# Displacement !

1. Dec 9, 2008

### saikrishnadee

What do you mean by displacement has direction . When we generally mention in a problem then we just tell 20m , not 20m N ! So what actually do you mean by direction

And there's sumthing like this right

scalar x scalar = vector

How many equation like that are there ?

2. Dec 9, 2008

### Staff: Mentor

In physics, displacement is a vector. Moving 20m North is quite different from moving 20m East! But sometimes direction doesn't matter.

Don't know about that. Do you have a specific equation in mind?

3. Dec 9, 2008

### Georgepowell

Usually when we talk about a vector quantity, we make it negative or positive depending on its direction. And "20m" on its own is not a vector quantity, unless you have already stated that a positive distance means north (and a negative one means south).

You are right: "20m" is a distance (scalar), "20m N" is a displacement. Just sometimes the "N" is not actually written, it is just known in your head, or drawn on a diagram.

This only covers one dimensional vectors, where only two directions are taken into account.

If you have a two dimensional plane, and you have a force, F, acting in a peculiar direction. Then you could either say:

1. The force F = (3i + 4j)N *
2. F = 5N at an angle of about 53 degrees.

* N is not North, N is newtons in this context. And the i and j are "perpendicular unit vectors". What this basicly means is that the force F is equivalent to two seperate forces: one of them is 3 newton left, and the other is 4 newtons Up.

Both 1 and 2 are valid ways of writing the same vector force.

As for scalar*scalar = vector

Im not sure, I know you get scalar*vector=vector
e.g. F=ma, The direction of F is exactly the same as the direction of a.

and vector*vector=vector

v=at (velocity = acceleration*time, if the initial velocity is zero)

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