# Maximum attainable coefficient of static friction

• canza
In summary, the record was set by Shirley Muldowney in 1989 with a time of 4.96 seconds. She achieved this by having the rear wheels lift the front wheels off the ground. This minimum value of µs is necessary to achieve a time of 6.04 seconds.
canza

## Homework Statement

Hi, I'm having trouble with this question. I don't seem to get this at all. I hope you guys can help me on this.

Before 1960, it was believed that the maximum attainable coefficient of static friction for an automobile tire was less than 1. Then, about 1962, three companies independently developed racing tires with coefficients of 1.6. Since then, tires have improved, as illustrated in this problem. According to the 1990 Guinness Book of Records, the shortest time in which a piston-engine car initially at rest has covered a distance of one-quarter mile is 4.96 s. This record was set by Shirley Muldowney in September 1989.

Assume that, as in the figure, the rear wheels lifted the front wheels off the pavement. What minimum value of µs is necessary to achieve a time of 6.04 s?

Why do they speak of the front wheels lifting off the ground?

We have a distance, a time, an initial velocity; can you work out the average acceleration?

What's the average forward force?

What's the normal reaction to the car's weight?

What's the kinetic frictional force?

If we don't want the wheels to spin what condition must hold?

I hope this helps you get some traction

Carid said:
Why do they speak of the front wheels lifting off the ground?
Rear wheel drive, where all of the car's weight is supported by the normal force from the rear tires. The rotation of the vehicle is due to the eccentricity of the driving friction force (at the rear wheels) relative to the c.g of the car, creating a torque which causes the car to rotate off its front wheels and pivot about its rear wheels.

The knowledge that the front tires are lifted indicates torque which is directly related to the static friction acting on the tires. If the figure tells you the angle of lift, what missing information can you compute to determine average acceleration?

PhantomJay and Mr. Amin

My question about the wheels was rhetorical. I think it's in the question just so all the weight of the car is on the rear wheels. Nothing fancy!

Fair enough.
Let's assume that the front tires "barely" leave the ground. This implies the rear tires DO NOT slip. Now since you know that the vehicle starts from rest, (1) what does the position equation look like? (2) From a term in this equation what term says anything about...force?

Carid said:
PhantomJay and Mr. Amin

My question about the wheels was rhetorical. I think it's in the question just so all the weight of the car is on the rear wheels. Nothing fancy!
I agree!

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

The maximum attainable coefficient of static friction, also known as the coefficient of limiting friction, is the maximum amount of friction that can be generated between two surfaces in contact without causing motion between them.

## 2. How is the maximum attainable coefficient of static friction determined?

The maximum attainable coefficient of static friction is determined by conducting experiments where different surfaces are pushed against each other with increasing force until the point where motion just starts to occur. The ratio of the minimum force required to initiate motion to the perpendicular force acting between the two surfaces is the maximum attainable coefficient of static friction.

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

The maximum attainable coefficient of static friction is affected by various factors such as the roughness and nature of the surfaces in contact, the amount of force applied, and the presence of any lubricants or fluids between the surfaces. It also depends on the temperature and humidity of the environment.

## 4. How does the maximum attainable coefficient of static friction differ from the coefficient of kinetic friction?

The maximum attainable coefficient of static friction is the maximum amount of friction that can be generated between two surfaces without causing motion, while the coefficient of kinetic friction is the amount of friction between two surfaces in motion. The coefficient of kinetic friction is usually lower than the maximum attainable coefficient of static friction.

## 5. Why is the maximum attainable coefficient of static friction important?

The maximum attainable coefficient of static friction is important in understanding the behavior of objects in contact with each other. It helps engineers and scientists design and build structures and machines that can withstand different forces and prevent motion when needed. It also plays a crucial role in the study of friction and the development of new materials with optimized frictional properties.

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