What are the molecular reasons that a smooth surface like Tiles have less friction than surfaces like asphalt with a material like rubber?

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There are two reasons why smooth surfaces like tiles have less friction than coarse surfaces like asphalt. The first reason is Newton's third law of motion. This law states for every action, there is an equal and opposite reaction. Anywhere objects collide, Newton's third law ensures that friction forces are at play. 

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There are two reasons why smooth surfaces like tiles have less friction than coarse surfaces like asphalt. The first reason is Newton's third law of motion. This law states for every action, there is an equal and opposite reaction. Anywhere objects collide, Newton's third law ensures that friction forces are at play. 

How strong a friction force is partially depends on how fine or coarse the surfaces are. Materials like asphalt are so coarse you can see ridges and valleys in the material with your naked eye. Materials like glass feel smooth, but have tiny ridges and valleys on the molecular level. As these hills and valleys come into contact with the hills on another surface, they have to push over each other. The steeper the hills, the more friction force is involved. 

But friction isn't primarily caused by surface roughness, which brings us to the second reason. Friction mostly occurs because of what are called weak electromagnetic forces. These are the forces of attraction and repulsion between charged particles, and they mostly dictate the strength of friction forces. On the atomic level, nothing is truly coming into contact. Particles are merely repulsing and attracting other particles, depending on how many charged, neutral, and uncharged particles can come into contact.

This is why smooth objects like rubber can still be great for producing friction; their chemical structure promotes electromagnetic forces. In other words, their surface has more contact with other surfaces on the atomic level.

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