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# Physics on snow?

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Hi! I''m working on a simple skiing (slalom) game. I was doing just fine, until I stumbled upon thing called physics. I can''t find a realistic formula for acceleration on snow. Known variables are: - current angle of slope - direction of skis (angle offset) - weight of skier - current velocity Keep in mind that skier moves in X and Y direction so acceleration should probably be calculated seperately for both directions. Or am I wrong? Because during skiing weight is being transfered from one ski to the other, it would also probably be smart to calculate forces for skis separetly. Or am I wrong again? Can someone help me out, please. I don''t have much expirience in this field, so any kind of tip or trick will be very welcome.

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coefficient of friction

~don

"They that can give up essential liberty to obtain temporary safety deserve neither liberty nor safety."
- Benjamin Franklin

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I guess it would be smart to calculate the each movement seperatly... But keep the mass to the "skier" and not the skies (or whatever, I''m sure you get the point).
Actually as he''s using skies, I don''t think the friction does matter that much...

that''s what I think...

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Everything has a coefficient of friction. As he would be using skis on snow slopes, it will be different from the friction of a car on dry concrete.

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quote:
Original post by E-we
I guess it would be smart to calculate the each movement seperatly... But keep the mass to the "skier" and not the skies (or whatever, I''m sure you get the point).
Actually as he''s using skies, I don''t think the friction does matter that much...

that''s what I think...

Friction matters, otherwise a skier wouldn''t be able to turn (the edge of the skis bite into the snow when tilted, the weight of the skier curves them which is why they turn : you slide along that curve). Think ''ice patch''.

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So, if friction is what he needs, then maybe a little bit more is needed to define snow.

(Ive never gone skiing before, so I am just thinking here )
For example, i would see there being 2 types of snow, PACKED and POWDER (kiss, keep it simple).

PACKED
- friction coef would be less, so that the skiier moves faster down the hill(correct?)
- need low coef(?)

POWDER
- friction coef would be slightly higher for powder since you sink into the snow more and have more control, etc.
- need a higher coef(?)

You could then define a map which describes areas with a TYPE of snow above. Then use time of day, weather, your personal settings to change the map and presto..you got some cool skiing going on!

Of course, no one reads my replies so just do whatever you do...

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The acceleration a along a mountainside inclined at angle x > 0 to the horizontal with a coefficient of friction u is given by:

a = g(sinx - ucosx)

where g is the acceleration due to gravity (9.81 metres per sec)

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quote:
Original post by E-we
Actually as he''s using skies, I don''t think the friction does matter that much...

Hehehe, it there was no friction between ski''s & snow, you''d go 200mph+ down the mountain Like jumping out of a plane - which bring up _wind resistance_ as something to keep in mind.
Which depends on surface area and velocity.

Coef. fric''s needs to be a float anyway, may as well let it vary gradually over the snow/mountain mesh.

quote:

Of course, no one reads my replies so just do whatever you do...

KISS -> Keep It Simple Stupid

quote:

...it will be different from the friction of a car on dry concrete.

xsp when you consider that cars roll and don''t slide (generally speaking)

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a good start for your coefficient of friction would be 0.05, and then you could "tweak" it depending on if the game has the "feel" you like (i got this figure from an experiment about friction in physics class back in the day; yes i still have my old papers).
of course, this is for a specific pair of skis going straight across snow at a specific temperature (-5 celsius). but still, it is a place to start.
also, here are two websites that go into the physics of skiing much more than i care to read or re-type here for you:
http://www.math.utah.edu/~eyre/rsbfaq/physics.html
http://www.kent.wednet.edu/staff/trobinso/physicspages/PhysOf1998A/Skiing-Jacobson/physics1.html

--- krez (krezisback@aol.com)

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