# A level maths

Hi,guys.I have a question here! While doing suvat problems of vertical motions,how exactly do I assign the sign conventions?For example,suppose a particle P is moving upwards from a fixed point O and a particle Q is moving downwards.Here,do I assign different sign conventions for P and Q?For example,for P,I take upwards as positive,and for Q,I take downwards as positive.Is it the case?
It does not matter whether you take 'up' or 'down' to be the positive direction, what matters is that you are consistent. So if you take up to be the positive direction, then any particle moving downwards has negative velocity. Similarly if you take down to be the positive direction, any particle moving up has negative velocity. I.e. two particles moving in opposite directions cannot both have positive velocity, since velocity is vector valued and is determined by both speed and direction.
(edited 10 months ago)
Original post by Zebedi1
It does not matter whether you take 'up' or 'down' to be the positive direction, what matters is that you are consistent. So if you take up to be the positive direction, then any particle moving downwards has negative velocity. Similarly if you take down to be the positive direction, any particle moving up has negative velocity. I.e. two particles moving in opposite directions cannot both have positive velocity, since velocity is vector valued and is determined by both speed and direction.

okay so that means the direction that I assign to be positive or negative will apply to two objects simultaneously??
Original post by Anlasan
okay so that means the direction that I assign to be positive or negative will apply to two objects simultaneously??

Yes, direction is immutable. Only one direction can be described as positive for all objects in a scenario.
Original post by zebedi1
yes, direction is immutable. Only one direction can be described as positive for all objects in a scenario.

thank you soo much for clearing my confusion!!!