When a wooden ball is thrown upwards and then allowed to fall, it experiences constant acceleration due to gravity throughout its motion. The acceleration remains non-zero as long as the ball is in the air, calculated as a = Fgrav/m. Only when the ball is held or when the ground exerts a normal force does the net force become zero, resulting in no acceleration. Thus, the ball accelerates downwards during its entire free fall. Understanding this principle is crucial for solving problems related to motion under gravity.