Obtain and weight a balloon and small weight (ie paper clip). Inflate the balloon to a bit less then the size of your head and measure the circumference of the ballon. Set up a Vernier Comp on a metal bar near the ceiling of the lab. Now hold the balloon close to the Vernier comp with the weight on the bottom of the balloon to try and keep it from spinning. Holding the balloon close to the Vernier comp start recording and release the balloon about a second after you start recording. Once the balloon hits the floor stop the recording and analyze the graphs. The graphs should look smooth and the velocity graph should start to curve up to a plateau.
If the graph does not have a similar shape to the sample graph above but has a curve but not the plateau you will need to lose some weight (but you will need some weight to keep the balloon falling straight) or add more air to make the balloon bigger so it falls more slowly. This plateau is the terminal velocity of the balloon or the max velocity the balloon will reach on its way down. From the table made by the computer from the graphs take the velocity values and find the drag force at different time intervals by using newton’s second law Fnet=ma which will become Fd+Fb-Fg=ma after all the forces are taken into account where Fd is the drag force, Fb is the buoyant force, and Fg is the force of gravity. With these different drag values you found and the velocities you took earlier plot a drag Vs. velocity graph with drag on the y-axis. This graph can either be parabolic or linear in shape. Use excel to calculate and make the graph as it will make a much more accurate graph. From this Drag vs. Velocity graph find the slope of the line which is the coefficient of drag for the particular balloon you made.