Yes, as we all know(most of us at least) an object being pulled by a force doesn''t start moving until the force exceeds the frictional force of the object... Fstatic = mass * staticconst Where staticconst is the frictionconstant of the current surfaces. When the object begins to slide, the friction decreases... My question is, how much? Is it the same for all materials? Like this: Fslide = Fstatic * slideconst = mass * staticconst * slideconst Where slideconst is a value between 0 - 1, (hopefully not) depending of the type of materials used...

No it''s not the same for all materials. There are always 2 constants given, one if the object doesnt move, and one if it''s sliding.

btw you shouldn''t use mass in your calculations but the component of the gravity force that is orthogonal to the surface the object is moving on.

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Original post by Philipp2k2
No it''s not the same for all materials. There are always 2 constants given, one if the object doesnt move, and one if it''s sliding.

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OK, two constants...

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btw you shouldn''t use mass in your calculations but the component of the gravity force that is orthogonal to the surface the object is moving on.

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Hmm... Yes, I have to take into account the normal force etc...
And use my home-made equation for calcing the length of two added vector if you know the angle between them

Hm.. I''ll see if I can find a big list ''o frictionconst''s
...
What is this? Google can''t handle enough criteria, and altavista ends up with this:
http://www.berro.com/text5.htm

I concur. It''s based on the normal ("perpendicular" and "orthogonal" mean normal) force between the two objects. So, if something is pushing a block into a table, then it''s harder to move. By contrast, a force trying to lift the block, but not strong enough to lift it completely, makes it easier to slide.

This page has some example coefficients. Really, you have to derive this experimentally; it depends on the surface smoothness of the objects, which is microscopic in nature and can''t really be represented theoretically.:

http://www.sciencejoywagon.com/physicszone/lesson/02forces/friction/friction.htm

Niiice...
Thx

Now at least I have some coeffs to work with
I''ll see if I''ll find more in time

Just a quick Q:
The length of the normal angle is allways = the length of the weight vector, right?

say, a brick on a 45° surrface, the angle between the normal and the weight is 135°, right?

I''m a little bit confused by what you wrote, but I know what you''re asking.


If you have an object on an inclined plane making an angle A with the horizontal XY plane (I''m saying Z is the height coordinate here), then the NormalForce = Weight * sin(A).

If you need it, I can draw a picture explaining this.

Here''s a quick way to determine the static friction coefficient between two objects.

Take a book and a coin... Put the book flat on a surface and the coin on top of it at one end. Slowly raise that end until the coin just starts to slide. Measure the angle between the book and the table. Do this lots of times and average the angle measurements. Take the tan of the angle. That is the static friction coefficient between the coin and the book. This works for any two objects... the tan of the angle gives the ratio of the normal and orthogonal forces acting on an object when it just starts to slide. This ratio is the friction coefficient. The experiment uses gravity to provide a constant force.

Have fun,

Timkin

this is an intereseting topic...

i have a question: i currently use collision detection in my 3D world and also use gravity on the y Axis(height). the only problem i have is , that if there is an inclined plane of say, 75 degrees, i can still move it up, that is, the gravity seems not to work here. i should only be able to move up a little bit and then pulled down by the gravity (like this is in commercial games like unreal, quake etc.).

how can i realize this behaviour?

thanks
Gammastrahler

You need to divide gravity force into to parts. One part is the normal force, the other is the ''rest'', that''s the force parallel to the surface. This is the force that pulls the player down. If it exceeds the static friction the player will start moving downwards.