Help me please :)

[ComiSolja]

Can someone explain newtons law of gravity, in 9th grade words? nothing too indepth.. i just need to know what the law says..

Thanx :-)

Comi

[Cow`]

stuff falls down

[ComiSolja]

lol ok..

[XxSWATxX]

i am idiot

[XxSWATxX]

The two parts (qualitative and quantitative) of Newton's law of gravity:
Gravity is an attractive force between all pairs of massive objects in the universe.
The gravitational force between masses m1 and m2, separated by a distance r, is F = G m1 m2 / r2.

--------------------------------------------------------------------------------

(1) Gravity is an attractive force between all pairs of massive objects in the universe.
An important point is that gravity is an attractive force, tending to bring objects closer together, rather than a repulsive force. (Gravity sucks; it never spews.) Newton is referred to as creating a theory of universal mutual gravitation''. UNIVERSAL, because gravity works everywhere in the universe, not just on Earth. MUTUAL, because gravity works between pairs of objects. The gravitational force of a single object is no more real than the sound of one hand clapping.
The force of gravity, Newton realized, depends on

the MASSES of the objects involved (more massive objects feel a stronger gravitational force).
the DISTANCE between the objects involved (objects which are close together feel a stronger gravitational force).
Newton was able to express the gravitational force between a pair of objects in the form of a single equation, given in the section below.
--------------------------------------------------------------------------------

(2) The gravitational force between two objects is given by a (fairly) simple mathematical equation.
The gravitational force between a pair of objects is:
F = G m1 m2 / r2
where
F = gravitational force
m1 = mass of the first object
m2 = mass of the second object
r = distance between the centers of the objects
G = universal constant of gravitation''
The universal constant of gravitation'' G is a constant of nature; it is the same everywhere in the universe. It has been measured in laboratories, and has a value
G = 6.7 x 10-11 newton meter2/kilogram2. (Remember, the newton is the standard unit of force in the metric system; in more familiar units, 4.41 newtons = 1 pound.)
Gravitational force varies directly with the mass of each object, and inversely as the square of the distance between their centers. For instance, if you doubled the mass of the Earth, and kept its radius constant, you would double the gravitational force experienced by every object on the Earth's surface. If, on the other hand, you kept the mass of the Earth constant, and doubled its radius, the gravitational force experienced by every object on its surface would be 1/4 as large.

Double the distance between objects: Gravitational force 1/4 as large.
Triple the distance between objects: Gravitational force 1/9 as large.
Quadruple the distance between objects: Gravitational force 1/16 as large.
...and so forth...

This relationship between force and distance (F proportional to 1/r2) is known as an inverse square law''. In principle, the Earth experiences a gravitational force from every object in the universe. In practice, however, since gravitational forces decrease rapidly with distance, the Earth's gravitational acceleration is determined only by objects which are very close and/or very massive.


--------------------------------------------------------------------------------
Newton's equation for the gravitational force F can be used to compute numerical values for the force acting between objects whose mass and separation are known. As an example, let me compute the gravitational force between the Earth and the package of cookies that I brought to lecture. (Note: you will not be required to make calculations this complicated on any exam. I am just showing you this calculation to point out that it can be done!)

The equation:
F = G m1 m2 / r2
The numbers:
m1 = mass of Earth = 6.0 x 1024 kilograms
m2 = mass of cookies = 0.454 kilograms
r = radius of Earth = 6.4 x 106 meters
G = gravitational constant = 6.7 x 10-11 newton meter2 / kilogram2
The calculation:
F = (6.7 x 10-11)(6.0 x 1024)(0.454) / (6.4 x 106)2
F = 4.4 newtons
F = 1 pound.
Thus, the Earth pulls upon the cookies with a force of one pound. (We say the cookies have a weight of one pound.) Conversely, the cookies pull on the Earth with a force of one pound. Different planets in the Solar System have different masses m1 and different radii r. Thus, the weight of the package of cookies will be different on different planets, while its mass is independent of location.
If the cookies are permitted to fall freely toward the Earth, what is their gravitational acceleration?
Newton's second law of motion (see yesterday's lecture) tells us:

a = F / m2

where F is the net force on the cookies, and m2 is the mass of the cookies. But Newton's law of gravity tells us:

F = G m1 m2 / r2

If we combine the two above equations, we find that the gravitational acceleration of the cookies is:

a = G m1 / r2

Thus, the gravitational acceleration of the cookies at the Earth surface is independent of the mass. The jumbo economy family package of cookies will fall at the same rate as a miniature handy pocket pack. It depends on the mass of the Earth (m1), the radius of the Earth (r), and the gravitational constant (G), and that's it! In fact, if you plug in the numbers, you find that a = 9.8 meters/second/second at the surface of the Earth (and decreases with radius as you move upward, away from the Earth's surface). In other words, just as Galileo had observed long before Newton's birth, heavy objects and light objects at or near the surface of the Earth fall with the same gravitational acceleration.


