# Find the kinetic friction coefficient

In summary, the conversation is about solving an exercise involving three blocks and their resulting acceleration. The solution involves considering the total mass of the system and drawing separate force-body diagrams for each block. The conversation also discusses the relationship between forces applied to block 2 and the tensions in the strings, which are not equal to the weights of the suspended masses.
Homework Statement
See image1.
Block 1: 1M kg
Block 2: 2M kg
Block 3: 2M kg
Resulting acceleration: .5 m/s2
Relevant Equations
F = ma
fk = Fn * u

Image1, the exercise.

My solution:

Image2, my solution

The answer is .37 but I keep getting .45
What am I doing wrong?

Homework Statement: See image1.
Block 1: 1M kg
Block 2: 2M kg
Block 3: 2M kg
Resulting acceleration: .5 m/s2
Homework Equations: F = ma
fk = Fn * u

View attachment 250394
Image1, the exercise.

My solution:
View attachment 250395
Image2, my solution

The answer is .37 but I keep getting .45
What am I doing wrong?
What's the total mass of the system?

5M but I don't see your point?
I use F=ma on the center block (block 2), what does the total mass have to do with anything?

what does the total mass have to do with anything?
All blocks will accelerate together, so their total mass is the total inertia.
Alternatively, assign unknowns to the tensions and draw a separate FBD for each block.

It produce the correct answer, but I still don't see the corelation.
I mean we only look at forces applied to Block 2, but for some reason we need to consider the mass of the two other blocks aswell?

I mean F (from F=ma) here is applied only to block 2, its not applied to block 1 or 3. If it were they'd all move sideways. How come m should include block1 and 3 then?

I mean we only look at forces applied to Block 2
But did you? The forces on block 2 are the tensions in the strings. They are not equal to the weights of the masses suspended on the ends.
As I wrote, draw separate FBDs for each block, treating the tensions as unknowns.

## What is the kinetic friction coefficient?

The kinetic friction coefficient, also known as the coefficient of kinetic friction, is a constant value that represents the amount of friction between two surfaces in motion. It is denoted by the symbol μk and is a unitless quantity.

## How is the kinetic friction coefficient measured?

The kinetic friction coefficient can be measured experimentally by using a device called a friction tester. This device applies a known force to an object and measures the resulting friction force. The ratio of these two forces gives the value of the kinetic friction coefficient.

## What factors affect the kinetic friction coefficient?

The value of the kinetic friction coefficient depends on several factors, including the nature of the surfaces in contact, the force pressing the surfaces together, and the presence of any lubricants or contaminants.

## How does the kinetic friction coefficient differ from the static friction coefficient?

The kinetic friction coefficient is the measure of friction between two surfaces in motion, while the static friction coefficient is the measure of friction between two surfaces at rest. The kinetic friction coefficient is typically lower than the static friction coefficient for the same two surfaces.

## Why is the kinetic friction coefficient important?

The kinetic friction coefficient is an essential concept in physics as it helps determine the amount of work and energy needed to overcome frictional forces. It also plays a crucial role in understanding and predicting the motion of objects in various situations, such as sliding, rolling, and fluid resistance.

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