There can be only subjective answers to your question. There is no "lowest," since it depends on how you define "significant," but 0.5c is usually considered to be the point were the rate of change begins to take off rapidly.
bandwidth
5mph
5 strokes
water.
0 MPH
A fraction of the speed of light can range from 0 to just under 1. For example, half the speed of light would be 0.5c, a quarter would be 0.25c, and so on. The speed of light in a vacuum is approximately 299,792 kilometers per second.
In the film 'Interstellar', the spacecraft called Endurance travels at a significant fraction of the speed of light, specifically around 90% of the speed of light, which is approximately 270,000 kilometers per second.
21/25
The state with the lowest average wind speed is typically Florida, as it is known for having calmer weather conditions compared to other states.
Solids.
1/500
A complete stop.