# Finding the coefficient of friction of a block on a table

• ssj2pizza
In summary, the problem involves two blocks, A and B, connected by a pulley. Block B is set into downward motion and descends at a constant speed. The goal is to calculate the coefficient of kinetic friction between block A and the table top, expressed in terms of the weights of blocks A and B and the acceleration due to gravity. By setting the net forces on both blocks equal to zero and using a free body diagram, the solution is found to be the weight of block B divided by the weight of block A. The student struggled with finding examples of this type of problem in their book or notes.
ssj2pizza

## Homework Statement

Block A is on a table and is connected by a pulley to block B.
Block A has weight Wa and block B has weight Wb. Once block B is set into downward motion, it descends at a constant speed. Assume that the mass and friction of the pulley are negligible.

Calculate the coefficient of kinetic friction between block A and the table top.
Express your answer in terms of some or all of the variables Wa , Wb, and g (the acceleration due to gravity).

## Homework Equations

fk=$$\mu$$kn

I have gotten this hint (mastering physics problem):

In this problem, blocks A and B are in dynamic equilibrium; their velocities are constant. This means that the net force on each,F net , is equal to zero.

The tension is constant throughout the rope. By setting the sum of the forces acting on both blocks A and B equal to zero, you should be able to obtain two different expressions for the tension in the rope. Set these equal to each other and solve for $$\mu$$.

## The Attempt at a Solution

I really don't know how to go about starting this. I know the equation above but don't know what to do with it. I feel like I need to know the acceleration. How would I find the tension?

ssj2pizza said:
I really don't know how to go about starting this. I know the equation above but don't know what to do with it.

You don't know what to do with it? Haven't you ever seen a free body diagram? Don't you think it would be a good idea to draw one?

I feel like I need to know the acceleration.

You DO know the acceleration! In your very own words:

...it descends at a constant speed...

and

I have gotten this hint (mastering physics problem):

In this problem, blocks A and B are in dynamic equilibrium; their velocities are constant.

Ok so their accelerations were equal to zero and their net forces were also equal to zero. Thanks about the free boday diagram (duh). Well i figured out the answer. It ended up being the weight of block b divided by the weight of block a. I have tried looking in my book and looking through my notes but there were no examples for finding the coefficient of friction. (frustrating)

## 1. What is the coefficient of friction?

The coefficient of friction is a value that represents the amount of resistance between two surfaces when they are in contact with each other. It is a dimensionless value that ranges from 0 to 1, with 0 indicating no friction and 1 indicating high friction.

## 2. How is the coefficient of friction calculated?

The coefficient of friction is calculated by dividing the force required to move an object over a surface by the weight of the object. This can be done by conducting experiments or using mathematical equations.

## 3. Why is it important to find the coefficient of friction of a block on a table?

Finding the coefficient of friction allows us to understand the amount of force needed to move an object on a particular surface. This information is crucial in designing and building structures and machines, as well as predicting the motion of objects on different surfaces.

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

The coefficient of friction can be affected by several factors, including the smoothness of the surfaces, the weight of the objects, the type of material the surfaces are made of, and the presence of any lubricants or contaminants.

## 5. How can the coefficient of friction be reduced?

The coefficient of friction can be reduced by using lubricants, polishing or smoothing the surfaces, or changing the materials of the surfaces. Additionally, increasing the surface area of contact between the two surfaces can also reduce the coefficient of friction.

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