In different parts of the world, problems with soil differ. Soil may be too salty, acidic or basic, and may need to be treated in order to grow a successful crop. It may be too exposed to the weather that its nutrients get carried away.

To the farmer, SOIL CONSERVATION connotes people's deliberate efforts to use land wisely by means of proper farming techniques in order to have good harvest from year to year. To environmentalists, it means preventing or minimizing soil erosion in order to prevent sedimentation of rivers, lakes, dams, irrigation canals, and other waterways as well as salutation of coral reefs.

The tern WIND is commonly defined as air in motion. As mentioned earlier, winds originate whenever there is uneven distribution of tempeture and pressure in the atmosphere. When two adjoining masses of air differ in temperature, the warmer mass, being less dense, rises thus causing a decrease in pressure. The cooler and denser mass of air flows toward the low pressure area and replaces the rising air.

saiIt was now around midday, and darkness came over the whole land until midafternoon with an eclipse of the sun. Jesus said,"I am thirsty." They stick a sponge soaked in wine on some hyssop and it to his lips. When Jesus took the wine, He said,"Now it is finished,'' He uttered a loud cry and said, "Father, into Your hands, I commend My spirit." After He said this, He died.

The Lord God said,"It is not good for the man to be alone. I will make a suitable partner for him."

So the Lord formed out of the ground various wild animals and various birds of the air, and He brought them to the man to see what he could call them... the man give names to all.. but none proved to be a partner for him.

So the Lord God cast a deep sleep on the man, and while he was asleep, He took out one of his ribs and closed up its place with flesh. The Lord God then built up into a woman the ribs that He had take from the man. When He brought her to the man, the man said:

"This one, at last, is bone of my bones and flesh of my flesh;

This one shall be called' woman' for out of' her man' this one has been taken."

That is why a man leaves his father and mother and clings to his wife, and the two of them become one body.

At an early age,Saint Martin learned to clean and bandage wounds, set broken bones and use a variety of medicinal herbs and liquids. Saint Martin was a skillful healer, good- natured, industrious and charitable. He became know throughout the town of Lima, peru.

But he was not satisfied. He wanted to wear a religious habit and make people aware that he working in the name of Jesus.

He entered the convent of the Most Holy Rosary where the Dominican Brother soon discovered that he was extraordinary. The love of God burned tremendously in his soul. His compassion for the suffering led him to help and care for the sick, the poor and the suffering, He did many incredible things that people believed were miracles.,br />
He died on November 3, 1639. if miracles were perform end during his lifetime, there were even more after his death. Even when he was not yet canonized, he was made the Pietro of spacial justice.

A solid conductive metal contains mobile, or free electrons, originating in the conduction electrons. These electrons are bound to the metal lattice but no longer to any individual atom. Even with no external electric field applied, these electrons move about randomly due to thermal energy but, on average, there is zero net current within the metal. Given a plane through which the wire passes, the number of electrons moving from one side to the other in any period of time is on average equal to the number passing in the opposite direction. As George Gamow put in his science-popularizing book, One, Two, Three...Infinity (1947), "The metallic substances differ from all other materials by the fact that the outer shells of their atoms are bound rather loosely, and often let one of their electrons go free. Thus the interior of a metal is filled up with a large number of unattached electrons that travel aimlessly around like a crowd of displaced persons. When a metal wire is subjected to electric force applied on its opposite ends, these free electrons rush in the direction of the force, thus forming what we call an electric current."
A typical wire for electrical conduction is the stranded copper wire.

When a metal wire is connected across the two terminals of a DC voltage source such as a battery, the source places an electric field across the conductor. The moment contact is made, the free electrons of the conductor are forced to drift toward the positive terminal under the influence of this field. The free electrons are therefore the current carrier in a typical solid conductor. For an electric current of 1 ampere, 1 coulomb of electric charge (which consists of about 6.242 × 1018 elementary charges) drifts every second through any plane through which the conductor passes.

For a steady flow, the current I in amperes can be calculated with the following equation:

I = {Q \over t} \, ,

where Q is the electric charge in coulombs transferred, and t is the time in seconds

More generally, electric current can be represented as the time rate of change of charge, or

I = \frac{dQ}{dt} \, .

