explain3D is an app, available for iOS, Android and Windows Phone, that uses 3D animations to explain how things work. It is not free (under $2 for each version) but is a great resource for educators.
Simulations (20) include:
- Car workshop – 4 stroke engine, Car clutch, Manual transmission, Disc brakes, Ignition system
 - Discover the Universe – ISS space station, Space shuttle, Solar system
 - Electricity around us – Hydroelectric dam, Wind turbine, Nuclear power plant
 - Transport simulations – Railroad switch, Submarine, Jet engine
 - Our homes – Lock and key, Elevator, Toilet, Desk Lamp
 - Tools – Jackhammer, Hand pump
 
Here is a video explaining the app:
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