What causes friction between two seemingly smooth surfaces?

a. the surfaces really aren't smooth. it's just an illusion.

b. surfaces that are too smooth tend to stick together.

c. tiny collisions on the surfaces, called microwelds, cause friction.

d. there is an invisible force sticking the surfaces together.

Your 249 ml cup of coffee is too hot to drink when served at 82 degree celsius. what is the mass of an ice cube taken from a -21 degree celsius freezer, that will cool your coffee to a pleasant 54 degree celsius. specific heat of the water is 4190 j/kg c, specific heat of ice is 2090 j/kg c, heat of fusion of ice is 3.33 x 10^5 j/kg

Which articulations allow for greatest range of motion?

Apair of 10μf capacitors in a high-power laser are charged to 1.7 kv.a. what charge is stored in each capacitor? b. how much energy is stored in each capacitor?