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A non-satellite body fulfilling only the first two of the above criteria is classified as “dwarf planet.”

In 2006, Pluto was demoted to a ‘dwarf planet’ after scientists revised their definition of what constitutes a “true” planet.

Orbital data and kepler’s third law
Parent Satellite Average orbital radius r (km) Period T(y) r 3 / T 2 (km 3 / y 2 )
Earth Moon 3.84 × 10 5 size 12{3 "." "84" times "10" rSup { size 8{5} } } {} 0.07481 1 . 01 × 10 19 size 12{1 "." "01" times times "10" rSup { size 8{"18"} } } {}
Sun Mercury 5 . 79 × 10 7 size 12{5 "." "79" times "10" rSup { size 8{7} } } {} 0.2409 3 . 34 × 10 24 size 12{3 "." "34" times "10" rSup { size 8{"24"} } } {}
Venus 1 . 082 × 10 8 size 12{1 "." "082" times "10" rSup { size 8{8} } } {} 0.6150 3 . 35 × 10 24 size 12{3 "." "35" times "10" rSup { size 8{"24"} } } {}
Earth 1 . 496 × 10 8 size 12{1 "." "496" times "10" rSup { size 8{8} } } {} 1.000 3 . 35 × 10 24 size 12{3 "." "35" times "10" rSup { size 8{"24"} } } {}
Mars 2 . 279 × 10 8 size 12{2 "." "279" times "10" rSup { size 8{8} } } {} 1.881 3 . 35 × 10 24 size 12{3 "." "35" times "10" rSup { size 8{"24"} } } {}
Jupiter 7 . 783 × 10 8 size 12{7 "." "783" times "10" rSup { size 8{8} } } {} 11.86 3 . 35 × 10 24 size 12{3 "." "35" times "10" rSup { size 8{"24"} } } {}
Saturn 1 . 427 × 10 9 size 12{1 "." "427" times "10" rSup { size 8{9} } } {} 29.46 3 . 35 × 10 24 size 12{3 "." "35" times "10" rSup { size 8{"24"} } } {}
Neptune 4 . 497 × 10 9 size 12{4 "." "497" times "10" rSup { size 8{9} } } {} 164.8 3 . 35 × 10 24 size 12{3 "." "35" times "10" rSup { size 8{"24"} } } {}
Pluto 5 . 90 × 10 9 size 12{5 "." "90" times "10" rSup { size 8{9} } } {} 248.3 3 . 33 × 10 24 size 12{3 "." "33" times "10" rSup { size 8{"24"} } } {}
Jupiter Io 4 . 22 × 10 5 size 12{4 "." "22" times "10" rSup { size 8{5} } } {} 0.00485 (1.77 d) 3 . 19 × 10 21 size 12{3 "." "19" times "10" rSup { size 8{"21"} } } {}
Europa 6 . 71 × 10 5 size 12{6 "." "71" times "10" rSup { size 8{5} } } {} 0.00972 (3.55 d) 3 . 20 × 10 21 size 12{3 "." "20" times "10" rSup { size 8{"21"} } } {}
Ganymede 1 . 07 × 10 6 size 12{1 "." "07" times "10" rSup { size 8{6} } } {} 0.0196 (7.16 d) 3 . 19 × 10 21 size 12{3 "." "19" times "10" rSup { size 8{"21"} } } {}
Callisto 1 . 88 × 10 6 size 12{1 "." "88" times "10" rSup { size 8{6} } } {} 0.0457 (16.19 d) 3 . 20 × 10 21 size 12{3 "." "20" times "10" rSup { size 8{"21"} } } {}

The universal law of gravitation is a good example of a physical principle that is very broadly applicable. That single equation for the gravitational force describes all situations in which gravity acts. It gives a cause for a vast number of effects, such as the orbits of the planets and moons in the solar system. It epitomizes the underlying unity and simplicity of physics.

Before the discoveries of Kepler, Copernicus, Galileo, Newton, and others, the solar system was thought to revolve around Earth as shown in [link] (a). This is called the Ptolemaic view, for the Greek philosopher who lived in the second century AD. This model is characterized by a list of facts for the motions of planets with no cause and effect explanation. There tended to be a different rule for each heavenly body and a general lack of simplicity.

[link] (b) represents the modern or Copernican model. In this model, a small set of rules and a single underlying force explain not only all motions in the solar system, but all other situations involving gravity. The breadth and simplicity of the laws of physics are compelling. As our knowledge of nature has grown, the basic simplicity of its laws has become ever more evident.

