Background Paragraph: All fluids exert pressure like the air inside a tire. The particles of fluids are constantly moving in all directions at random. As the particles move, they keep bumping into each other and into anything else in their path. These collisions cause pressure, and the pressure is exerted equally in all directions. When particles are crowded together in one part of an enclosed space, such as the air particles first entering a tire, they quickly spread out to fill all the available space. That’s because particles of fluids always move from an area of higher pressure to an area of lower pressure. This explains why air entering a tire through a tiny opening quickly fills the entire tire. 
Story: Catherine is throwing her friend a birthday party and is starting to put up decorations. She has finished hanging streamers and now she has to fill the balloons. Having never used a helium tank before, she wants to test how much to fill each balloon.
If Catherine filled two balloons and one expanded more than the other does the larger balloon have higher or lower air pressure? If Catherine filled two balloons and one expanded more than the other does the smaller balloon have higher or lower air pressure? If a balloon pops has Catherine increased its air pressure too much or not enough? If a balloon stops expanding while being filled will adding more helium increase or decrease the pressure? If it only took two seconds to fill a balloon at first, but now it takes three seconds has the tank pressure increased or decreased? If one balloon is full and another is only half full does the full balloon have a higher or lower pressure? If one balloon is larger than another will it require more or less helium to fill? If one balloon is smaller than another will it require more or less helium to fill? If the pressure gauge on the helium tank is high will the helium leave the tank more quickly or more slowly than if it were low? If the pressure gauge on the helium tank is low will the helium leave the tank more quickly or more slowly than if it were high?