Stirling engine is a nice education model for students and teachers. It can help to better understand the working principle.   Features: A Stirling engine is a heat engine that operates by cyclic compression and expansion of air or other gas (the working fluid) at different temperatures, such that there is a net conversion of heat energy to mechanical work.  Teacher can make the explaining process much straightforward and students can better understand its principle.  Run freely on the top of a cup of hot water, no need to fire a alcohol lamp,safer for children.  Start temperature difference between the product bottom contact and circumstance should be greater than 25℃.  Gently flip the wheel, then it can run itself.  Exquisite frosted plunger can avoid steam leakage and the reduce abrasion.  If the friction between flywheel and support is big, please use a little graphite dry lube quiet it down nicely. Don't use oil, because it will lead to oil-dirt.   Specifications: Wheel Color: Gold / Purple (Optional);  Material: Stainless steel+spray paint carbon steel+glass;  Principle of Operation: Heating expansion / cold compression;  Speed: 180rpm (max.);  Item Size: 12.2 * 10.2 * 10.2cm / 4.8 * 4 * 4in;  Item Weight: 250g / 8.8oz;  Package Weight: 333g / 11.7oz;  Package Size: 17.3 * 9.5 * 11cm / 6.8 * 3.7 * 4.3in;   Package List: 1 * Low Temperature Stirling Engine Model DIY Kit;  1 * User Manual Manual;   Note: Children under 12-year-old should be accompanied by adult when playing this product.