2.1.2—Distance, displacement, speed, velocity and acceleration

Velocity v=ds/dt is the rate of change of displacement; acceleration a=dv/dt is the rate of change of velocity. Their signs depend on the chosen direction.

A negative velocity can mean motion opposite to the positive axis, while negative acceleration does not automatically mean slowing down—compare signs of v and a.

If v is positive and a negative, the object slows until v reaches zero; if both are negative, speed can increase.

Acceleration opposite to velocity means slowing only while the velocity remains in that direction.