 Poster: A snowHead
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If Galileo proved that all objects fall at the same rate regardless of mass then can someone please explain why at a svelte 95kg I tend to travel much faster along cat tracks than lighter people?
It's not just a question of retaining my speed better from a previous slope as the effect can still be seen from a standing start. I can imagine it may be something to do with mass in relation to ski area, but then again the ski should, surely, be in proportion to weight.
Thoughts?
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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You're keeping your speed up by staying on your edges, others will be skidding their skis and scrubbing off a bit of speed.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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rob@rar, No, I genuinely don't think that is the answer as the phenomenon occurs principally/only on dead flat pistes where everyone is just trolling along in a 15mph schuss. Trust me, superior ability has NOTHING to do with it!
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foxtrotzulu, some people will be skiing on their inside edges, some people will twists their skis to make slight changes of direction, others will carve and not lose as much speed.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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Selective Gravity - I've found the same thing happens on both skis and freewheeling on my MTB. The only advantage of being overweight.
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rob@rar, OK, I'm still a little dubious but happy to accept your answer if you can explain to me why this phenomenon seems to have a strong correlation with weight. Heavier people like me do seem to go faster on some flatter slopes. Why would we be more likely to stay on our edges than others? Wouldn't staying on our edges cause us to turn?
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So nowt to do with edges etc. (althoguh that will make a difference, but heavier will win if all else is equal)
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You'll get to see more forums and be part of the best ski club on the net.
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martinm, but doesn't the conservation of energy mean that mgh up the hill becomes 0.5mv2 at the bottom, so the velocity of any skier is sqrt(mgh/0.5m) so the m's cancel and the veloicity is irrespective of weight?
I would have thought that the wax would have a significant impact.
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Big people have a higher ratio of mass to surface area than do small people, As a result, air resistance slows down the small people more.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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martinm, Two thoughts:
1. I would have thought that friction was more of a factor than air resistance.
2. Air resistance (parasitic drag) increases disproportionately fast as speed increases, and yet this is a phenomenon more pronounced at slower speeds.
If you were correct about this, wouldn't speed skiers, luge riders etc. all look like darts players?
Despite my quibbles, I suspect your on the right track.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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In true free fall the object with the larger mass has the greater inertia. I wonder when sliding horizontally whether the inertia is less relevant.
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foxtrotzulu, it gets complicated by fatty tissue being less dense than muscle.
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You know it makes sense.
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Ray Zorro, that's in a frictionless system though.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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foxtrotzulu, Not much friction on compacted snow!
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Poster: A snowHead
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We need someone to explain this properly. There must be some physicists round here. Other things being equal (skill, length of skis) IME a heavier person will glide faster down a cat track than a lighter one. As the OP said. Maybe something to do with friction? the skiers are not dropping through air, they are sliding along a surface. What happens if you roll two things (cylinders, for example) down sloping surfaces of varying friction. A smooth wooden board, a board with green baize, a board with a low pile carpet, a board with a high pile carpet. The time will come when the light one will not overcome friction, and the heavy one does. The advantage of the heavy one would prove particularly useful if they then encountered a much flatter bit of slope.
If the heavy person swaps his long skis for blades, the lighter person would probably win - more friction?
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Ignoring friction you then have a proportion of the force from gravity balancing against air resistance. The force due to gravity is proportional to mass, the force due to air resistance isn't. The result is that increasing mass will increase the air resistance force required to balance the forces and so the larger skier reaches a higher terminal speed.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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Sintered bases, better wax job.
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You need to Login to know who's really who.
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Could be completely wrong but I thought it was because the heavier person exerts more force on the snow, which compresses the snow more and reduces the friction. Gravity is proportional to the weight so the difference all other things being equal should be friction and wind resitance. The properties of H2O change considerably around freezing point/under pressure. Just like it is a lot quicker skating over ice than it is swimming through water. I thought this was one of the reaosns FIS had a weight limit on skis?
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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Would it have anything to do with the fact that skis move across snow because the pressure of the skis on the snow melts it enough to create a bit of water, allowing the skis to glide. Therefore, the heavier you are, the more pressure applied and, thus, the more melt, resulting in quicker glide?
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What is going to have more of an effect: quality of waxing, air resistance, conservation of energy, or whether a skier is in a slight but permanent snowplough when skiing on a cat track? If I want to pass people of a cat track I stay on my edges, making slight carved turns. If I want to slow down I'll put in some gentle skiddy turns, or perhaps a slight plough shape. Compared to how your skis are running on the snow other factors are insignificant.
Last edited by You'll need to Register first of course. on Tue 5-03-13 13:08; edited 1 time in total
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See:The Physics of Skiing
Section 15.2 asks 'Do big people go faster?' and concludes that they are likely to do so.
