Final answer:
In free fall, upward motion is usually considered positive while downward motion is taken as negative. The acceleration due to gravity has a constant value of -9.8 m/s², indicating that the positive direction is upward according to the conventional coordinate system used in physics. This convention helps ensure consistency in problem-solving.
Step-by-step explanation:
In free fall, the designation of positive and negative direction is usually based on the chosen coordinate system. Typically, upward motion is considered positive and downward motion is negative. When dealing with the acceleration due to gravity (g), which is approximately 9.8 m/s², it can be assigned a negative value when taking downward as the negative direction, leading to g = -9.8 m/s². This means that in free fall, the direction of acceleration due to gravity is always downward, regardless of the object's motion. As an object is launched upward, its velocity will decrease until it reaches its peak (zero velocity), and then it will increase in the negative direction as it falls back to the ground.
This method aligns with the description in Figure 2.7, where upward or rightward motion is considered positive, and downward or leftward motion is negative. This standard is useful in solving physics problems and ensures consistency. Whether an object is moving upwards or downwards, it experiences the same acceleration due to gravity throughout its trajectory. Moreover, in Einstein's thought experiments, such as the one with two people freely falling into a chasm, both would accelerate downward at the same rate, indicating the universality of gravitational acceleration in free fall.