floating pins in arduino
It's a normal behaviour. When you don't have anything connected to the pin impedance of it is really high. It basically starts to behave like an antenna an picks up everything from the surroundings. To make it stop floating you should connect something you want to measure, or a really high value resistor to ground (hundreds of kOhms even) to increase the impedance. Keep in mind however that it will behave like a divider when you connect something.