Coffe Filter Terminal Velocity (Drag Lab)

Before this lab, we gathered as a class to discuss important ideas, and after our teacher's very important story of when he went skydiving with the jumpmaster and learning complex techniques like "the bellybutton banana" we went on to our normal routine of testing ideas through a lab.  We talked about how in skydiving the person accelerates down for a period of time, but after a while they stop accelerating and keep a constant, terminal velocity, but what makes this happen?  Well we know that if there is no acceleration, then all forces must be balanced, so what is counteracting the force on the earth pulling the skydiver downward.  As a class, we came to the consensus that it is air resistance creating a force strong enough to push up with as great of a force as is pushing down on the skydiver.  We wanted to learn more about the air resistance, yet without a plane we were stuck, so we decided to take coffee filters that we could measure the surface area and mass to test what the terminal velocity is.



We did two labs, one where we kept the mass the same but changed the surface area, and the other where we changed the mass but not the surface area.  When we kept mass constant we needed to start with 6 coffee filters stacked up and taped together, then used a motion sensor to find the terminal velocity, but changed the surface area by then making 2 stacks of 3 coffee filters and taping together (with the same amount of tape to keep the mass constant) then 3 stacks of 2 and finally 1 stack of 6.  We recorded our data and moved on, and with our second lab we just used one stack but added mass by merely stacking more and more coffee filters on.

Using what we learned from this lab and our previous knowledge, we decided that adding mass makes the terminal velocity higher, which makes sense as a higher mass would then mean a higher force of the earth on the object and to balance that force, the velocity must be higher.  However, we also found that surface area was inversely related to terminal velocity, so as it grew, the terminal velocity shrunk.  This also makes sense as why when parachutes shoot out they slow skydivers down by adding surface area.  With this in mind we realized when air resistance is added, not all objects fall at the same rate, only if they have a proportionate mass and surface area.  To learn more about terminal velocity, visit this video: https://www.youtube.com/watch?v=x4_dFDEpAaI and see how we found the terminal velocity of a ball without dropping it.  Thanks and I'll see you next time, probably a couple days before our third quarter ends and grades are due.