Unfortunately it says nothing on the subject of inner tip lead...
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TTT, I think you and I are on the same track!
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You'll get to see more forums and be part of the best ski club on the net.
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Zero-G, but who's going faster? 
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sloop,  Since I'm a woman of insubstantial mass, probably TTT!
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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rob@rar, absolutely but all things being equal fatties do still have the advantage.
As for which is more significant that all depends on who is overtaking who and what their relevant differences actual are.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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meh, I'm sure that there are a huge range of factors that affect our speed when we ski. However, if someone wants to go a bit faster on cat tracks which is the better advice: improve your technique or eat more pies?
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rob@rar, the accepted snowHeads response to any question is eat more pies!
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You know it makes sense.
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Zero-G,
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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rob@rar, the answer is obviously improve technique since that is probably what is wrong. That wasn't the question though, it was basically "do fatties have any advantage in this situation and why" to which the answer is a straightforward, yes because in this situation additional mass is an advantage all other things being equal. If someone then asked "but why do some skinnies go faster than me" an exploration of the factors that might not be equal including technique would make more sense.
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Poster: A snowHead
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rob@rar, the advice they want to hear is 'eat more pies'.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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| meh wrote: |
| rob@rar, the answer is obviously improve technique since that is probably what is wrong. That wasn't the question though, it was basically "do fatties have any advantage in this situation and why" |
No, he asked why he travelled faster on cat tracks, including from a standing start (when having greater momentum from a steepr slope because if a larger mass wouldn't have an effect). So I gave him an answer which I think is far more likely to explain the situation than delving into a A level physics curriculum.
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rob@rar, well you obviously read the OP in your own way which is nice but given the main difference noted was weight and the OP does some speculation of their own about how mass plays into the physics involved I do think a physics based answer is a bit closer to what they were fishing for. Also the reference to a famous physicist in the title and first sentence!
A heavier skier still has an advantage from a standing start too. This is also only GCSE Physics at best. 
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| tiffin wrote: |
http://www.math.utah.edu/~eyre/rsbfaq/physics.html
scroll down to 15.2
try and make sense of it
come back and tell me what it means |
If all other things are equal, greater pressure from the increased mass will cause increased temperature, causing the snow under the ski to melt a tiny bit more quickly.
http://www.mechanicsofsport.com/skiing/basic_mechanics/why.html
Different for mountain bikes. In order to move a tyre, you need to apply a force to overcome the rolling resistance. The rolling resistance is proportionately less as the mass increases
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meh, I understood the physics references but I don't think they are significant compared to what the skis are actually doing against the snow. So I considered the physics references to be a bit of a red herring and gave an answer which I think answered the general question far better than the direction the OP wanted to head towards. But maybe I'm wrong as my A level physics is a long way behind me, and the differences I see in technique being applied by skiers on cat tracks is, in fact, of no consequence compared to the relative size of the skiers in question...
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OK but how about a straight schuss speed trap? The bigger guys seemed to be getting a faster time which seems to support the lower fricction argument. Having said that I think I "won" because of freshly services skis and a lower more aerodynamic tuck position rather than the tightness of my ski trousers this season.
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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rob@rar, if you look above you'll find I've agreed with you several times that technique is the most important factor in the real world. The obvious comparison would be between someone skiing parallel versus someone of equal weight skiing in a snowplough. That doesn't negate the fact that a heavier skier is at an advantage should they be skiing against someone with roughly the same technical competence.
TTT, it's all a lower friction argument, differently chosen and applied techniques or poor technique increase friction either between the skis and the snow or between the skier and the air they are moving through. Trying to ski fast in particular makes air resistance a very significant factor. Terminal speed of a human in freefall is only approximately 200km/h and that's under the full force of gravity, traveling down any slope significantly lowers the proportion of the force due to gravity acting against air resistance dropping the terminal speed quite a lot as well.
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| tiffin wrote: |
| come back and tell me what it means |
The summary is in the last equatio:
A = g*sin(theta) - mu*g*cos(theta) - (Cd*Ap*rho*V^2)/(2*m)
A = acceleratio of skier
g*sin(theta) = acceleratio due to gravity
mu*g*cos(theta) = loss of acceleratio due to snow friction
(Cd*Ap*rho*V^2)/(2*m) = loss of acceleratio due to air drag
Notice that 'm' (= mass of skier) only appears in the last term - and then in the bottom line.
From this we can say that most of the acceleratio of the skier is independant of mass. However, the loss due to wind drag gets smaller with increased mass. Therefore the heavier skier will go faster - slightly.
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FAQ
