A key principle used in aviation is Bernoulli's principle, which states that the faster air moves, the less pressure it exerts on its surroundings. This is how an airplane wing achieves lift, by air moving over it faster than air moving below it, and the higher air pressure below pushing up on the wings. Kids can demonstrate Bernoulli's principle by hanging two soda cans about 5 inches apart. When they blow between the cans, the cans will move together, pushed by the greater air pressure of the still air around them.
Objects in air and water have buoyancy, which is the upward force of the fluid around them. Archimedes determined that the buoyant force is equal to the weight of the fluid displaced. This is how materials heavier than their medium (like a steel boat in water or a hot air balloon made of materials heavier than air) can float. Kids can demonstrate that the same amount of material will float better depending on how much water it displaces. They can make a boat out of aluminum foil, then change the size to a smaller boat to see how small the boat can be (and how little water it can displace) and still be lifted by the buoyant force.
Hot air balloons gain the lift to rise by becoming less dense than the air around them. Students can demonstrate this lift by making a hot air balloon out of a large garbage bag or tissue paper. Once the balloon is constructed, use a hair dryer to blow warm air into the balloon. Even though the balloon stays the same size, the less dense hot air will fill the space and eventually weigh less than the surrounding air. The balloon will then float to the ceiling.
Parachutes take advantage of aerodynamic principles to keep something falling more slowly than gravity would otherwise make it. Students can use various materials (e.g.,tissue paper, plastic bags and aluminum foil) in different shapes (e.g., round, square, oval or triangular) to make the most effective parachute for a small action figure or toy.
While thrust in aerodynamics is the force that causes forward motion, drag is the force that works against it. In airplanes, drag is caused by air. In boats and submarines, drag is caused by the water. Students can race and record times of toy cars (or toy boats in water) with different body shapes across a distance to see which ones have the least drag. Suggestions include testing whether a streamlined body is better than a bulky body, if a pointed front causes less drag or if solid material or permeable cloth is more aerodynamic.