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 Post subject: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 3:26 am 
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Why don't skiers spend more time in the air? It seems there would be less friction to slow them down.

Is it because snow/ski friction is so negligible that the extra distance of the air arc actually takes more time than a straight line on the snow?

BTW, I know skiers must contact snow to control things. I know that on Olympic downhill courses there's limited opportunity to get air. The question is about the physics of it all.


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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 3:37 am 
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First, there is the question of how they would manage to spend more time in the air. Would basically require having wings of some sort.

On the other hand, you actually don't want to spend any time in the air at all, if your friction against the snow is not too bad. The reason is because in order to move fast, you need to convert your potential energy (being high up) into kinetic energy (moving fast) as quickly as possible. To the extent that you artificially hold yourself at higher altitude, you'll be moving slower.

The ideal case would be do have skis with air bearings (like an air hockey puck). You'd hover just a few inches off the surface of the snow, so that you're almost as low as being on the snow, but have greatly reduced friction.

This really would work fabulously. And definitely would not be allowed.

I guess one factor that would not be in favor of floating on an air bearing would be that you would lose all ability to steer yourself by exerting forces on the skis. So you would want to have a straight shot down the hill, with no turns. Not a very interesting race.

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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 4:54 am 
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Tom Albrecht wrote:
I guess one factor that would not be in favor of floating on an air bearing would be that you would lose all ability to steer yourself by exerting forces on the skis. So you would want to have a straight shot down the hill, with no turns. Not a very interesting race.



Until you try to stop.


Brett


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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 5:04 am 
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If you just look at the vertical drop, the fastest way down is if you are in free-fall. The fact that you are coming down a slope dictates that you are going to stay in contact with the ground the entire run---assuming the slope is a perfectly straight ramp.
Now, add some bumps: each bump--if the dimensions are right--will get you in the air temporarily. It is, however, a "zero-sum-game"---meaning that the energy saved while in the air is offset by the energy to get you into the air, and the energy associated with landing.

What makes analysis just about impossible is that the various frictional forces, including wind resistance and sliding on the snow, have some amount of non-linearity. Wind resistance, e.g. , goes as the square of the velocity.

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Last edited by pixellany on Feb Fri 16, 2018 5:34 am, edited 1 time in total.

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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 5:28 am 
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Yeah, the champs do get airborne. Just watch some of the downhill racing.
Of course, the ultimate is ski jumping. Airborne for ever and then you land.

Slalom, and to some extent, Moguls, they stay firmly on the snow in the turns, but the skis come off the snow between each turn. So again, airborne part of the race.
Watch Biathalon, which is cross-country with target shooting. The skis are up and down on the uphill, then they go into a tuck and rest a bit on the downhill, got to get the heart rate steady for target shooting. Those guys really exert themselves in the dash to the finish line.

Curling is the sport that I enjoy watching the most. Strategy and control. Of course Canada has gold medalists again this year.

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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 6:02 am 
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In the air you can't steer! Downhill skiing does not allow wings!
Cheers,
Roger

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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 1:30 pm 
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My question is what age do these skiers have to get their knees replaced?

I was watching it on the Olympics and I think I wouldn't be able to walk for a week afterward.

Noah


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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 4:25 pm 
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My opinion only. I am not a physicist.
Everything physical has trade-offs and a skier's nemesis while airborne is the drag coefficient.
Drag coefficient is a very complicated series if many formulas full of Greek letters which I
cannot begin to understand. But the long-and-short of it all is that the drag coefficient is determined
by size, parasitic drag (resistance to air flow) and lift. When a skier becomes airborne he is unable to maintain the same low profile that he can when on the ground so his body creates more drag. His body and the surface area of his skies become more exposed to the relative wind. Any time you increase lift of any airborne object, drag is increased too; you can't have one without the other. So now his body and skies are creating more lift or "flying" and drag will then increase. When the coefficient of drag becomes great enough, it overcomes lift and gravity takes over. Also bear in mind that when we're talking about snow skiing we're talking about colder temperatures and this too contributes to increased drag because cold air is more dense than warmer air and therefore the effects of any lift are increased and an increase in drag must follow.
One last component is the angle at which the skiier is "flying." When the relative wind is constant and perpendicular to the skier (such as on a straight run back on the Earth) it likely creates less drag than the dynamic changes in parasitic and induced drag as the skier faces diagonal relative wind in "flight" as gravity pulls him back to earth.
My apology for using the terms "flight" and "flying" carelessly to illustrate the condition of the skier.
Although there is probably a slight and transient component of lift ("flight") generated by the skier and his skies, he is more of a projectile such as a missile whereby his forward motion is maintained primarily by thrust.


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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 5:16 pm 
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Skiiers don't spend more time in the air because;

1 They don't have wings
2 Gravity
3 The cliff they skied off the edge of isn't very high
4 It's not the falling but the landing at the end that will kill you..............

Lol the physics of it.


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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 7:00 pm 
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They would have to get in the air to start with. Also they keep their skis / snowboards smooth and waxed on the bottom so the friction isn't much of an issue.

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 Post subject: Re: Downhill Skiing Physics Question
PostPosted: Feb Fri 16, 2018 9:38 pm 
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You know, there already exists an event where the skiers spend the majority of the time in the air.
One of my favorites to watch: Ski Jump. They catch air for 100+ meters.

If you can get the time for a 100 meter segment of the downhill ski event, you could compare Ski Jump.


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