What are the sign conventions for force in physical chemistry?

[hackerdiety03]

hey there! i am taking a physical chemistry course at my college. an assignment given was about miniature machines: "pulling" nanowires. one of the questions asked is concerning the types of sign conventions of force. i have tried to research this topic had have trouble finding out the different sign conventions. help!

 

[Astronuc]

Tension is considered positive, compression negative.

Force in the direction of motion is positive, force opposite direction of motion is considered negative.

Think of $F = m \ddot{x}$

Positive F should yield positive acceleration, negative force yields deceleration.

With respect to pressure (force per unit area), force in direction of surface normal would be positive, force opposite direction of normal would be negative.

 

[hackerdiety03]

so these are considered the sign conventions of force? the positive/negative signs depending on the direction of the force of the object and other conditions?

 

[Astronuc]

Basically, yes.

Force and acceleration are vector quantities - and being so, they have magnitude and direction. The magnitude is always positive. The use of (+) and (-) relates to the direction in which the force is applied.