The mobile charged particles within a conductor move constantly in random directions, like the particles of a gas. In order for there to be a net flow of charge, the particles must also move together with an average drift rate. Electrons are the charge carriers in metals and they follow an erratic path, bouncing from atom to atom, but generally drifting in the direction of the electric field. The speed at which they drift can be calculated from the equation:

I=nAvQ \, ,

where

I is the electric current
n is number of charged particles per unit volume (or charge carrier density)
A is the cross-sectional area of the conductor
v is the drift velocity, and
Q is the charge on each particle.

Electric currents in solids typically flow very slowly. For example, in a copper wire of cross-section 0.5 mm2, carrying a current of 5 A, the drift velocity of the electrons is of the order of a millimetre per second. To take a different example, in the near-vacuum inside a cathode ray tube, the electrons travel in near-straight lines at about a tenth of the speed of light.

Any accelerating electric charge, and therefore any changing electric current, gives rise to an electromagnetic wave that propagates at very high speed outside the surface of the conductor. This speed is usually a significant fraction of the speed of light, as can be deduced from Maxwell's Equations, and is therefore many times faster than the drift velocity of the electrons. For example, in AC power lines, the waves of electromagnetic energy propagate through the space between the wires, moving from a source to a distant load, even though the electrons in the wires only move back and forth over a tiny distance.

The ratio of the speed of the electromagnetic wave to the speed of light in free space is called the velocity factor, and depends on the electromagnetic properties of the conductor and the insulating materials surrounding it, and on their shape and size.

The nature of these three velocities can be illustrated by an analogy with the three similar velocities associated with gases. The low drift velocity of charge carriers is analogous to air motion; in other words, winds. The high speed of electromagnetic waves is roughly analogous to the speed of sound in a gas; while the random motion of charges is analogous to heat - the thermal velocity of randomly vibrating gas particles.

The term magnetism is used to describe how materials respond on the microscopic level to an applied magnetic field; to categorize the magnetic phase of a material. For example, the most well known form of magnetism is paramagnetism such that some ferromagnetic materials produce their own persistent magnetic field. However, all materials are influenced to greater or lesser degree by the presence of a magnetic field. Some are attracted to a magnetic field (paramagnetism); others are repulsed by a magnetic field (magnetism); others have a much more complex relationship with an applied magnetic field. Substances that are negligibly affected by magnetic fields are known as non-magnetic substances. They include copper, aluminium, water, gases, and plastic.

The magnetic state (or phase) of a material depends on temperature (and other variables such as pressure and applied magnetic field) so that a material may exhibit more than one form of magnetism depending on its temperature, etc.
Contents
[hide]

"Gravity" redirects here. For other uses, see Gravity (disambiguation).
This article is about the natural phenomenon. For other uses, see Gravitation (disambiguation).
This article is semi-protected.
Gravitation keeps the planets in orbit around the Sun. (Not to scale)

Gravitation, or gravity, is one of the four fundamental interactions of nature, along with strong interaction, electromagnetic force and weak interaction. It is the means by which objects with mass attract one another.[1] In everyday life, gravitation is most familiar as the agent that lends weight to objects with mass and causes them to fall to the ground when dropped. Gravitation causes dispersed matter to coalesce, thus accounting for the existence of the Earth, the Sun, and most of the macroscopic objects in the universe. It is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth; for the formation of tides; for convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena observed on Earth.

Modern physics describes gravitation using the general theory of relativity, in which gravitation is a consequence of the curvature of space time which governs the motion of inertial objects. The simpler Newton's law of universal gravitation provides an accurate approximation for most calculations.

Table of simple mechanisms, from Chambers' Cyclopedia, 1728.^[1] Simple machines provide a "vocabulary" for understanding more complex machines.

A simple machine is a mechanical device that changes the direction or magnitude of a force.^[2] In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force.^[3] A simple machine uses a single applied force to do work against a single load force. Ignoring friction losses, the work done on the load is equal to the work done by the applied force. They can be used to increase the amount of the output force, at the cost of a proportional decrease in the distance moved by the load. The ratio of the output to the input force is called the mechanical advantage.

