The blue arrow shows velocity — its direction tells you which way the car moves; its length tells you how fast.
The red arrow shows acceleration — the direction the velocity is changing toward. It is independent of velocity.
When the arrows point the same way, the car is speeding up. When they point opposite ways, it is slowing down — even though acceleration is not zero.
| v | a | result |
|---|---|---|
| + (right) | + (right) | faster rightward |
| + (right) | − (left) | braking, then reverses |
| − (left) | − (left) | faster leftward |
| − (left) | + (right) | braking, then reverses |
Drag the sliders — or use ◀ ▶ arrow keys — to explore all four cases.