# Finding Friction Force in a 11 kg Sphere

• srhly
In summary: The person is unsure where to start but thinks they need to make a free-body diagram and label the friction force. They are given information about the magnitude of the friction force and the weight of the sphere. The question asks which of the given equations is a possible solution to the problem, and the correct answer is 4. A forum discussion is also mentioned as a resource for further learning.
srhly
I wasn't for sure where to start with this problem. It is the first of 3 so if I understand how to do this one, I will be able to most likely get the others. I'm pretty sure that I need to make a free-body diagram of the forces in this situation but wasn't for sure where to label the friction force.

A 11 kg sphere is help against a wall by a string being pulled at an angle of 62 degrees. Given: f is the magnitude of the frictional force, and W=Mg.
If the net torque is equal to zero for the center of the sphere, that leads to which of the following?
1.Fsin(angle)=f
2.F+W=f
3.Fcos^2(angle)=f
4. F=f
5.W=f

None of them look right based on what you have stated, but the statement is not clear. What is F? The force (tension) from the string? Is the angle measured relative to horizontal or vertical?

Sorry, I tried to post a picture that helped explain but it didn't work. F is the tension force of the string and the 62 degree angle is relative to the horizontal.

$$f\cdot R= F \cdot R$$

(total torque relative to the center is zero)

f - friction
F- tension in the string

clive said:

$$f\cdot R= F \cdot R$$

(total torque relative to the center is zero)

f - friction
F- tension in the string

That appears to be the only possible answer among the choices given, but it is not the only possible solution to the problem unless you know that the string is on a tangent of the sphere. So either the diagram that we have not seen shows it is tangent, or the question should be asking for a possible solution, not THE solution.

You're right OlderDan, we don't have the picture then we don't know if 1 or 4 is correct (for another ones the chances are slim to none whatever the picture would contain). So under the given circumstances 4 CAN BE an "answer". 1 can be an answer only if the angle is measured with respect to the vertical direction and the string is not tangent to the sphere.

Anyway, we're fooling around with this "without-figure" problem...

Last edited:
srhly said:
I wasn't for sure where to start with this problem. It is the first of 3 so if I understand how to do this one, I will be able to most likely get the others. I'm pretty sure that I need to make a free-body diagram of the forces in this situation but wasn't for sure where to label the friction force.

A 11 kg sphere is help against a wall by a string being pulled at an angle of 62 degrees. Given: f is the magnitude of the frictional force, and W=Mg.
If the net torque is equal to zero for the center of the sphere, that leads to which of the following?
1.Fsin(angle)=f
2.F+W=f
3.Fcos^2(angle)=f
4. F=f
5.W=f

marlon

## 1. What is friction force?

Friction force is the force that resists motion between two surfaces in contact. It is caused by the microscopic irregularities on the surfaces that interlock with each other.

## 2. How is friction force calculated?

Friction force can be calculated by multiplying the coefficient of friction (a measure of the roughness of the surfaces) by the normal force (the force pushing the surfaces together).

## 3. How do you find the coefficient of friction?

The coefficient of friction can be found by dividing the force required to move an object by the normal force acting on the object. This can be done through experiments or by consulting tables of coefficients of friction for common materials.

## 4. What factors affect friction force?

Friction force is affected by the types of materials in contact, the roughness of the surfaces, and the normal force pushing the surfaces together. It is also affected by the temperature and the presence of lubricants.

## 5. How can friction force be reduced?

Friction force can be reduced by using lubricants, polishing the surfaces, or using materials with lower coefficients of friction. It can also be reduced by decreasing the normal force or by changing the angle of the surfaces in contact.

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