Apart from the roughness of the surfaces rubbing together, identify one other variable that increases the size of a friction force.
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Answers
# The friction force depends on two factors:
a) The materials that are in contact. The two materials and the nature of their surfaces.
b) The force pushing the two surfaces together. Pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other.
Answer:
Political conversations with family, for one.
“Friction” is a blanket term to cover all of the wide variety of effects that make it difficult for one surface to slide past another.
There a some chemical bonds (glue is an extreme example), there are electrical effects (like van der waals), and then there are effects from simple physical barriers. A pair of rough surfaces will have more friction than a pair of smooth surfaces, because the “peaks” of one surface can fall into the “valleys” of the other, meaning that to keep moving either something needs to break, or the surfaces would need to push apart briefly.
This can be used in hand-wavy arguments for why friction is proportional to the normal force pressing surfaces together. It’s not terribly intuitive why, but it turns out that the minimum amount of force, Ff, needed to push surfaces past each other (needed to overcome the “friction force”) is proportional to the force, N, pressing those surfaces together. In fact this is how the coefficient of friction, μ, is defined: Ff = μN.
Explanation: