You have to define your goal.
A helicopter can hover by design.
Hovercraft are a group of low draft boats that basically ride on an air cushion, generally for water travel, but may be able to come up on flat land too. They vary from personal sized to large ferries.
There are now maglev trains.
There is also a flymo lawn mower.
Near ground hovering may reduce resistance, but I don't foresee general use of something hovering significantly above the ground, and over rough terrain like the Star Wars Speeders.
Physics, Astronomy & Cosmology / Re: What is the largest domino that a smaller domino can topple in a chain reaction?« Last post by cheryl j on 20/04/2014 04:25:22 »
I wondered about that too. In demonstrations with equally sized dominoes, it seems to speed up towards the end, but I didn't know if that was an illusion.
« Last post by evan_au on 20/04/2014 04:13:09 »
"Drunk Tank Pink" was proposed in psychological studies as a color that would calm aggression - some police stations started painting cells in this color - especially the cells for violent drunks - the "drunk tank".
Physics, Astronomy & Cosmology / Re: What is the largest domino that a smaller domino can topple in a chain reaction?« Last post by CliffordK on 20/04/2014 03:52:32 »
Great Video BC & RD. I might have to find a set of dominoes to play with, or perhaps makes some pseudo-dominoes.
Somebody has probably worked out all the domino equations.
The tipping point of the domino is where the center of gravity is exactly over the corner, or where the two opposite corners line up vertically. That also delineates the energy required to lift the center of mass to the tipping point.
I believe the minimum spacing for equal dominoes to sustain a chain reaction would be where the center of mass of the falling domino is at the same elevation of the center of mass of the standing domino (where it was). Is this twice the first angle to the tipping point? This would be slightly less than twice the thickness of the domino. Or, somewhere thereabouts.
Is spacing them a single domino thickness apart too close?
Of course, all the points are moving, so as the next domino topples, the previous one is still pushing slightly, so you may be able to space them closer than I had originally guessed, but still, a single domino width is probably close to the minimum.
I'm not quite sure what the optimal spacing is, and it may well be different for equal sized dominoes, and different sized dominoes.
However, there may be some acceleration of toppling of equal sized dominoes.
So, the film suggested about 1.5X for successive larger dominoes.
Now, what if one put multiples in?
AAA BBB CCC DDD E
Would one experience slight acceleration of the toppling of identical dominoes, and thus being able to topple slightly larger dominoes, perhaps 1.6 or 1.7X?
« Last post by RD on 20/04/2014 03:37:22 »
Something "platy". e.g. ...
Posting in a forum dedicated to mineralogy sounds like a better bet , e.g. ...
« Last post by federico on 20/04/2014 02:27:26 »
Hi! i'm new in this forum. I'm ten years old. I wonder if anyone could help me identify this rock. I found it in the rainforest of Misiones in Argentina. Thank you.
« Last post by cheryl j on 20/04/2014 00:08:19 »
Red might be associated with fire, with blood spilled, or the red face of your angry enemy, in which case it could be a learned association but also possibly innate. Red is also the color of a lot of positive stimuli - red berries or red lips. But I would agree it's a "play attention to me" signal.
Purple, I believe, was an expensive die from snails, so historically, you had to be rich and special to wear it, so to me that seems cultural.
Perhaps yellow became associated with cowardliness because fear tends cause pallor, or because some animals (snakes, fish, etc) have a yellow belly when they roll over on their back.
As for blue, it seems to go both ways:
Smiling at me
Nothing but blue skies
Do I see
Singing a song
Nothing but bluebirds
All day long
I do not know if this will work at all, but i was thinking that if you used infrared controlling altitude sensors and connected them to a strong propellor (or several) and then attached this to (or within) a board, would there be a possibility - if using strong enough propellors - that it would be able to hold the weight of a person.
Some toys have come out with this technology of hovering when it senses an object beneath it. Could you take this and make it into something useable as transport?
Just a theory, anyone know if this would work?
Plant Sciences, Zoology & Evolution / Re: Is evolution of human thought now more important than biological evolution?« Last post by evan_au on 19/04/2014 22:26:41 »
evolution of the human thought processes vs biological selection?
A new concept can spread around the world via the internet in hours, and be seen by a billion people within a week (and be forgotten just as quickly). It takes longer if it has to cross language and cultural barriers.
With jet flight, a new gene can move to the other side of the world in 24 hours - but it takes 9 months to affect 1 life, and probably hundreds of years to affect a million people (millions of today's Chinese have Ghengis Khan as their ancestor).
If and when GM becomes safe and effective for humans, it will be possible for a new gene to spread at the speed of the internet - but until we can emulate the functioning of the whole genome on a computer, it will take decades to prove that a particular gene variant is safe for use. But we can draw on the billions of gene variants that have already been tried in the human population by the traditional methods.
How far off is 'direct thought communication technology'?
There has been significant progress in moving from the ability to control a cursor on the screen, cochlear implants, being able to control a robotic arm, experimental artificial retina, and working towards a brain-controlled robotic suit.
Much of this brain-machine communication relies on the physical relationship between certain nerves and the outside world. Even then, it requires both learning from the machine and retraining of the brain to achieve a useful result, and the electrical contacts are short-lived.
High-level concepts such as "cup" and "love" do not have a physical representation in accessible nerve cells, and the representation may well differ dramatically between individuals, so turning these concepts into communication to a machine, to be forwarded to another brain is still some way away.
we would be living as efficient 'brains in jars'
Physical brains are awash in chemicals generated by distant parts of the body. Some of these chemical messengers are excluded by the blood-brain barrier, but others provide important signaling to and from the body. It is not clear how well the brain would function without these, and whether they could be simulated by machines.
Emulating a biological brain inside a computer (as imagined in the movie "Transcendence") is likely to consume hundreds of Megawatts using current technology, much larger than the roughly 20-25 Watts that is consumed by our biological brains.
The power consumption of computers typically halves every 18 months - and bigger jumps are possible by allowing increased uncertainty in the processing - but it is far from being "efficient".
Where can I post maths related thread(s) in this forum?
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