Finding the Kinetic Friction Force using Mass and Acceleration

In summary, the conversation discusses finding the coefficient of kinetic friction between a steel block and an unknown type of aluminum surface. Using the mass and acceleration of the block, the frictional force and coefficient of kinetic friction can be calculated. The calculated coefficient of kinetic friction is .30, but it is uncertain if this matches the known value for the specific types of metals being used. The lab also deals with error estimates and error propagation analysis.
  • #1
Strobot
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Homework Statement


While sliding, the only force acting on the block in the horizontal direction is that of friction. From the mass of the block and its acceleration, you can find the frictional force and finally, the coefficient of kinetic friction.

Okay, so we are sliding a steel block with various added weights on a flat, clean, aluminum surface. Using a motion detector and a logging program we have come to the conclusion that the acceleration(m/s2) was:
327.6g - 2.853m/s2
577.6g - 2.8465m/s2
827.6g - 3.483m/s2
1077.6g - 2.944 m/s2
1326.6g - 2.95 m/s2

We need to find the Kinetic Friction Force using the mass and acceleration and then use the value found to help us find the coefficient of kinetic friction.

Homework Equations


Normally, the coefficient of kinetic friction can be found by taking µk*Fn

Convert grams to kg by moving the decimal place 3 places to the left.

Finally, to find the weight of an object in Newtons you multiply the mass (in kg), by the acceleration due to gravity (9.8m/s2)

The Attempt at a Solution


I first converted the 327.6g into kg, .3276kg, and multiplied it by 2.853m/s2. The answer for this was .9346N. I then plugged that value for the Kinetic Friction Force into the equation of
Fkf = µkFn. I divided .9346N by 3.21(the weight in N of the block) to get .2912.

I have done this for every value and I get .30 for the coefficient of kinetic friction every time. The problem is, I don't know how to check what the actual coefficient between aluminum and steel is (I'm not sure what kind of Aluminum it is, I saw online that Anodized Aluminum + Steel is .30). This is a percent error lab so we could just be getting different answers due to human error.
 
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  • #2
Strobot said:

Homework Statement


While sliding, the only force acting on the block in the horizontal direction is that of friction. From the mass of the block and its acceleration, you can find the frictional force and finally, the coefficient of kinetic friction.

Okay, so we are sliding a steel block with various added weights on a flat, clean, aluminum surface. Using a motion detector and a logging program we have come to the conclusion that the acceleration(m/s2) was:
327.6g - 2.853m/s2
577.6g - 2.8465m/s2
827.6g - 3.483m/s2
1077.6g - 2.944 m/s2
1326.6g - 2.95 m/s2

We need to find the Kinetic Friction Force using the mass and acceleration and then use the value found to help us find the coefficient of kinetic friction.


Homework Equations


Normally, the coefficient of kinetic friction can be found by taking µk*Fn

Convert grams to kg by moving the decimal place 3 places to the left.

Finally, to find the weight of an object in Newtons you multiply the mass (in kg), by the acceleration due to gravity (9.8m/s2)

The Attempt at a Solution


I first converted the 327.6g into kg, .3276kg, and multiplied it by 2.853m/s2. The answer for this was .9346N. I then plugged that value for the Kinetic Friction Force into the equation of
Fkf = µkFn. I divided .9346N by 3.21(the weight in N of the block) to get .2912.

I have done this for every value and I get .30 for the coefficient of kinetic friction every time. The problem is, I don't know how to check what the actual coefficient between aluminum and steel is (I'm not sure what kind of Aluminum it is, I saw online that Anodized Aluminum + Steel is .30). This is a percent error lab so we could just be getting different answers due to human error.
Hi Strobot, Welcome to Physics Forums.

As you say, there are several possibilities for the particular types of metals you've got. That you've found an example where the known value accords with what you're seeing in the lab is encouraging, but not definitive. Being a percent error lab I think you'll be dealing
with error estimates and error propagation analysis in your calculations, right? Did you take note of error estimates for all your data readings?
 

FAQ: Finding the Kinetic Friction Force using Mass and Acceleration

What is kinetic friction force?

Kinetic friction force is the force that opposes the motion of an object as it slides or moves across a surface. It is caused by the microscopic roughness of the two surfaces in contact and is dependent on factors such as the type of surface, the force pressing the surfaces together, and the speed of the object.

How is kinetic friction force related to mass and acceleration?

The kinetic friction force is directly proportional to the mass of the object and the acceleration it experiences. This means that as the mass or acceleration increases, the kinetic friction force also increases. This relationship can be expressed mathematically as F = μkma, where F is the kinetic friction force, μk is the coefficient of kinetic friction, m is the mass of the object, and a is the acceleration.

What is the coefficient of kinetic friction?

The coefficient of kinetic friction is a dimensionless constant that represents the amount of friction between two surfaces in contact. It is specific to the two surfaces and is dependent on factors such as the material, texture, and temperature. The coefficient of kinetic friction is denoted by the symbol μk and is used in the formula for calculating kinetic friction force.

How can the kinetic friction force be measured?

The kinetic friction force can be measured by using an equation based on Newton's Second Law of Motion, F = μkma. The mass and acceleration can be measured using standard laboratory equipment, and the coefficient of kinetic friction can be determined through experiments or referenced from tables. The resulting value for the kinetic friction force will be in units of Newtons (N).

What are some real-life applications of finding the kinetic friction force?

Knowledge of the kinetic friction force is important in many real-life applications, such as designing brake systems for vehicles, determining the grip strength of tires on different road surfaces, and understanding the motion of objects on inclined planes. It is also relevant in everyday tasks such as pushing a cart or sliding a book across a table. Understanding and calculating the kinetic friction force can help improve efficiency and safety in various situations.

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