Analyzing Space-Time Trajectories: Rectilinear & Positive Velocity

[fabrc]

There's this graphic of space (s) versus time (t) of a particle.
How would I know if the trajectory is always rectilinear and if the velocity is always positive?

Observation: none of these "sentences" are true in this graphic. But I want to know how would I know these things if they were true.

 

[voko]

If "space" means "displacement from some point in a particular direction", then the fact that this displacement decreases at certain times should tell you something about the velocity in that direction.

You cannot deduce whether the trajectory is rectilinear from this, because you are simply not given enough information.

 

[fabrc]

Thanks, voko!

Sorry. So the term "space" is wrong? English isn't my natural language, and here in my country there's any good forums of physics.

 

[voko]

Have a look here:http://www.physicsclassroom.com/Class/1DKin/U1L1c.cfm