system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't microwave ovens heat up air?

When I open a regular oven, a wave of hot air rushes out because the entire interior of the oven has been heated up. Yet, when I open a microwave oven, the only thing that's hot inside is my food. Why is this? Do microwaves only heat certain substances?
gpt
Because water molecules are polar (have positively and negatively charged ends) so the oscillating EM field affects those molecules, but molecules that comprise air (O2, N2, etc) are non-polar, so the oscillating EM field doesn't affect them.