# Finding the coefficient of static friction

• dapperjon002
In summary, the conversation discusses the calculation of the coefficient of static friction needed for a car to safely travel on a banked curve with a radius of 85m at a speed of 95km/h. The equations used include centripetal force, friction force, and the relationship between tangential velocity, radius, and angle. The final calculation using the given numbers results in a coefficient of static friction of 0.81.

## Homework Statement

If a curve with a radius of 85m is properly banked for a car traveling 65 km/h what must the coefficiant of static friction be for a car not to skid when traveling at 95km/h

## Homework Equations

For this question i tried using a few equations such as centripical force, force friction where Ffric = UsFn as well as (mv^2)/R = Ffric i also though the equation Tan(theta)=V^2D/Rg was pertanent.

## The Attempt at a Solution

I set up a proportion of mv^2/R = Us(ma) and the masses canceled out so i was left with v^2/ra but i didnt really know where to go from here.

Welcome to Physics Forum, although I am quite new too.
The car is moving on a banked curve. Did you take in account the part of the normal force that points towards the centre $$N_{x}$$? Also, you should also break the friction force into components $$f_{x}$$ and $$f_{y}$$.

Ok i set up my two force components and i have Fycos(theta)=mg and Fxsin(theta)=mv^2/r when dividing both components together you are left with tan(theta)=v^2/rg and when i plug in the numbers given after converting 95 km/h to m/s you get a static friction of .81 am i doing somthing wrong because it doesn't seem right

dapperjon002 said:
Fycos(theta)=mg and Fxsin(theta)=mv^2/r

What did you mean by Fy and Fx?

1 person

## 1. What is the coefficient of static friction?

The coefficient of static friction is a value that represents the amount of force required to keep an object at rest on a surface. It is a dimensionless quantity, typically denoted by the Greek letter mu (μ), and is specific to a particular combination of two surfaces.

## 2. How is the coefficient of static friction measured?

The coefficient of static friction can be measured experimentally by gradually increasing the force applied to an object on a surface until it begins to move. The maximum force just before the object starts to move is equal to the coefficient of static friction. It can also be calculated using equations that take into account the materials and surface characteristics.

## 3. What factors affect the coefficient of static friction?

The coefficient of static friction can be affected by various factors, such as the nature of the two surfaces in contact, the roughness of the surfaces, the weight of the object, and the presence of any lubricants or contaminants on the surfaces.

## 4. Why is the coefficient of static friction important?

The coefficient of static friction is important because it helps us understand the behavior of objects at rest on surfaces. It is crucial in determining whether an object will remain stationary or start to move when a force is applied, and it is also used in engineering and design to ensure the stability and safety of structures.

## 5. Can the coefficient of static friction ever be zero?

No, the coefficient of static friction can never be zero. This would mean that there is no force required to keep an object at rest on a surface, which is not possible according to the laws of physics. However, the coefficient of static friction can be very small, especially with extremely smooth surfaces or when a lubricant is present.

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