- Let’s adopt the “rightward is positive” convention for the motions below
- Since the sheep is moving rightward and speeding up, its velocity is represented by more and more positive numbers.
- Since the velocity is becoming more positive, the acceleration is positive.
–
- Since the sheep is moving leftward and speeding up, its velocity is represented by more and more negative numbers.
- Since the velocity is becoming more negative, the acceleration is negative.
–
- Since the sheep is moving rightward but slowing down, its velocity is represented by less and less positive numbers.
- Since the velocity is becoming less positive, the acceleration is negative.
–
- Since the sheep is moving leftward but slowing down, its velocity is represented by less and less negative numbers.
- Since the velocity is becoming less negative, the acceleration is positive.
- In a nutshell, the speed increases if the velocity and acceleration have the same sign, and decreases if the velocity and acceleration have opposite signs.