A cannon is a device for imparting a large velocity to a mass of iron, generally for the purpose of warfare. Over the centuries, the manufacture of cannons has taken many forms, but the basic construction has remained the same.
A cylinder (or barrel) is closed at one end (the breech) and open at the other (the muzzle). An explosive (or charge) is placed in the cylinder at the breech, and a ball is placed in the cylinder on top of the charge. The explosive is ignited and the reaction produces hot gases which increase the pressure. Thus the gases push the ball along the cylinder and out the muzzle at great velocity.
Beginning in the 1500s, gunners began using large-grained explosive in order to decrease the rate of burning. Faster burning charge creates a large pressure very quickly, thus creating stress on the cannon and creating a risk of failure. The slower burning charge ensures that the pressure behind the ball stays more nearly constant as the ball travels the length of the barrel.
For the following questions, consider a cannon which is 2.3 meters long with a bore (hole) of radius 5 centimeters. Assume the pressure inside the cannon after the explosive has been set off is constant. While the ball is in the cannon, the forces due to the gases are so much greater than the force of gravity that the force of gravity can be ignored.
Which of the following would best explain why a large-grained charge would burn more slowly than a small-grained charge?