- #1
Jimmy87
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Homework Statement
I collected data for an experiment involving air resistance. We made paper disks and timed how long they took to fall over a fixed distance. We changed the radius of the disk. We found that as you increase the radius they take longer to fall. I am trying to explain my results but with some difficulty.
Homework Equations
The Attempt at a Solution
We have been taught about forces expeienced by falling object e.g. weight and drag. I was thinking that if you double the radius of the circle then the area will increase by a factor of 4 which means the weight force will increase by a factor of 4. Since we found that it took longer for a bigger radius, the air resistance must not be proportional to the area. We have not been given any equations for air resistance but I did some research and found this one (https://en.wikipedia.org/wiki/Drag_equation). You can see that the drag force is in fact proportional to the surface area. However, if you double the radius the area should increase by a factor of 4 which means the weight will increase by a factor of 4 but according to this equation so should the drag force which means a paper circle of a bigger radius should take the same time to fall. What am I missing here? I know I am missing somehting because if this were true then for a given material e.g. a parachute it wouldn't matter how big you make the surface area and we all know that it does.