--------------------------------------------------------------------------------
Newton wanted not only to explain the motion of falling objects near the Earth's surface, but also to explain the motion of more distant objects, such as the Moon. Let us make the simplifying assumption that the Moon is on a circular orbit. (This is a fairly good approximation, and makes the math a LOT easier.) If an object is moving on a circular orbit at a constant speed, it is being accelerated. (Even though its speed is constant, its direction of motion is continuously changing, and thus its velocity is continuously changing as well.) Since the Moon is being accelerated, it must be experiencing a force (Newton's second law of motion, again). Newton asked the question, rather daring in its audacity at the time, Could gravity be the force which is providing the Moon's acceleration, and keeping it on a circular orbit?''
It was easy for Newton to compute the speed of the Moon on its orbit. The distance to the Moon could be measured with fair accuracy in Newton's time (using a method involving parallax). In modern metric units,

radius of Moon's orbit = 3.8 x 108 meters
circumference of Moon's orbit = 2 pi times radius = 2.4 x 109 meters.
orbital period of Moon = sidereal month = 27.3 days = 2.4 x 106 seconds.
orbital speed = circumference / orbital period = 1000 meters/second
Thus, Newton was able to compute that the Moon is zipping along its orbit at a speed of 1 kilometer per second (to use modern units). Computing the acceleration of the Moon on its orbit is only a bit more difficult. It can be shown that the acceleration required to keep an object traveling on a circular orbit at a constant speed is
a = v2/r

where

v = orbital speed (1000 meters/second for the Moon)
r = orbital radius (380 million meters for the Moon).
I haven't shown the derivation for the above equation. However, if you've ever driven a car around a tight curve at a high speed, you have an intuitive grasp of the fact that the acceleration is higher (and the wheels screech louder) when the speed is high (v large) and the curve is sharp (r small).
The acceleration required to keep the Moon on its circular orbit is:

a = v2 / r = (1000 m/sec)2 / (3.8 x 108 m) = 0.0026 meters/second2

So the acceleration needed is not large. Can gravity provide the right amount of acceleration? Let's check:

Acceleration provided by gravity:

a = G m1 / r2

At the surface of the Earth, the distance r is equal to the radius of the Earth (6400 km), and the acceleration is:

a = 9.8 meters/second2

At the orbit of the Moon, the distance r is equal to 60 times the radius of the Earth (380,000 km = 60 x 6400 km, in round numbers), and so the gravitational acceleration at the Moon's orbit is decreased by a factor of 1/(60)2 relative to the gravitational acceleration at the surface of the Earth.

a = 9.8 meters/second2 / (60)2
a = 9.8 meters/second2 / 3600
a = 0.0027 meters/second2

Bottom line: The acceleration required to keep the Moon on its circular orbit is 0.0026 meters/second2, according to Newton's calculations. The acceleration provided by gravity, is 0.0027 meters/second2. The minor discrepancy between this numbers is smaller than the uncertainties in the size of the Earth and the size of the Moon's orbit as known in Newton's day. Isaac Newton was a happy man. His inverse square law for the force of gravity provided just enough acceleration to keep the Moon on its orbit.

The same force that makes apples fall from trees here on Earth is the force that keeps the Moon in its orbit, a quarter of a million miles away.

[XxSWATxX]

http://library.thinkquest.org/11902/physics/newton4.html?tqskip1=1&tqtime=0522

This is best description I found.

[ComiSolja]

Gravity is an attractive force between all pairs of massive objects in the universe.

thats exactly what i needed, thanx swat, i owe ya one

[XxSWATxX]

I was going to say that and that aloe but found alot more interesting stuff too so i posted it all.
I was even going to use my own words ;)

[ADO0MSDAY]

swat got to it before me.... but i wouldve explained it in my own words, it was last chapters material.

[XxSWATxX]

this was a few years ago for me almost 10 but i get it again soon :)

[ComiSolja]

well we learned it.. first semester.. but my book is in my locker.. :( lol

[project]

swat ur avatar is starting to irritate me.. lol..

[XxSWATxX]

does it show animation??? on my home pc it dont on my work pc it does

[Neverside]

Yes its animated

[XxSWATxX]

there i changed it happy. :( i will find a better one just gimme a day ;)

[Reg]

gravity is the stuff that when ur high, brings u back down to earth ;)

[ComiSolja]

i know what gravity is.. lol.. i didn't know what his law said about gravity :) im not THAT dumb.. geeze :P

[ComiSolja]

Thanx for everyone that helped me.. i got 150/150 on the essay thing :)