Прискорення та сповільнення

The terms "speeding up" and "slowing down" are commonly used in physics classes and in general life. But some people don't understand what they physically mean. They are dependent on the position of the particle that is "speeding up" or "slowing down." In particular, these terms pertain to the acceleration of the particle--the second derivative of its position. So if $p(t)$ is the position function for the particle, then

If $a(t) = p''(t) > 0$, the particle is speeding up.

If $a(t) = p''(t) < 0$, the particle is slowing down.

If $a(t) = p''(t) = 0$, then the particle is moving at a constant speed.