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## The KnotPlot Site – trefoil

“Here you will find a [browsable] collection of knots and links, viewed from a (mostly) mathematical perspective. Nearly all of the images here were created with KnotPlot, a fairly elaborate program to visualize and manipulate mathematical knots in three and four dimensions.” The diagrams are in color and are exceptionally clear.

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## Lithium – Periodic Table – element 3

Lithium is a Group 1 (IA) element containing just a single valence electron (1s22s1). Group 1 elements are called "alkali metals". Lithium is a solid only about half as dense as water. A freshly cut chunk of lithium is silvery, but tarnishes in a minute or so in air to give a grey surface.

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## Kepler’s Three Laws of Planetary Motion

The laws were formulated between 1609 to 16l9, and are (as usually stated):

• Planets move around the Sun in ellipses, with the Sun at one focus
• The line connecting the Sun to a planet sweeps equal areas in equal times.
• The square of the orbital period of a planet is proportional to the cube (3rd power) of the mean distance from the Sun in (or in other words–of the"semi-major axis" of the ellipse, half the sum of smallest and greatest distance from the Sun)
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## From Stargazers to Starships

This high-school level tutorial focuses on three topics: Astronomy of the Earth's motion in space, which includes information, and some experiments and projects that teach concepts about the calendar, seasons, Kepler's laws, building a sundial, and more; Newtonian mechanics, which ha understanding Newton's laws and discussion of mass and motion; and Spaceflight and Spacecraft. Includes a timeline, a list of concepts covered, and a glossary.

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## Clock

Clocks

How long is a day?
It's the amount of time it takes for the Earth to rotate one time on its axis. But how long does it take the Earth to rotate? That is where things become completely arbitrary. The world has decided to standardize on the following increments:

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## Boolean Logic

Boolean Searching on the Internet:

Boolean logic consists of three logical operators:

• OR
• AND
• NOT
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## three-point landing

NOUN: An airplane landing in which the two main wheels and the nose wheel, tail wheel, or tailskid all touch the ground simultaneously. Continue reading three-point landing

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## Color television

Baird was an early pioneer in this area, and one of the first techniques developed employed a system whereby the normal frame frequency was increased by a factor of three, each successive frame containing the material for one primary color. Continue reading Color television

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## How small can a genome be and still remain functional?

Henry Gee investigates

Tuesday April 24, 2001 The Guardian

Once upon a time, many hundreds of millions of years ago, a few bacteria – a committee of microbes – got together to form the first eukaryote, the first cell with an organised nucleus.

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## Liquid

 one of the three commonly recognized states in which matter occurs, i.e., that state, as distinguished from solid and gas, in which a substance has a definite volume but no definite shape. 1