Q1-I learned that different surface types have different frictions. Coarse(sp?) sandpaper could have more friction than the table top and waxpaper could have more friction than the table top.(See how it works? Other surfaces have different frictions than eachother-but it all depends on the wieght of what you're dragging across the surface!) Surface Area is also a factor in different frictions. Sometimes we pulled 2 blocks across a surface type and other times we pulled just 1 across the surface. Adding more mass contributes to adding weight and it's also a factor in friction force.
Q2-Becuase the spring scale is pulling the mass across the surface(My team used coarse(sp?) sandpaper), the friction force pulls it in the opposite direction, and the spring scale measures the friction that is happening.
Q3-there could be less friction than the table top becuase ice is pretty smooth. Try this-rub your hand against your dining room table or kitchen counter, then rub your hand across and ice cube. Big difference huh?