Orion 说:
Galileo's experiment was for proving that the rate of acceleration due to gravity is constant, rather than proportional to mass as Aristotle theorized.
Correct, the rate of acceleration due to gravity is a constant, however the rate of deceleration due to atmospheric friction is heavily dependent on mass, cross-section, and streamlining, as well as atmospheric density at that particular altitude. Depending on if and how a bullet tumbles as it falls, and at what angle it was fired, it may maintain a fairly high velocity, and CAN kill under the right circumstances (or wrong, depending on whether or not you're trying to kill someone/something with it). Terminal velocity is the balance point between gravitational acceleration and frictional deceleration.
An arrow has fletching to insure that it presents a tiny cross-section in flight, so it will be more likely to retain or regain speed as it drops (depending on the trajectory), and can be significantly more dangerous than a bullet if both are fired upwards. Dropping a pillow from a height would not be dangerous, since its huge cross-section compared to its mass would produce a much greater rate of deceleration due to friction, and therefore a much lower terminal velocity. Dropped from a great enough height in a vacuum, it could do massive damage.
As for the OP, the most reliable way to block an arrow with a sword, outside of tightly controlled and well-rehearsed conditions, would be to hold the blade up with the flat facing the archer. It covers a thin strip of your silhouette, and MIGHT be struck by an arrow fired in your direction, although the odds aren't good. Trying to hit an arrow in flight with a sword swing would be FAR less likely to stop or deflect the arrow, because you're adding a narrow time window to that narrow strip of coverage. Basically, it's only useful in movies and circuses.
