You push a book across a table. The book moves at a constant speed, but you do not move. What is the net force on the book?

What does si stand for, when referring to a system of measurement

Suppose that three astronomical objects, 1, 2, and 3 are observed to lie on a line, and the distance from object 1 to object 3 is d. object 1 has four times the mass of object 3, and seven times the mass of object 2. find the distance between objects 1 and 2 for which the net force on object 2 is zero.

Which pair of quantities includes one quantity that increases as the other decreases during simple harmonic motion?