In figure a the paths of the different planets are shown in the forms of dotted concentric circles with the Earth at the center with its Moon. The Sun is also shown revolving around the Earth. Each planet is labeled with its name. On the planets Mercury, Venus, Mars, Jupiter and Saturn green colored epicycles are shown. In the figure b Copernican view of planet is shown. The Sun is shown at the center of the solar system. The planets are shown moving around the Sun.
(a) The Ptolemaic model of the universe has Earth at the center with the Moon, the planets, the Sun, and the stars revolving about it in complex superpositions of circular paths. This geocentric model, which can be made progressively more accurate by adding more circles, is purely descriptive, containing no hints as to what are the causes of these motions. (b) The Copernican model has the Sun at the center of the solar system. It is fully explained by a small number of laws of physics, including Newton’s universal law of gravitation.

Section summary

  • Kepler’s laws are stated for a small mass m size 12{m} {} orbiting a larger mass M size 12{M} {} in near-isolation. Kepler’s laws of planetary motion are then as follows:

    Kepler’s first law

    The orbit of each planet about the Sun is an ellipse with the Sun at one focus.

    Kepler’s second law

    Each planet moves so that an imaginary line drawn from the Sun to the planet sweeps out equal areas in equal times.

    Kepler’s third law

    The ratio of the squares of the periods of any two planets about the Sun is equal to the ratio of the cubes of their average distances from the Sun:

    T 1  2 T 2  2 = r 1  3 r 2  3 , size 12{ { {T rSub { size 8{1} rSup { size 8{2} } } } over {T rSub { size 8{2} rSup { size 8{2} } } } } = { {r rSub { size 8{1} rSup { size 8{3} } } } over {r rSub { size 8{2} rSup { size 8{3} } } } } } {}

    where T size 12{m} {} is the period (time for one orbit) and r size 12{m} {} is the average radius of the orbit.

  • The period and radius of a satellite’s orbit about a larger body M size 12{m} {} are related by
    T 2 = 2 GM r 3 size 12{T rSup { size 8{2} } = { {4π rSup { size 8{2} } } over { ital "GM"} } r rSup { size 8{3} } } {}

    or

    r 3 T 2 = G 2 M . size 12{ { {r rSup { size 8{3} } } over {T rSup { size 8{2} } } } = { {G} over {4π rSup { size 8{2} } } } M} {}

Questions & Answers

Water is flowing in a pipe with a varying cross-sectional area, and at all points the water completely fills the pipe. At point 1 the cross-sectional area of the pipe is 0.077 m2, and the magnitude of the fluid velocity is 3.50 m/s. (a) What is the fluid speed at points in the pipe where the cross
fagbeji Reply
what's the period of velocity 4cm/s at displacement 10cm
Andrew Reply
What is physics
LordRalph Reply
the branch of science concerned with the nature and properties of matter and energy. The subject matter of physics includes mechanics, heat, light and other radiation, sound, electricity, magnetism, and the structure of atoms.
Aluko
and the word of matter is anything that have mass and occupied space
Aluko
what is phyices
Aurang Reply
Whats the formula
Okiri Reply
1/v+1/u=1/f
Aluko
what aspect of black body spectrum forced plank to purpose quantization of energy level in its atoms and molicules
Shoaib Reply
a man has created by who?
Angel Reply
What type of experimental evidence indicates that light is a wave
Edeh Reply
double slit experiment
Eric
The S. L. Unit of sound energy is
Chukwuemeka Reply
what's the conversation like?
ENOBONG Reply
some sort of blatherring or mambo jambo you may say
muhammad
I still don't understand what this group is all about oo
ENOBONG
no
uchenna
ufff....this associated with physics ..so u can ask questions related to all topics of physics..
muhammad
what is sound?
Bella
what is upthrust
Mercy Reply
what is upthrust
Olisa
Up thrust is a force
Samuel
upthrust is a upward force that acts vertical in the ground surface.
Rodney
yes rodney's answer z correct
Paul
what is centre of gravity?
Paul
you think the human body could produce such Force
Anthony
what is wave
Bryan Reply
mirobiology
Angel
what is specific latent heat
Omosebi Reply
the total amount of heat energy required to change the physical state of a unit mass of matter without a corresponding change in temperature.
fitzgerald
is there any difference between specific heat and heat capacity.....
muhammad
what wave
Bryan
why medical physics even.we have a specoal branch of science biology for this.
Sahrrr Reply
what is physics
AbleGod Reply

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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