The gravitational acceleration decreases with altitude, as shown by the solid line in Figure 1 (left). g is equal to 9.5 m/s2 at 100 km altitude, which is 9% larger than 8.7 m/s2. However, at 500 km altitude, g is close to 8.45 m/s2, which is close to 3% smaller than 8.7 m/s2. When R becomes less this value also decreases. Hence, acceleration due to gravity decreases with increase in depth. A change in velocity is either a change in an object's speed or its direction and when a moving object changes direction, its velocity changes and it is accelerating.