To understand Boyle's law, it helps to visualize the behavior of gas particles (or molecules) in an enclosed space. In a closed container, individual molecules are constantly hitting and bouncing off the container walls. Each time a gas molecule bounces, it imparts a force on the wall.1 In a flexible container such as a balloon, the force of the molecules hitting the inside of the balloon hold the balloon inflated. The force of each impact is small, but the sheer number of collisions create enough force to keep the balloon open.2