[esldummy]

My son said "Slide" is only for something (sliding) on the ground and "Glide" is only for something (gliding) in the air (like airplanes). Is this distinction correct? Thanks!

[mesmark]

On skates, you can glide across the ice.
On skates, you can slide across the ice.

I'd say your son's distinction is correct, and add that glide can also be used like slide to also mean gracefully, easily, or smoothly "slide".

[alawton]

To glide seems like a situation that is more controlled. When I am snowboarding, and I feel like I am having a good run, I feel like I am gliding down the hill. When I have a bad run, and I'm out of control, I usually am sliding down the hill out of control. I think I need more lessons....