Coefficient of Static Friction error (Lab)

In summary, to calculate the error of coefficient of static friction in a lab, one must use the general theory of errors and plug in the angle value in radians along with the uncertainty in the angle. By doing so, the final answer for the error was found to be 0.12, indicating a coefficient of static friction of 0.500 +/- .001.
  • #1
mlostrac
83
0

Homework Statement


Need to calculate the error of coefficient of static friction in a lab where: µs = tan(theta)s They say to use the general theory of errors?


Homework Equations


delta[tan(theta)] = [1/cos(theta)]^2 (delta)(theta)


The Attempt at a Solution



Do I just plug in my angle value of 26 into the theta's to get the answer? I tried that and I got a value of 0.40, which doesn't make sense because my coefficient of static friction is 0.50?
 
Physics news on Phys.org
  • #2
You are on the right track, but not there yet. Your fractional error is d(tanθ)/tanθ. To get the percent error multiply by 100. Be sure to do all calculations and express all angles in radians.
 
  • #3
kuruman said:
You are on the right track, but not there yet. Your fractional error is d(tanθ)/tanθ. To get the percent error multiply by 100. Be sure to do all calculations and express all angles in radians.

Ok so I adjusted my angle from 26.5 degrees to 0.46 rad, and then plugged that into each theta for the above equation giving me:
d(tan(theta)) = 1 x d(theta)

kinda confused on what I do after this
 
  • #4
mlostrac said:
Ok so I adjusted my angle from 26.5 degrees to 0.46 rad, and then plugged that into each theta for the above equation giving me:
d(tan(theta)) = 1 x d(theta)

kinda confused on what I do after this
I am not sure what you have done here. The fractional error in tanθ is given by the ratio

[tex]\frac{d(tan(\theta))}{tan\theta}=\frac{d \theta}{tan\theta*cos^2(\theta)}[/tex]
 
Last edited:
  • #5
kuruman said:
I am not sure what you have done here. The fractional error in tanθ is given by the ratio

[tex]\frac{d(tan(\theta))}{tan\theta}=\frac{d \theta}{tan\theta*cos^2(\theta)}[/tex]

d tan(theta)/tan(theta) = d (0.462)/ [tan(0.462) x cos (0.462)^2)]
= 0.46/0.00806
= 57.32 rad

I think my answer is way off, what am I doing wrong and why does something as simple as error calculation seem so complicated?
 
  • #6
mlostrac said:
d tan(theta)/tan(theta) = d (0.462)/ [tan(0.462) x cos (0.462)^2)]
= 0.46/0.00806
= 57.32 rad

I think my answer is way off, what am I doing wrong and why does something as simple as error calculation seem so complicated?
You seem not to understand the meaning of the symbols in the expression you are plugging in. Here θ is 0.46 radians, true enough. However, dθ is not also 0.46 rad; it represents the uncertainty in the angle. To what accuracy did you measure that angle in radians? That's your dθ. Only you, who did the experiment, can make an educated guess about the size of dθ.
 
  • #7
kuruman said:
You seem not to understand the meaning of the symbols in the expression you are plugging in. Here θ is 0.46 radians, true enough. However, dθ is not also 0.46 rad; it represents the uncertainty in the angle. To what accuracy did you measure that angle in radians? That's your dθ. Only you, who did the experiment, can make an educated guess about the size of dθ.

Oops, haha. Ok I think I got it right this time. I put my accuracy at .001, and then my answer ended up being 0.12.

So that kinda makes sense. A coefficient of static friction = 0.500 +/- .001.

Thanks for your help kuruman!
 

FAQ: Coefficient of Static Friction error (Lab)

What is the coefficient of static friction?

The coefficient of static friction is a measure of the frictional force between two surfaces in contact when one surface is stationary and the other is trying to move. It is a dimensionless quantity that represents the ratio of the maximum force required to overcome static friction to the normal force between the two surfaces.

What is the purpose of measuring the coefficient of static friction in a lab?

The purpose of measuring the coefficient of static friction in a lab is to determine the frictional properties of different materials and surfaces. This information is important for designing and engineering structures, as well as understanding how objects interact with each other in different environments.

How is the coefficient of static friction measured in a lab?

The coefficient of static friction is typically measured by using a device called a friction tester. This device applies a known force to an object and measures the force required to overcome static friction and set the object in motion. The coefficient of static friction can then be calculated using the formula μ = F/N, where μ is the coefficient of static friction, F is the applied force, and N is the normal force.

What are some common sources of error when measuring the coefficient of static friction in a lab?

Some common sources of error when measuring the coefficient of static friction in a lab include inaccurate measurements of the applied force or normal force, variations in the surface roughness or texture of the materials being tested, and external factors such as air resistance or temperature. It is important to take multiple measurements and calculate an average to minimize these errors.

How can the coefficient of static friction be used in real-world applications?

The coefficient of static friction has many practical applications in daily life, including designing tires for cars to have optimal grip on the road, determining the angle of incline for ramps and slopes to prevent slipping, and creating anti-slip materials for floors and shoes. It is also used in industries such as construction, manufacturing, and transportation to ensure the safety and efficiency of various processes and structures.

Similar threads

Back
Top