* Increasing Speed: When the rider pedals harder and the bike goes faster, they are accelerating.

* Decreasing Speed: When the rider applies the brakes and slows down, they are also accelerating. This is called deceleration or negative acceleration.

* Changing Direction: Even if the rider maintains a constant speed, if they turn or change direction, they are accelerating. This is because acceleration is a change in velocity, and velocity includes both speed and direction.

In summary: A bicycle rider is accelerating any time their speed or direction is changing.