We did not get to this at lecture. We may briefly cover it next week else the text provides an excellent explanation that should be enough for you to be able to solve the homework problems
We end this weeks lectures with a brief introduction to the concept of vectors. How many of you know what a vector is. For a mathematician a vector is an oriented line segment. It has a length and a direction. Physicists use vectors to describe physical quantities which have a magnitude (the length of the vector) as well as a direction. Remember that in physics the magnitude comes with a unit as well. An example of where we need vectors is for describing motion in more than one dimension, which in fact is what we will be ambarking on next week. A vector simply points out a direction so in general you can move it around in space without changing its physical meaning. A special case is a position vector which always goes along with a specific choice of origin. The position is then the point reached from the origin when the position vector is drawn so as to start form there. Note however that we also use vectors to describe velocities acceleration and forces which are physical quantities with magnitude as well as direction.