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# Modelling air resistance

I have to submit a Lab report tomorrow and i dont have a clue

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I'm not sure what the teacher expects from you, but getting an accurate model of air resistance - or at least verifying an existing model - isn't easy to do experimentally. Since the resistive force depends on the velocity, the force changes as the object decelerates.

I suppose a simple experiment could look at, say the surface area of an object and it's time taken to fall a certain distance. It wouldn't give you much in terms of meaningful data, but you could analyse it and see if it fits any standard curve.

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I sort-of did this for my EE.  At low velocities, the magnitude of the force of air resistance is approximately the speed times a constant.  At higher velocities, the magnitude of the force is the speed squared times the cross sectional area times some constant.  If you can track the trajectory of the object (ie, set a camera perpendicular to the plane of motion, and then plot the object in logger pro), you should be able to figure out the acceleration with the second-time derivative, and then by extension the force, and then after adjusting for gravity, deduce the drag equation with some differential equations a little bit outside the scope of IB physics.  Or just plot the air resistance (taking out gravity) and do a curve fit.  Meh.

Now, a good scientific model should be able to make accurate predictions, so you could test the validity of your curve-fit by seeing how accurately it estimates the trajectory of the object with different initial conditions.  Of course, if the prediction fails miserably, you could just...not include that part in your report.

^this is all assuming I did my EE correctly.  I never really got a chance to ask my adviser about those calcs, so there's the very real possibility that I'm completely wrong.