A block slides to the right on a rough horizontal surface. The forces exerted on the block are shown above. Which of the following statements about the frictional force Ff exerted on the block is true? A) It is the only force acting on the block that is caused by microscopic interactions.

B) It does not depend on the materials that the block and the surface are made of.

C) It is caused by gravitational interactions between the atoms in the block and the atoms in the surface.

D) It is the sum of all the microscopic contact forces between the bottom of the block and the surface.

The characteristics of the friction force, you can find which statements are correct:

   D) It is the sum of all the microscopic contact forces between the bottom of the block and the surface.

The force is an image of the interactions between bodies, these interactions create binding energy that can be formed and broken, the friction force is the macroscopic sum of all these microscopic interactions between two different surfaces.

The magnitude of the friction force depends on the type of each surface, on rough surfaces the interaction area is high, therefore the friction force is high, on smooth surfaces the interaction area is small, therefore the force is small, a way to create superficiality is to place a layer of air between the two surfaces.

Based on these explanations, let's review the different statements:

A) False. The friction forces are caused by interaction, but between two bodies not within the same body, this is what maintains the shape and volume of the body.

B) False. The contact area depends on each surface and therefore each type of material

C) False. The gravitational force is this in the line of interaction between the two bodies, in this case the force is perpendicular to movement, not in the line of interaction.

D) True. It is the sum of the interactions in the contact between the two bodies, it agrees with the explanation above.

Using the characteristics of the friction force, we can find the statements that are correct is:

   D)  It is the sum of all the microscopic contact forces between the bottom of the block and the surface.

Learn more about friction force here: link

The correct option is;

A) It is the only force acting on the block that is causes by microscopic interactions

Explanation:

The force of friction is the force due to the relative motion of two surfaces in the presence of a perpendicular force acting between the surfaces.

The force of friction comes into play from the additional effect of the adhesion that is present between surfaces, the roughness of the surfaces, the contamination or deformation of the surfaces which is generated by the microscopic interactions be between the two surfaces, rather than the applied force.

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