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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

A body travelling at a velocity of 30ms^-1 in a straight line is brought to rest by application of brakes. if it covers a distance of 100m during this period, find the retardation.
Pamilerin Reply
what is distribution of trade
Grace Reply
what's acceleration
Joshua Reply
The change in position of an object with respect to time
Mfizi
Acceleration is velocity all over time
Pamilerin
hi
Stephen
It's not It's the change of velocity relative to time
Laura
Velocity is the change of position relative to time
Laura
acceleration it is the rate of change in velocity with time
Stephen
acceleration is change in velocity per rate of time
Noara
what is ohm's law
Stephen
Ohm's law is related to resistance by which volatge is the multiplication of current and resistance ( U=RI)
Laura
how i don understand
Willam Reply
how do I access the Multiple Choice Questions? the button never works and the essay one doesn't either
Savannah Reply
How do you determine the magnitude of force
Peace Reply
mass × acceleration OR Work done ÷ distance
Seema
Which eye defect is corrected by a lens having different curvatures in two perpendicular directions?
Valentina Reply
acute astigmatism?
the difference between virtual work and virtual displacement
Noman Reply
How do you calculate uncertainties
Ancilla Reply
What is Elasticity
Salim Reply
using a micro-screw gauge,the thickness of a piece of a A4 white paper is measured to be 0.5+or-0.05 mm. If the length of the A4 paper is 26+or-0.2 cm, determine the volume of the A4 paper in: a). Cubic centimeters b). Cubic meters
Ancilla Reply
what is module
Alex Reply
why it is possible for an object(man) to stay on air without falling down?
akande Reply
its impossible, what do you mean exactly?
Ryan
Exactly
Emmanuella
it's impossible
Your
Why is it not possible to stand in air?
bikko
the air molecules are very light enough to oppose the gravitational pull of the earth on the man..... hence, freefall occurs
Arzail
because of gravitational forces
Pamilerin
this mostly occur in space
Stephen
what is physics
Joshua Reply
no life without physics ....that should tell you something
Exactly
Emmanuella
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E=MC^2
study of matter and energy and an inter-relation between them.
Minahil
that's how the mass and energy are related in stationery frame
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Kinetic energy is the energy due to montion of waves,electrons,atoms, molecule,substances an object s.
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plz anyone can tell what is meteor and why meteor fall in night? can meteor fall in the day
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meteor are the glowy (i.e. heated when the enter into our atmosphere) parts of meteoroids. now, meteoroids are the debris resulting from the collision of asteroids or comets. yes, it occurs in daytime too, but due to the daylight, we cant observe it as clearly as in night
Arzail
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Waka
wich method we use to find the potential on a grounded sphere
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Pamilerin
Physics is the science that studies everything around us from the smallest things like quarks to the biggest things like galaxies. It's simply everything.
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It talks mainly about matter with related topics such as forces energy gravity and time. It's amazing
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Alpha
Physics generally is the study of everything around us.
Steven
physics is the branch of sceince
shafiu
physics is the branch of sceince that deal with motion
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physics is the branch of sceince that deal with motion &energy
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Yilma Reply
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Emmanuella
the study of all the natural events occuring around us..... this is Physics (until those events obey the laws of physics)
Arzail
Conservation of energy😰
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Energy, it always remains there in a physical system. it can only take the form either in motion (kinetic energy) or in rest (potential energy)
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In nature organisms feed on one another in an orderly way.
Emmanuella
that describes the food chain, in which we humans are at the top
Arzail
The energy that came initially from the sun 🌞is converted into a form in which it can be stored in green plant.
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Therefore, there is conservation of energy.
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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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