quick question: how does air friction work?/why do things float

**holezch** · Nov8-09, 11:38 AM

is it just the reaction force of some object pushing down on the air? then how do things float? does the air friction over take the object? if so, then that means it isn't the reaction force then.. could someone clear this up for me? thank you

**Fightfish** · Nov8-09, 12:02 PM

Nope, 'air friction' or drag only exists if the object is moving relative to the medium, and thus this doesn't explain why things float (let's say an object is moving downwards, the drag force will only slow it down, but not cause it to move upwards).
They float due to upthrust ie net upwards force due to pressure differences acting on the different surfaces of the object. If the upthrust on the object is greater than or equal to the weight of the object, then it floats.

**holezch** · Nov8-09, 12:12 PM

Originally Posted by Fightfish

Nope, 'air friction' or drag only exists if the object is moving relative to the medium, and thus this doesn't explain why things float (let's say an object is moving downwards, the drag force will only slow it down, but not cause it to move upwards).
They float due to upthrust ie net upwards force due to pressure differences acting on the different surfaces of the object. If the upthrust on the object is greater than or equal to the weight of the object, then it floats.

ah, I see. thank you for your time :)