Final answer:
The positive sign in an op amp indicates the non-inverting input, meaning the output will have the same phase as the input. In physics, a positive sign for acceleration indicates motion in the direction of the positive axis. Numerically, a positive sign indicates a value greater than zero.
Step-by-step explanation:
When discussing an op amp (operational amplifier), the positive sign typically refers to the non-inverting input terminal. This is the point where the input signal is applied if amplification without phase inversion is desired. In other words, when a signal is input into the positive terminal of an op amp, the output signal will retain the same phase as the input. If the input voltage increases, so does the output and vice versa.
The significance of the positive sign can be understood in other contexts as well. For instance, in the case of physical motion, a positive acceleration means that the object is speeding up in the direction of the positive axis defined by the coordinate system. If a train has a negative velocity but a positive acceleration, this indicates that the train is decelerating—that is, it's speed is decreasing as it moves to the left and the positive acceleration is opposing its motion.
Lastly, the positive sign is also a numerical indicator that a number is greater than zero. The absence of a sign conventionally means a number is positive as well.