Help Proove Physics Teacher Wrong

DRock9 said:

She claims then when you deflate, or inflate your tires the change in surface area does not have any effect on friction what-so-ever.

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DRock9 said:

She claimed that if you deflate your tires it will not help you get out of sand or help you on the ice, I do not know about the ice part but it helps in my friends 4x4 in the sand and on rocks I can tell ya that much.

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86bluecobra said:

Ok well it does have an effect on friction because depending oh how much your tire is inflated you can see different contact patterns with the road. For instance an over inflated tire wears out the center of the tire and not the edges. An under inflated tire wears the outer edge of tread and not the center. I would ask her to show you the formula that proves her statement. I remember my physics teacher coming up with some strange things when I was taking it. Conservation of Force??? I can't remember but it had to do with if you jump the earth has to move up to u a little?? I laughed my a$$ off. I asked if we got every human on the earth to move to one country and we all jumped at the same time could we pull the earth out of orbit? It seemed silly to me but after all they are the smartest dumb people I have met. ( actually maybe engineers are)

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Daggar said:

and this is Mustang tech how????

--drop kicked to the Talk section--

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89five.o said:

Thank an engineer everytime you sit in that car of yours

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Coefficient when surfaces not hard and sliding

In the case where a surface is soft, there is molecular adhesion, and in rolling and fluid friction, the coefficient of friction is not a simple number. The coefficient may be dependent on the area of the surfaces, the amount of deformation, the amount of adhesion, the shape of the surfaces, the radius of the wheel or the viscosity of the fluid.
What this means is that although the standard friction equation holds in these cases, the coefficient of friction will only hold for a specific configuration. In other words, you can't accurately give something like the coefficient of rolling friction for a rubber tire on pavement without stating the type of rubber, area on the pavement, inflation of the tire, and its tread pattern.

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Coefficient of rolling friction
Rolling friction is not as straightforward as sliding friction. But still, there is a relationship between the rolling friction and the normal force, similar to that in sliding friction. Often the coefficient of rolling friction is determined by assuming a form of the Standard Friction Equation holds:

FR = μR*W

where

FR is the resistive force of rolling friction,
μR is the coefficient of rolling friction for the two surfaces (Greek letter "mu" sub R), and
W is the weight of the wheel (in the case of a wheel rolling on the ground surface).
Other factors in coefficient
The coefficient of rolling friction, μR, isn't a simple number as in the case of sliding friction for hard materials. Instead, it is proportional to the width of the wheel and inversely proportional to the radius. In the case of soft wheels and tires, μR the surface area of the tire on the ground is a factor.

Determining the coefficient
A way that μR is determined is by rolling a wheel at an initial velocity, v, and then measuring the time, t, that it takes to stop.

μR = v/(t*g)

where g is the acceleration of gravity 9.8 m/s2 or 32 ft/s2.

This method and equation can be used with hard or soft wheels. Although it does not require the weight or size of the wheel to be known, it only applies for a wheel similar to that being measured.

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