Eric Ayars made this tidy Arduino-Controlled Physics Lab Fan-Cart for simple physics demonstration. What’s a fan cart, you ask? Ah, good question! It’s basically just a fan on wheels, that can be used in physics classes to study constant force. Eric’s version goes a step further, allowing the cart to be turned on and off automatically by placing small magnets along it’s path. When the device drives over a magnet, a reed switch mounted on it’s bottom is triggered, which tells the microcontroller to start or stop. With a bit more configuration, it could also be used to vary the fan speed, allowing for more sophisticated experiments than a simple on/off switch would be allow. This could be a fun introductory project to build in a science class.