# B Air friction and speed & temperature

1. Oct 20, 2016

### victorhugo

1. It makes sense that air drag increases with speed, but is it a direct increase or to the square of the velocity? (so the faster you go the more energy wasted?)

2. What is the relationship between air temperature, pressure, and air drag? I can see how on a warmer day the molecules are further apart but moving much quicker. Thus less air drag.

3. I asked my professor about some of this last night but he had a bit too many drinks because of our graduation, so he didn't make much sense.
However, he explained something interesting about how molecules repel each other (when they come in 'contact'). He explained that if you come closer to the molecule at a low speed, it will be repelled without you losing too much energy. But if you were moving very quick, you'd get much closer to the air molecules and they'd bounce off with a greater speed, hence you'd be experiencing a higher energy loss than you would at lower speeds (because of air drag)
Something similar to that I guess.

2. Oct 21, 2016

### Simon Bridge

Drag models can be quite complicated - but they usually boil down to a drag force being proportional to the square of the speed acting opposite the direction of the velocity.

Higher pressure means more drag - basically, drag comes from an object having to drag a volume of air behind it rather than from skin friction with air molecules.
NASA has some good pages on this.

Is there a question there?

3. Oct 21, 2016

### victorhugo

Yeah, sorry. I forgot to ask how much of that is correct and an elaboration.

4. Oct 21, 2016

It's both, actually, and the two can be related.

5. Nov 8, 2016

### Stephen Tashi

Maybe there are some bad pages too. From the page http://www.space.com/15353-meteor-showers-facts-shooting-stars-skywatching-sdcmp.html
But we read elsewhere ( http://www.slate.com/blogs/bad_astr...l_meteor_leaves_a_bright_trail_behind_it.html ) that it isn't "skin friction" that is the main cause for heating meteoroids.

Edit: Also the NASA page: http://solarsystem.nasa.gov/planets/meteors/#! says:

Last edited: Nov 8, 2016
6. Nov 8, 2016

7. Nov 9, 2016