May 07

Wind Tunnel and Wiffle Balls

Maverick drops wiffle ball in wind tunnelMaverick’s interest in flying saucers led us to studying fundamentals of aerodynamics.  We dropped wiffle balls into a vertical wind tunnel made from a shop vac and sliced 3-liter soda bottles.  The balls behave differently, usually hovering at one of two heights, so we took 3 balls, weighed them, inspected their surface (noticing some had smooth seams and others a lip), and noted their color.  We then dropped each into the wind tunnel (already blowing) 10 times, noting the hover height.weight of wiffle ball

The 15.6 gram blue ball hovered at 6″ four times, 26″ once, and 27″ five times.  The 15.8 g green ball hovered at 6″ six times and 27″ four times.  The 13.7 g orange ball hovered at 22″ once and 27″ nine times.  We looked for patterns, noticing that lighter balls tended to hover higher, exposed seams might cause balls to drop to a lower hove, and color was not controlled.  So we took another 3 balls of the same colors and weighed and inspected them.  We dropped each of those 10 times into the wind tunnel.

wiffle ball seamsThe 15.2 g blue ball hovered at 6″ twice, 26:” once, and 27″ six times.  The 15.9 g green ball hovered at 6″ nine times and 27″ once.  The 13.4 g orange ball hovered at 6″ once, 15″ once, 20″ once, 26″ once, and 27″ six times.  Between the two sets of balls color and weights correlate, so we can’t yet separate those even though we strongly believe that color should not affect aerodynamics.  To distinguish color and weight, we could attach weights, such as pieces of masking tape, to equalize weights, but we’d have to be careful to not impact aerodynamics with the tape.  Although weight appears to affect hover height, the lightest ball (Orange run 2) averaged lower hover heights than the 2nd lightest ball (Orange run 1).

data of wiffle ball height in tunnelThis is prelude to testing the impact of covering holes on the wiffle balls and measuring aerodynamic impact.  Most encouraging for me is that Maverick had the patience and tenacity to run 60 tests. Judging science fairs and teaching science, I see few students eager to persist after a few runs…but that just gives impressions, not supporting data.  I look forward to continuing this exploration of aerodynamics!

solar animation and chaotic pendulumBefore we started with the wind tunnel, we played with animated solar toys: dancing flower, swinging bear, flapping turkey, and fluttering butterfly.  We compared the fluttering butterfly with a chaotic pendulum when Maverick thought the obvious magnet stuck to the thorax of the butterfly might be interacting with a similarly fixed magnet hidden in the flower.  The differing behavior of the chaotic pendulum, which we configured with a repelling magnet directly under the magnetic pendulum suggested something different going on with the butterfly.

Since its motion was most interesting and its case easiest to pry apart, we opened the dancing flower to find the solar panel powering an integrated circuit, which controlled an electromagnet.  We opened the swinging bear, too, to find an voltage from solar flowerintegrated circuit setup the same in appearance, possibly identical.  We suspected that the integrated circuit turns the electromagnet on and off, so we tried to measure that with a multimeter.  While we did get a 1.6 volt reading from the solar panel, the wires to the electromagnet were very, very small, making it hard to maintain electrical connection with the multimeter probes long enough to measure.  Our make and break contact, due to hand shake, hid any periodicity we might measure of the integrated circuit’s output.  Since we wanted to get to the wind tunnel, we did not take the time to figure out how to make reliable electrical connections.  Once we get that, we could also use an oscilloscope to better measure periodicity (or its inverse, frequency) and even see the wave form.


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