Here, 'displacement' refers to that from the starting position.
When 'Edit v-t graph' is selected, the v-t graph is capable to be changed
by dragging the red corner points on the graph upward or downward.
The slope of displacement-time graph is velocity; the slope of velocity-time graph is acceleration. Uniform
acceleration is the case when the acceleration is a constant,i.e. the
velocity changes at a constant rate.
Negative acceleration is usually called "deceleration". In fact, we need both the
directions of velocity and acceleration to determine whether the object
is speeding up or slowing down. The following table summarizes the four cases:
Velocity
Acceleration
Status
Positive
Positive
Real acceleration (moving in the positive direction and speeding up)
Positive
Negative
Real deceleration (moving in the positive direction and slowing down)
Negative
Positive
Real deceleration (moving in the negative direction and slowing down)
Negative
Negative
Real acceleration (moving in the negative direction and speeding up)
In short, object slows down when the acceleration is opposite to the velocity.