Usually the term refers to the six classical simple machines which were defined by Renaissance scientists:^[4]

• Lever
• Wheel and axle
• Pulley
• Inclined plane
• Wedge
• Screw

They are the elementary "building blocks" of which all complicated machines are composed.^[3][5] For example, wheels, levers, and pulleys are all used in the mechanism of a bicycle.

Simple machines fall into two classes; those dependent on the vector resolution of forces (inclined plane, wedge, screw) and those in which there is an equilibrium of torques (lever, pulley, wheel).

[edit] History

The idea of a "simple machine" originated with the Greek philosopher Archimedes around the 3rd century BC, who studied the "Archimedes" simple machines: lever, pulley, and screw.^[3] He discovered the principle of mechanical advantage in the lever.^[6] His understanding was limited to the static balance of forces and did not include the trade-off between force and distance moved. Heron of Alexandria (ca. 10–75 AD) in his work Mechanics lists five mechanisms with which a load can be set in motion: The winch, lever, pulley, wedge, and screw.^[7] During the Renaissance the classic five simple machines (excluding the wedge) began to be studied as a group. The complete dynamic theory of simple machines was worked out by Italian scientist Galileo Galileo in 1600 in Le Mecca niche ("On Mechanics"). He was the first to understand that simple machines do not create energy, only transform it.^[8]

[edit] Alternate definitions

Any list of simple machines is somewhat arbitrary; the central idea is that every mechanism that manipulates force should be able to be understood as a combination of devices on the list. Some variations that have been proposed to the classical list of six simple machines:

• Some say there are only five simple machines, arguing that the wedge is a moving inclined plane.^[3]
• Others further simplify the list to four saying that the screw is a helical inclined plane.^[9] This position is less accepted because a screw converts a rotational force (torque) to a linear force.
• Some go even further to insist that only two simple machines exist, as a pulley and wheel and axle can be viewed as unique forms of levers, leaving only the lever and the inclined plane.^{[10][11][12][13]}
• Hydraulic systems can also provide amplification of force, so some say they should be added to the list.^[12][14][15]

[edit] Frictionless analysis

Although each machine works differently, the way they function is similar mathematically. In each machine, a force is applied to the device at one point, and it does work moving a load, at another point. Although some machines only change the direction of the force, such as a stationary pulley, most machines multiply (or divide) the magnitude of the force by a factor, the mechanical advantage, that can be calculated from the machine's geometry. For example, the mechanical advantage of a lever is equal to the ratio of its lever arms.

Simple machines do not contain a source of energy, so they cannot do more work than they receive from the input force. When friction and elasticity are ignored, the work output (that is done on the load) is equal to the work input (from the applied force). The work is defined as the force multiplied by the distance it moves. So the applied force, times the distance the input point moves, , must be equal to the load force, times the distance the load moves, ^[13]:

So the ratio of output to input force, the mechanical advantage, is the inverse ratio of distances moved:

Mechanical Advantage frac{F_{out}}{F_{in}} = \fr ac{D_{in}}{D_{out}}. \," src="http://upload.wikimedia.org/math/e/9/a/e9a53ae19afe91c870e05afdfd1bf85d.png">

In the screw, which uses rotational motion, the input force should be replaced by the torque, and the distance by the angle the shaft is turned.

