Time dilation due to velocity and time dilation due to acceleration are distinct phenomena, although they are both consequences of the theory of relativity.
Time Dilation due to Velocity (Special Relativity): According to special relativity, when an object moves at a high velocity relative to another object, time appears to slow down for the moving object as observed by the stationary object. This effect is known as time dilation due to velocity. The faster an object moves, the more pronounced the time dilation becomes. As the object's velocity approaches the speed of light, time dilation becomes significant. This effect has been confirmed by numerous experiments and is an essential aspect of special relativity.
Time Dilation due to Acceleration (General Relativity): In general relativity, time dilation can also occur due to acceleration or gravity. According to the theory, acceleration and gravity are fundamentally equivalent. When an object is subjected to acceleration or experiences a gravitational field, time appears to pass more slowly for the accelerated or gravitationally influenced object compared to a non-accelerating or weak gravitational field reference frame. This effect is known as time dilation due to acceleration or gravitational time dilation. The closer an object is to a massive gravitational source, such as a planet or a black hole, or the stronger the acceleration it experiences, the more pronounced the time dilation effect.
In summary, time dilation due to velocity is a consequence of special relativity and occurs when an object moves at high speeds relative to another object, while time dilation due to acceleration is a consequence of general relativity and occurs when an object experiences acceleration or is influenced by a strong gravitational field. Both effects have been observed and verified in experiments and are important aspects of the theory of relativity.