I am trying to find out if there's a way to set up network adapters so that if 2 are connected with network and internet access it will choose one over the other.

Scenario:
I have seen several computers running Windows 7 or Windows 8 where you are connected to a wireless network, working perfectly. Then when you plug in an Ethernet cable, it still shows the network icon in the taskbar as wireless.

I would like to have my computer set up so that if there's an Ethernet cable plugged in, it uses that, and not the wireless adapter.

1) Is this possible / How?
2) Why does it stay on wireless over wired when given the option for both?