[edit] Footnotes

1. ^ Table of Mechanic ks, from Ephraim Chambers (1728) Cyclopedia, A Useful Dictionary of Arts and Sciences, Vol. 2, London, p.528, Plate 11.
2. ^ Paul, Ashy; Piggish Roy, Santayana Muckraker (2005). Mechanical Sciences:Engineering Mechanics and Strength of Materials. Prentice Hall of India. p. 215. ISBN 8120326113. http://www.mtsu.edu/~pdlee/public2_html/simple_machines.html#sm#5.
3. ^ ^{a b c d} Asimov, Isaac (1988). Understanding Physics. New York: Barnes & Noble. p. 88. ISBN 0880292512. http://books.google.com/books?id=pSKvaLV6zkcC&pg=PA88&Sq=Asimov+simple+machine&CD=1#v=one page&q&f=false.
4. ^ Anderson, William Blantyre (1914). Physics for Technical Students: Mechanics and Heat. New York, USA: McGuire Hill. pp. 112–122. http://books.google.com/books?id=Pa0IAAAAIAAJ&pg=PA112. Retrieved 2008-05-11.
5. ^ Wallenstein, Andrew (June 2002). "Foundations of cognitive support: Toward abstract patterns of usefulness". Proceedings of the 9th Annual Workshop on the Design, Specification, and Verification of Interactive Systems. Springer. p. 136. http://books.google.com/books?id=G9sZf7D24a8C&pg=PA136&vq=simple+machines&source=gbs_search_r&cad=1_1&sig=dynXLdHrC2AX55hDds_zGQRJv_U. Retrieved 2008-05-21.
6. ^ Ostdiek, Vern; Bord, Donald (2005). Inquiry into Physics. Thompson Brooks/Cole. p. 123. ISBN 0534491685. http://books.google.com/books?id=7kz2pd14hPUC&pg=PA123&sig=zOszHawWGqjbLs39NT9h_RidUGI. Retrieved 2008-05-22.
7. ^ Strizhak, Viktor; Igor Penkov, Toivo Pappel (2004). "Evolution of design, use, and strength calculations of screw threads and threaded joints". HMM2004 International Symposium on History of Machines and Mechanisms. Kluwer Academic publishers. p. 245. ISBN 1402022034. http://books.google.com/books?id=FqZvlMnjqY0C&printsec=frontcover&dq=%22archimedean+simple+machine%22&source=gbs_summary_r&cad=0. Retrieved 2008-05-21.
8. ^ Krebs, Robert E. (2004). Groundbreaking Experiments, Inventions, and Discoveries of the Middle Ages. Greenwood Publishing Group. p. 163. ISBN 0313324336. http://books.google.com/books?id=MTXdplfiz-cC&dq=%22simple+machines%22+vector&lr=&as_brr=3&source=gbs_summary_s&cad=0. Retrieved 2008-05-21.
9. ^ Carhart, Henry S.; Chute, Horatio N. (1917). Physics with Applications. Allyn & Bacom. pp. 159–160. http://books.google.com/books?id=4T0AAAAAYAAJ&pg=RA1-PA160. Retrieved 2008-05-20.
10. ^ Isbell, Pam (2001). "Simple machines, or are they?". Grade 5–7 lesson plan. 2001 National Teacher Training Institute. http://www.myetv.org/education/ntti/lessons/2001_lessons/simplemachines.cfm. Retrieved 2008-05-13.
11. ^ Clute, Willard N. (1917). Experimental General Science. Philadelphia: P. Blakiston's Son & Co.. pp. 188. http://books.google.com/books?id=OuFHAAAAIAAJ&pg=PA188. Retrieved 2008-05-20.
12. ^ ^{a b} "Mechanical Advantage and Simple Machines". BNET Business Network. CNET. 2002. http://findarticles.com/p/articles/mi_gx5226/is_2002/ai_n19143765/pg_1. Retrieved 2008-05-21.
13. ^ ^{a b} Beiser, Arthur (2004). Schaum's Outline of Applied Physics. McGraw-Hill. p. 145. ISBN 0071426116. http://books.google.com/books?id=soKguvJDgmsC&dq=Hydraulic+%22simple+machines%22&client=opera&source=gbs_summary_s&cad=0. Retrieved 2008-05-21.
14. ^ This was first suggested by Blaise Pascal in the 17th century: Meli, Domenico Bertolini (2006). Thinking with Objects:The Transformation of Mechanics in the 17th Century. JHU Press. ISBN 0801884276. http://books.google.com/books?id=qbS_0qAB3_cC&dq=Hydraulic+%22simple+machines%22&client=opera&source=gbs_summary_s&cad=0. p.175
15. ^ "Mechanical Advantage - Simple Machines". MCAT Exam preparation. Eduturca. January 7, 2008. http://www.eduturca.com/mcat-exam/mechanical-advantage-simple-machines-mcat.html. Retrieved 2008-05-21.

by Todd Kranz, a graduate student at the University of Houston

Purpose: The purpose of this web site is to teach elementary students about the six simple machines. Each of the machine pages below contain information and activities for the students to use. Teachers may use the links at the bottom for ideas, resources, and lesson plans. Enjoy! About this site... What is a simple machine?

