Fill in the Blanks P1H Ch 04 HW 01 RNAOnline version P1H Ch 04 HW 01 RNA by rpedelty 1 O The main idea of this chapter is quite simple : Horizontal and vertical motion are . A ball thrown horizontally continues to move with the same speed in the direction , even as it falls with an increasing speed in the direction . The of a vector are the key to understanding the independence of horizontal and vertical motions . Of all the mathematical tools used in this book , none is more important than the . In fact , vectors are indispensable in describing many of the key quantities in physics , like , , and . Sometimes a scalar isn't enough to adequately describe a physical quantity . There are many cases where a is needed as well . A vector is a quantity that is specified by both a and a . The length of a vector is referred to as its . When we indicate a vector on a diagram or a sketch , we draw an . It is common in handwritten material to draw a over the vector's symbol , which is very similar to the way vectors are represented in this text .