Wikipedia:Reference desk/Archives/Science/2019 September 21

= September 21 =

Spring design for bouncy garden ornament
My mother's friend has some plastic dragon flies that she wants to bounce in the wind in her garden but the wind is very weak so I think the springs need to be quite weak or even not springs at all? I can't find anything at a reasonable price so I was thinking of buying some 0.2 mm stainless steel spring wire and making my own solution. My question is: does spring stiffness increase or decrease when adding more coils? Might I be better off with [no coils at all] given that the wind is going to be near non-existent and the fireflies have little surface area to catch it. The ornaments weigh about 10-20 grams so I figure the weakest spring to hold that weight should give the best motion. I can also make the spring/wire fairly long which I suppose will make it less stiff than a short length. 88.106.182.98 (talk) 19:46, 21 September 2019 (UTC)


 * (When I followed your link I briefly saw your drawing then some scam popped up saying I need to pay somebody money to fix my PC. You might want to use a safer site to post your image, like Wikipedia Commons.)


 * Now, as for the Q, can they be suspended from above ? Then you would get a pendulum motion that might provide more movement than a spring below. The longer the suspension wires or string, the slower they will move, and the longer the motion will last. Rain might also set them in motion.


 * You might also consider one of those solar-powered doohickies that makes Santa Clause dance, etc., where you would replace Santa, etc., with the the dragonflies. That would work well if you have direct sunlight there. Be sure to get one rated for outdoor use (the one in my link probably isn't), or else waterproof it yourself. You might want to take them inside for winter, or they might get destroyed by a snow shovel, boot, etc. Here's more info than you ever wanted on these toys: . He found them at a dollar store, so I suggest you do the same. At that price, they can be considered disposable. SinisterLefty (talk) 19:52, 21 September 2019 (UTC)


 * stiffness and Spring (device) will be of help. Be aware, though, that stiffness only control force/displacement. If you put two springs in parallel, the stiffness double (for a same displacement, the force is doubled). If you put one after the other, the stiffness is divided by 2 (for an equal applied force, the displacement is doubled). That is, all things being equal, more coil -> less stiff. Beware, though that the number of coil is not the only thing that matters. Strangely enough, for an helical spring, the important factor is just the length of wire. Gem fr (talk) 20:08, 21 September 2019 (UTC)
 * You can get bird scarers that consist of a kite mounted on a fibreglass pole which waves about in the breeze. You'd have to scale it down a bit though. Alansplodge (talk) 21:28, 22 September 2019 (UTC)