Magnetic Posted August 8, 2006 Report Share Posted August 8, 2006 Hi All, Admin's, Mod's, Members. I have joined up but to ask one question or to get directed to the right place to ask it..... Newton's Cradle- how can I make one that runs for a long time. I am imagining that by using magnets and an electromagnet I shouldbe able to make it run longer, along the lines of those rotating mobiles(usually featuring a dolphin) that swing around and around. Now can I get away with a fixed magnet and a permanent electromagnet or do I need a switching arrangement turning the electromagnet off and on? Any ideas? Regards. Quote Link to comment Share on other sites More sharing options...
Jay-qu Posted August 8, 2006 Report Share Posted August 8, 2006 It will have to be switched on and off or reversed polarity because otherwise it will probably mess up the swinging (harmonic motion). So this means it would have to be an electro-magnet. I would place it at the ends at a spot the balls can nearly swing up to so that when they swing they will be drawn outwards a little higher in the swing, at this point the magnet would need to be switched off allowing the ball to fall back and collide, the same process would then occur on the other side. but you may get away with only having it on one side. Quote Link to comment Share on other sites More sharing options...
Magnetic Posted August 9, 2006 Author Report Share Posted August 9, 2006 Sounds good, and along the lines of what I have been thinking although an external electromagnet poking up at the ends of the device might spoil the asthetic appeal of the cradle. Can I get away with concealing the magnets inside the balls?...this hurts my brain to think about how it might work...attraction & repulsion competing, accurate timing and switching. Actually back to the original idea.... whats going to activate the switching of the electromagnet or conceal its appearance? ....just thinking out loud.:eek_big: Quote Link to comment Share on other sites More sharing options...
CraigD Posted August 9, 2006 Report Share Posted August 9, 2006 Now can I get away with a fixed magnet and a permanent electromagnet or do I need a switching arrangement turning the electromagnet off and on?There must be a switch. I’ve taken apart one of the “swinging dolphin” toys you mention, and discovered a simple magnetic reed switch in the base, and a small permanent magnet in the swinging part. You can buy reed switches and electromagnets for just a few dollars at most decently-stocked electronic parts stores (eg: Radio Shack), or online mail order. It would also be easy, and possible avoid some design and assembly effort, to just use the base of a “swinging dolphin” toy, as they’re fairly easy to find and inexpensive, and already have a working battery, electromagnet, and switch assembly, and a magnet small enough to put inside the ball of a Newton’s cradle, but I’m not certain that would work for what you have in mind. The main challenge I expect you’ll have is getting the balls in the middle to remain stationary while the outer balls swing. The Newton’s cradles I’ve seen quickly end up with all the balls swinging together, with none of the desired clicking collisions. You might be able to prevent this by supergluing the inner balls together, and attaching one of them to the base with thread or monofilament line, or perhaps an always-on magnet would work.Can I get away with concealing the magnets inside the balls?Yes....this hurts my brain to think about how it might work...attraction & repulsion competing, accurate timing and switching.the toys I’ve seen work just by switching the electromagnet off and on to attract the pendulum’s magnet. They don’t reverse polarity to repel it. Apparently, the delay in the reed switch is enough to assure that the pendulum gets a bit more downward force on its downswing than an its upswing, giving it enough energy with each swing to overcome friction “perpetually”. It sounds like an interesting project, with lots of tinkering required. Be sure to keep us up-to-date on you progress, and good luck! PS: The mystery perpetual motion top is my favorite of these toys. Unlike the “swinging dolphin” pendulum-type toys, these switch the electromagnet on, not off, when the magnet in the top approaches the it, giving the top a “kick” that both flings it to the outer part of base, but maintains the top’s rotation. I’m still a little mystified as to precisely how these toys work. Quote Link to comment Share on other sites More sharing options...
Turtle Posted August 9, 2006 Report Share Posted August 9, 2006 Newton's Cradle- how can I make one that runs for a long time. I am imagining that by using magnets and an electromagnet I shouldbe able to make it run longer, along the lines of those rotating mobiles(usually featuring a dolphin) that swing around and around. Question: When is a magnetic cradle not a cradle? Answer: When its a magnetically levitating Bed>:) http://news.yahoo.com/s/nm/20060807/od_nm/dutch_bed_dc Quote Link to comment Share on other sites More sharing options...
Magnetic Posted August 10, 2006 Author Report Share Posted August 10, 2006 There must be a switch.Yes.the toys I’ve seen work just by switching the electromagnet off and on to attract the pendulum’s magnet. They don’t reverse polarity to repel it. Apparently, the delay in the reed switch is enough to assure that the pendulum gets a bit more downward force on its downswing than an its upswing, giving it enough energy with each swing to overcome friction “perpetually”. Cool. So how does it work? Anyone out there got a dolphin toy to test? Is the electromagnet in the base default 'always on' only switching off when the swinging magnet gets close to let it fly on by?...and where do they put the reed switch so its not bound (or unbound) by the electromagnet? Quote Link to comment Share on other sites More sharing options...
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