# Determine static coefficient of friction

• werson tan
In summary, the problem statement is incorrect as it refers to friction between blocks instead of between the blocks and the inclined surface. The solution provided is also incorrect as it uses the stated coefficients of friction in a way that disagrees with the given diagram. It is best to move on to the next problem and study the formulas for static and kinetic friction to understand when to apply each.
werson tan

## Homework Statement

why the µ for block is 0.3(between B and A) ? why can't be µ= 0.4( between B and C) ??

## The Attempt at a Solution

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The problem statement is worded incorrectly. It apparently means to consider friction between blocks and the inclined surface, not between blocks. Move on to the next problem, and study the formulas for static and kinetic friction, and when each applies.

PhanthomJay said:
The problem statement is worded incorrectly. It apparently means to consider friction between blocks and the inclined surface, not between blocks. Move on to the next problem, and study the formulas for static and kinetic friction, and when each applies.
Can you explain further ??

werson tan said:
Can you explain further ??
The first difficulty is that there is no actual question. It describes a set-up, but doesn't say what is to be determined.

Following the calculation, we see that the first step shows that block C is not about to slide down, nor does it require any support from block B. So the conclusion is that there is no force between those two blocks. However, the calculation makes use of a coefficient of static friction between block C and the ramp, whereas the description gave this as the coefficient between blocks B and C.

Next, we perform the same calculation for block B. This time we find that it will slide, if not held in place by block A. Again, it uses the stated coefficients between A and B as though they are between B and the ramp.

The calculation for block A completely ignores the force that would be exerted by block B, so disagrees with the diagram. Again, it uses the stated coefficients between A and B as though they are between A and the ramp.

In short, the question and solution are nonsense from start to finish.

azizlwl
haruspex said:
The first difficulty is that there is no actual question. It describes a set-up, but doesn't say what is to be determined.

Following the calculation, we see that the first step shows that block C is not about to slide down, nor does it require any support from block B. So the conclusion is that there is no force between those two blocks. However, the calculation makes use of a coefficient of static friction between block C and the ramp, whereas the description gave this as the coefficient between blocks B and C.

Next, we perform the same calculation for block B. This time we find that it will slide, if not held in place by block A. Again, it uses the stated coefficients between A and B as though they are between B and the ramp.

The calculation for block A completely ignores the force that would be exerted by block B, so disagrees with the diagram. Again, it uses the stated coefficients between A and B as though they are between A and the ramp.

In short, the question and solution are nonsense from start to finish.
well , i still don't understand why 0.3 is used for B , why not 0.4 is used for block B ?

werson tan said:
well , i still don't understand why 0.3 is used for B , why not 0.4 is used for block B ?
if you take the question statement as correct, there is no reason for using either. There simply is no information on the coefficients of friction between the blocks and the ramp.
If you accept that the question statement is garbled, the only way we can deduce what it should have said is by looking at the solution; what it actually said becomes irrelevant.

haruspex said:
if you take the question statement as correct, there is no reason for using either. There simply is no information on the coefficients of friction between the blocks and the ramp.
If you accept that the question statement is garbled, the only way we can deduce what it should have said is by looking at the solution; what it actually said becomes irrelevant.

PhanthomJay said:
The problem statement is worded incorrectly. It apparently means to consider friction between blocks and the inclined surface, not between blocks. Move on to the next problem, and study the formulas for static and kinetic friction, and when each applies.
why the µ for block is 0.3(between B and A) ? why can't be µ= 0.4( between B and C) ??
can you explain on that ?

Stop trying to make sense out of a problem that makes no sense, and move on.

PhanthomJay said:
Stop trying to make sense out of a problem that makes no sense, and move on.
i still didnt get you . can you explain further ?

werson tan said:
i still didnt get you . can you explain further ?
I see no way to make it any clearer than in my post #6.

haruspex said:
I see no way to make it any clearer than in my post #6.
tat means there is something wrong with the question ?

werson tan said:
tat means there is something wrong with the question ?
Yes!

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

The static coefficient of friction is a measure of the force required to initiate movement between two surfaces in contact. It is represented by the symbol μs and is a dimensionless quantity.

## 2. How is the static coefficient of friction different from kinetic coefficient of friction?

The static coefficient of friction applies to the initial resistance to motion between two surfaces, whereas the kinetic coefficient of friction applies to the resistance to motion once the surfaces are already in motion.

## 3. How is the static coefficient of friction determined?

The static coefficient of friction can be determined by conducting an experiment in which one surface is gradually pulled or pushed against another surface until movement is initiated. The force required to cause movement is divided by the weight of the object to calculate the coefficient of friction.

## 4. What factors can affect the static coefficient of friction?

The static coefficient of friction can be affected by factors such as the roughness of the surfaces, the weight of the object, and the composition of the surfaces (e.g. materials, lubrication). It can also vary depending on the direction and angle of the force applied.

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

The static coefficient of friction is important in understanding the stability and movement of objects on different surfaces. It is useful in engineering and design to ensure the safety and effectiveness of structures and mechanisms. It also has practical applications in everyday situations, such as choosing the right shoes for different types of terrain.

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