Answer:
- circular motion
- motion of light (photons) on a non-linear path
Explanation:
Velocity is a vector with speed and direction components. If the speed does not change, then the direction must. In order to change the direction of a velocity vector, there must be some acceleration, and it must be orthogonal to the direction of motion.
Circular motion is motion that has a constant acceleration perpendicular to the direction of travel.
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Another kind of motion that meets the requirement is the motion of light. Light travels at a constant speed, regardless. If light changes direction (as in a gravitational field or when reflected), its direction will change, but its speed will not.
