick.

Why You Don't Need It

It powers nothing. The flywheel is connected to the flywheel. You could, in principle, attach a tiny generator and light an LED, and this model does not come with one.

It is also fussy. A low-temperature engine has very little energy to work with, so it needs a flat surface, a genuine temperature gap, and no draught.

Why You'll Buy It Anyway

Because almost nothing else in a house converts heat into motion where you can watch it happen. Every engine you own is sealed inside something. This one is open, slow enough to follow with your eyes, and made of brass and glass so you can see every part doing its job.

Robert Stirling patented the cycle in 1816 as a safer alternative to steam boilers, which were killing people. Two centuries later it is a desk ornament that runs on a hot drink.

A Brass Engine That Runs On A Cup Of Tea — photograph 2
A Brass Engine That Runs On A Cup Of Tea — photograph 3

Who It's Actually For

Engineers, and people who like engineers. It is the correct gift for someone who has a workshop, or who has ever explained a thermodynamic cycle at a dinner table.

Also teachers of physics, where it does in thirty seconds what a diagram of an isothermal expansion does not.

before you click buy

Low-temperature is the important phrase and it is easy to buy the wrong thing. The engines that run on a spirit burner look similar in photographs, cost about the same, and need an open flame on your desk.

Give the flywheel a starting flick. These are not self-starting, and a review complaining that it does not work is almost always this.

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