Getting drag

When I heard that my maths assignment would be in part, about calculating the coefficient of air resistance of an object with and without a parchute (i.e. comparing the two), I couldn’t help but extend the assignment a bit further.

Tada! figure figure

Despite my incompetence in soldering (though I don’t think I’m too bad) I managed to stick a cheap SD card reader with a Teensy 3.1 and Invensense MPU-6050 (6 DOF IMU - essentially a 3 axis gyro + accelerometer) onto a small board, due to size constraints.


Essentially the module fits inside a plastic cylinder with a rounded nose tip. A simple parachute made of a plastic bag is stowed also in the cylinder and only taken out when in use. Unfortunately the object broke after a few 11 m drops from the outside the biology rooms and I threw it in the bin without thinking twice. Moral of story: take photos before you throw something off a building.

I’m not sure whether I’m allowed to post any part of an assignment online, so it’d probably be better if I didn’t (in case they use the assignment every again). Essentially, you can use some numeric integration of acceleration to estimate velocity at any time, t. However, as there’s a lot of error due to the error of accelerometers and integration over time (even a super small error in accelerometers can accumulate to a lot of error), this is much better as a timing tool to time the drop instead of using a stopwatch.

After calculating the coefficients of air resistance, I found that the parachute decreased the terminal velocity of the object by 89%. Surprising? Not really.

No extra marks for extra work :( oh well.