# confusion on vector quantities

How can we define simply that velocity is a vector quantity without mentioning that velocity has vector properties. How can we simply say it needs both magnitude and direction for its complete description? Well for magnitude it is clear but for direction being a necessary for its complete description I found it hard clear the concept on the subject?

• That's just a definition. Are you saying you don't like it? – auxsvr May 4 '14 at 12:26

I will ask you a simple question. You are moving with speed $5m/s$ and I'm moving with speed $10m/s$. What is my relative speed from your point of view? Immediately you first reaction is: "I cannot answer because I have no idea if you are moving in my direction or away from me." And that would be correct, because the answer changes, it depends on the direction. If I'm moving away from you, the answer is $10 + 5 = 15 m/s$. If I'm moving in your direction the answer is $10 - 5 = 5 m/s$. This is why we say velocity has magnitude (e.g $5m/s$) and direction (e.g away from you etc.), to avoid confusions like this.