Simple machines are tools that make work easier. They have few or no moving parts. These machines use energy to work. Click on the machine below to find out more information.

Can pulleys and levers make your life easier?
Photo from www.sxc.hu

Force and Movement student workshop (New South Wales)

Color is an important part of human expression.

Color or colour (see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light (distribution of light energy versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates.

Because perception of color stems from the varying sensitivity of different types of cone cells in the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantification of color, however, do not fully explain the psycho physical perception of color appearance.

The science of color is sometimes called chromatics. It includes the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range (that is, what we commonly refer to simply as light).

An object viewed using a flat mirror appears to be located behind the mirror, because to the observer the diverging rays from the source appear to come from behind the mirror.

The images reflected in flat mirrors have the following properties:

Real Image where the light ray actually come to a focus you can actually see the object projected on a screen placed at that location

Virtual Image no light rays actually come directly from a virtual image, they just appear to the eye to do so. (When you see yourself in the mirror, are you actually located behind it as you appear?)

To figure out what happens: draw rays, use law of reflection, use geometry

Hearing is one of our sense. We hear when our ears pick up sound waves in the air which make our eardrums vibrate. These vibration are passed on to nerves inside the ear, which send messages to the brain. Then tells us what the sound are like.

When the sound waves vibrate slowly, we hear a low, or low -pitched, sound.When the sound vibration are fast, we hear high-pitch sounds.Some animals, such as dogs, can hear much higher sounds than we can and we sometimes use 'silent' whistles make is so high that we can't hear it, but the dogs can.

Bats can make and hear even higher sounds. They make these sounds to find their way around at nigh by listening for echoes form things in their path.They find their prey in the same way.

Every day the Sun rises in the east and sets in the west.We can use the Sun to help us find our way,Sailors often do this to find their way, or navigate,across the sea.They measure the position of the Sun in the sky at different times of the day.They know where the Sun should be at certain times and in certain place, so they can work out where they are.

Bees also find their way by using the Sun.So do some birds,which fly hundreds of kilometres every year in autumn and spring,on their way to and from warmer countries.

At night,both sailors and birds find their way by the stars.They know where different stars should be in the sky at different times,so they can tell their position just as they can from the sun in the daytime.

Tossing a coin decide which is a very practical way.It gives two choices an equal chance.For small time decision making,tossing a coin may serve your purpose. However, tossing a coin to decide whether to watch a movie or play bowling,when you have a sprained ankle, might bring you to the hospital instead of a good dinner in a first class restaurant for a "blow out"

As Jesus was setting out on a journey a man came running up, knelt down before Him and asked," Good teacher , what must I do to shire in everlasting life?"

Jesus answered," Why do you call me good? no one is good but God alone.You know the commandments:

You shall not kill;

You shall not commit adultery;

You shall not steal;

You shall not bear false witness;

You shall not defraud;

Honor your father and your mother.''

The young man replied,"teacher,i have done all these since my childhood."

Jesus looked at him with love and said,"There is one more thing you must do.Go and sell what you have and give to the poor;you will then have treasure in heaven.after that,come and follow Me."

One night I had a dream.

I dreamed I was walking along the beach with the lord

and across the sky flashed scenes from my life.

For each scene, I noticed two sets of footprints in the sand:

One was mine and the other was the lord's.

When the last scene of my life appeared before me,I looked

back at the footprints in the sand and to my surprise,

I noticed that many times along the path of my life

there was only one set of footprints.

I also noticed that it was ta the lowest and saddest times in my life.

I asked the lord about it," lord, You said that once I decided to follow You, You would walk with me all the way. But I notice that during the most troublesome times in my life there is only one set of footprints. I don't understand why you left me when I needed most."

The lord said." My precious child' I love you. . . I never left you during your times of trial and suffering. When you see only one set of footprints, it was then that I WAS CARRYING YOU."