Friction between two blocks on a table

In summary, the conversation discusses two scenarios involving two blocks on a table and the forces acting on them. The first scenario involves the blocks at rest, with the static friction from the table counteracting the tension in the rope. The question is whether there is any static force being exerted by the bottom block on the top block, to which the answer is no. The second scenario involves the blocks in motion, with the bottom block exerting a kinetic force on the top block to oppose slipping. The question is which way this force acts and what force it is counteracting, with the answer being kinetic friction. The conversation also includes a discussion of a free body diagram and corrections made to it.
  • #1
burhan619
7
0
I have a question for two scenarios (see the diagram attached):

1) When the two blocks on the table are at rest, the static friction the table exerts on the bottom block is counteracting the tension in the rope, resulting in a net force of zero. Is there any static force being exerted by the bottom block on the top block? I don't think there should be any, since there is no horizontal force acting on the top block.

2) Suppose M was massive enough to start descending, overcoming the static friction threshold of the bottom block. Also suppose that the top block starts to slip away from the bottom block. Which way does the kinetic force the bottom block exerts on the top block point? And what's exerting the horizontal force it's counteracting?

Thanks in advance.
 

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  • #2
burhan619 said:
I have a question for two scenarios (see the diagram attached):

1) When the two blocks on the table are at rest, the static friction the table exerts on the bottom block is counteracting the tension in the rope, resulting in a net force of zero. Is there any static force being exerted by the bottom block on the top block? I don't think there should be any, since there is no horizontal force acting on the top block.
You are correct.

2) Suppose M was massive enough to start descending, overcoming the static friction threshold of the bottom block. Also suppose that the top block starts to slip away from the bottom block. Which way does the kinetic force the bottom block exerts on the top block point?
Friction acts in a direction to oppose slipping. Which way would that be?
And what's exerting the horizontal force it's counteracting?
What do you mean? This is kinetic friction.
 
  • #3
Is the free body diagram I've attached right?
 

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  • #4
here's a re-upload if that one's hard to see
 

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  • Untitled-1-01.jpg
    Untitled-1-01.jpg
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  • #5
burhan619 said:
Is the free body diagram I've attached right?
I guess the color coding is to tell which body the force acts on.

The forces on m1 look OK.

On m2, you forgot the kinetic friction from m1 and the normal force from m1. Otherwise, looks good.
 
  • #6
That makes sense. Thanks.
 

1. What is friction and how does it affect the motion of two blocks on a table?

Friction is a force that acts in the opposite direction of motion between two surfaces in contact. In the case of two blocks on a table, friction can either help or hinder their motion depending on the direction and magnitude of the force.

2. What factors affect the amount of friction between two blocks on a table?

The amount of friction between two blocks on a table is affected by the roughness of the surfaces, the weight of the blocks, and the force pressing them together. Additionally, the coefficient of friction, which is a measure of how easily the surfaces slide past each other, plays a significant role in determining the amount of friction.

3. Can friction be eliminated between two blocks on a table?

No, friction cannot be completely eliminated between two blocks on a table. It is an inherent property of surfaces in contact and is necessary for objects to stay in place and for controlled motion to occur.

4. How does the angle of the table affect the friction between two blocks?

The angle of the table can affect the friction between two blocks by changing the direction of the force of gravity. If the table is angled downwards, the force of gravity will act in the direction of motion, increasing the friction between the blocks. If the table is angled upwards, the force of gravity will act against the motion, decreasing the friction.

5. What are some real-life examples of friction between two blocks on a table?

Some common examples of friction between two blocks on a table include pushing a heavy book across a desk, sliding a furniture piece across a floor, or a car's tires gripping the road to move forward. In all of these cases, friction plays a crucial role in controlling the motion of the objects.

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