When we want to compare two quantities a and b, but both are measured quantities such that neither can be considered to be an exact value, we use a "percent difference." percent difference is calculated by taking the absolute value of the difference of the values divided by their average multiplied by 100, or a-b % difference = 100% for example, in a measurement where no calibrated speedometer is present, we measure two values of speed, ua-10.0 m/s ± 1.1 m/s and = 12.0 m/s ± 1.3 m/s. calculate the percent difference of the two speeds above.

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.