Friction force without coefficient of friction?

In summary, there are two ways to calculate the friction force: by using the second formula of Newton's Second Law, or by using the coefficient of static friction. Knowing either one of these will give you the general conditions under which an object will start to slide.
  • #1
Aris Holmes
2
0
I have a problem need to be solved here. Someone told me that the friction force must always have the friction coefficient. Is it right or wrong? and we can not calculate the friction force without friction coefficient because this force is only calculated by the coefficient and the Normal force?
Is there any way to calculate friction force without coefficient because I think that there are many materials can not identify the specific coefficient?
The friction force I think is the force like Newton's Force. So can I calculate the friction force by the second fomula of Newton force: F= m x a?
 
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  • #2
Is it static or kinetic friction?
 
  • #3
I think it is static friction. But I am not sure about it. So could you mind explaining both of 2 cases
 
  • #4
Aris Holmes said:
So can I calculate the friction force by the second fomula of Newton force: F= m x a?
Yes, sure. If you know m, a, and friction is the only force acting, or you also know the other forces.
 
  • #5
The idea of a friction coefficient is just an approximation. Some surfaces don't behave this way. For example, velcro. The resistance to movement is very strong, but it doesn't scale linearly with normal force.
 
  • #6
ActionPotential's question in post #2 is very pertinent. If it is static friction, then you don't need to know the coefficient of static friction as long as the object is not yet sliding. Consider a box on an inclined plane. From a force balance in the direction along the plane, the friction force is statically determinate, and you don't need to know the coefficient of static friction. However, you do need to know the coefficient of static friction if you want to find out the conditions under which the box will start to slide.

Chet
 
  • #7
Chestermiller said:
If it is static friction, then you don't need to know the coefficient of static friction as long as the object is not yet sliding.
If it is static friction, then knowing the coefficient of static friction is almost useless to find the actual friction (except for the upper boundary). You have to know the other forces and m & a, to find the actual static friction. But if you know all this then the type of force and any coefficients are irrelevant.
 
  • #8
A.T. said:
If it is static friction, then knowing the coefficient of static friction is almost useless to find the actual friction (except for the upper boundary). You have to know the other forces and m & a, to find the actual static friction. But if you know all this then the type of force and any coefficients are irrelevant.
Yes. This is what I was trying to say in my own way. Also we should mention that, for a box on a stationary slide, ma = 0.

Chet
 

1. What is friction force without coefficient of friction?

Friction force without coefficient of friction refers to the force that opposes the motion of two surfaces in contact, without taking into account the specific materials or surface properties.

2. How is friction force without coefficient of friction calculated?

Friction force without coefficient of friction can be calculated by multiplying the normal force (the force perpendicular to the surface) by the kinetic friction coefficient. However, in this case, the coefficient of friction is not considered and the force is simply calculated as the normal force.

3. Can friction force without coefficient of friction be greater than the normal force?

Yes, friction force without coefficient of friction can be greater than the normal force. This can occur when the surfaces in contact have a high level of adhesion, resulting in a strong friction force even without a coefficient of friction.

4. What factors affect friction force without coefficient of friction?

The main factors that affect friction force without coefficient of friction are the normal force, the materials and surfaces in contact, and any external forces or motion involved. Other factors may include temperature, surface roughness, and the presence of lubricants.

5. How is friction force without coefficient of friction different from regular friction force?

The main difference between friction force without coefficient of friction and regular friction force is that the latter takes into account the specific materials and surfaces in contact, and their respective friction coefficients. Friction force without coefficient of friction is a more general concept and does not consider these factors. This can make it more difficult to accurately predict or measure the friction force without a coefficient of friction.

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