24 JAN 2015 by ideonexus
The Comet Loss Cone
To understand why comet showers occur, we go back to the Oort Cloud. The theory of comet showers was worked out by Jack Hills, an American physicist now at Los Alamos. He realized that the movements of the comets in the Oort Cloud are not entirely random. Comets in the cloud are generally moving in random directions, but if a comet happens to be moving in an orbit almost exactly toward the Sun, it will not survive for long. A comet in an orbit coming close to the Sun may get boiled away and d...Folksonomies: astronomy astrophysics
Folksonomies: astronomy astrophysics
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notes08 JAN 2013 by ideonexus
Science is Monism
Monism is the default worldview of natural science. In science, an explanation has to be grounded in empirical evidence. In a slightly different take, for a statement to be considered a scientific explanation, it must be falsifiable—there has to be some kind of test that could be applied to the statement to prove it wrong. For example, the statement that the moon is made of cheese is a scientific statement because it can be falsified. Facts can be brought to bear on the claim (such as the d... 1 notes
notesScientific statements must be falsifiable.
20 JUN 2012 by ideonexus
Newton on the Power of Gravity
As he sat alone in a garden, he [Isaac Newton in 1666, age 24] fell into a speculation on the power of gravity; that as this power is not found sensibly diminished at the remotest distance from the centre of the earth to which we can rise, neither at the tops of the loftiest buildings, nor even on the summits of the highest mountains, it appeared to him reasonable to conclude that this power must extend much further than was usually thought: why not as high as the moon? said he to himself; an... 1 notes
notesWondering if it extended up to the moon.
08 JUN 2012 by ideonexus
Fear of Comets
When the movement of the comets is considered and we reflect on the laws of gravity, it will be readily perceived that their approach to Earth might there cause the most woeful events, bring back the deluge, or make it perish in a deluge of fire, shatter it into small dust, or at least turn it from its orbit, drive away its Moon, or, still worse, the Earth itself outside the orbit of Saturn, and inflict upon us a winter several centuries long, which neither men nor animals would be able to be... 1 notes
notesLambert considers the gravity of the comet and how it might throw the Earth out past Saturn.
08 FEB 2012 by ideonexus
The Earliest Account of Newton and the Apple
In the year 1666 he retired again from Cambridge... to his mother in Lincolnshire & whilst he was musing in a garden it came into his thought that the power of gravity (wch brought an apple from the tree to the ground) was not limited to a certain distance from the earth but that this power must extend much farther than was usually thought. Why not as high as the moon said he to himself & if so that must influence her motion & perhaps retain her in her orbit, whereupon he fell a c... 1 notes
notesIncludes the fact that he extended the force pulling the apple to the ground up to the moon.
11 JAN 2012 by ideonexus
Newton's Discovery of Gravity as an Example of Induction ...
All the knowledge we possess of external objects is founded upon experience, which furnishes facts; and the comparison of these facts establishes relations, from which induction, the intuitive belief that like causes will produce like effects, leads to general laws. Thus, experience teaches that bodies fall at the surface of the earth with an accelerated velocity, and with a force proportional to their masses. By comparison, Newton proved that the force which occasions the fall of bodies at t... 1 notes
notesHe extended the force pulling everything down to the Earth out to the Moon, then to the Sun, and then the planets to see how our solar system really works.
01 JAN 2012 by ideonexus
The Parallax Method
It is possible to measure how far away from us each galaxy is. How? How, for that matter, do we know how far away anything in the universe is? For nearby stars the best method uses something called 'parallax'. Hold your finger up in front of your face and look at it with your left eye closed. Now open your left eye and close your right. Keep switching eyes, and you'll notice that the apparent position of your finger hops from side to side. That is because of the difference between the viewpoi...Folksonomies: measurement parallax
Folksonomies: measurement parallax
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notesUsing the change in position of an object when viewed from two different points can be used to determine its distance from you.
01 JAN 2012 by ideonexus
Sports on Phobos
Because of their small sizes, Phobos and Deimos have very low gravitational
accelerations. Their gravities do not pull very hard. The pull on Phobos is only
about one one-thousandth of that on Earth. If you can perform a standing high
jump of two or three feet on Earth, you could perform a standing high jump of
half a mile on Phobos. It would not take many such jumps to circumnavigate
Phobos. They would be graceful, slow, arcing leaps, taking many minutes to reach
the high point of the self-p... 1 notes
notesHow the low gravity and tiny size of Mars' moon would affect the game.
19 MAY 2011 by ideonexus
The Empty Space in an Atom
A favourite analogy portrays the nucleus as a fly
in the middle of a sports stadium. The nearest neighbouring nucleus is another fly, in the middle of
an adjacent stadium. The electrons of each atom are buzzing about in orbit around their respective flies, smaller than the tiniest gnats, too small to be seen on the same scale as the flies. When we
look at a solid lump of iron or rock, we are 'really' looking at what is almost entirely empty space. It
looks and feels solid and opaque because o...
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1 Our senses are not adapted to experience the empty space between atoms.
12 MAR 2011 by ideonexus
What If People Stopped Valuing Money?
Mexico and Chile and Brazil and Argentina were likewise bankrupt--and Indonesia and the Philippines and Pakistan and India and Thailand and Italy and Ireland and Belgium and Turkey. Whole nations were suddenly in the same situation as the San Mateo, unable to buy with their paper money and coins, or their written promises to pay later, even the barest essentials. Persons with anything life sustaining to sell, fellow citizenes as well as foreigners, were refusing to exchange their goods for mo...Vonnegut describes a fictional account of the currencies of numerous countries in the world suddenly being no longer valuable, making them just pretty paper.
