Falling objects are subject to the force of gravity, and as they fall their speed increases, or accelerates, by 9.8 m per second every second. This increase continues until the friction of the air becomes so great that acceleration stops and the object then fall at a constant speed.
Gravity produces the same force on any object, no matter how heavy or light it is. In a vacuum, a feather would fall and accelerate just as quickly as a brick. When a bullet is fired from a gun, the force of the explosion accelerates the bullet along the gun barrel. This force stops immediately the bullet leaves the gun, and friction begins to slow the bullet’s speed.
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