What are Kepler's three laws of motion?

Answer 1

Basically, The amount of time it takes a planet to make one complete orbit around the sun, squared, has a common ratio to it's semi major axes, cubed. It's a little confusing. Watch this video on YouTube, it explains all of his laws very well.

http://www.youtube.com/watch?v=7mKcnfMhukU

Answer 2

Planets orbit in ellipses with the Sun at one focus.

The line from the sun to any planet sweeps out equal areas in equal times.

The square of the orbital period of the planet is proportional to the cube of the semi-major axis of its orbit.

Answer 3

Kepler's laws are about the planets' orbits.

The first law says that the orbit of any planet around the Sun is an ellipse with the Sun at one of the focii.

The second law states that the line joining the Sun to a planet covers equal area in equal intervals of time.

The third law states the square of the time period of the planet is proportional to the cube of the semi-major axis of its elliptical orbit.

Kepler's law explained planetary motion, but nothing other than motion, and really no one could properly explain why Kepler's law worked. So therefore we move on to Newton's first law.

Answer 4

First: All planets travel in elliptical orbits with the Sun at one focus

Second: If a line is drawn from the Sun to a planet, the area that the line sweeps across is equal for different distances at equal times

Third: The distance of a planet from the Sun is related to the speed of the planet

Answer 5

Kepler's Laws of Planetary Motion:

1] Each planet moves in an elliptical orbit with the sun at one focus

2] The line form the sun to any planet sweeps out equal areas of space in equal time intervals

3] The squares of the times of revolution (days, months or years) of the planets are proportional to the cubes of their average distances from the sun.

Answer 6

That more distant planets orbit the sun at slower average speeds obeying a precise mathematical relationship, p^2 (P squared) = a^3 ("a" cubed).

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Very nice. Now let's try to answer the question.

In this presentation of Kepler's 3rd law,

-- ' p ' is the orbital period of something that's gravitationally bound to the sun ...

a planet, an asteroid, a comet, etc.

-- ' a ' is a fundamental dimension of the orbit. For a circular orbit it's the constant

distance from the sun; for an elliptical orbit it's half the length of the ellipse.

This amazing simple equation from Kepler tells you everything you always

wanted to know about the relationship between the size of the orbit and the

time it takes the body to complete one revolution.

It says that for the same central body, the number you get when you divide

(square of the orbital period) by (cube of the radius or semi-major-axis) is

always the same number! We know what the number is for the sun, because

we know 'p' and 'a' for the Earth, and Kepler's law says that it's the same

number for anything else that orbits the sun. If we put a spacecraft in a

particular orbit around the sun, this tells us exactly how long it'll taker to revolve

in that orbit. Or, the other way around, if we want to put up a spacecraft that

takes 249.7846 days to orbit the sun, this simple equation tells us what the

dimensions of the orbit have to be.

Does it work for other central bodies besides the sun ? It sure does. If we look

at the orbits of Sputnik-I, Laika the dog, Yuri Gagarin, John Glenn, the Hubble

Space Telescope, the International Space Station, a geosynchronous TV satellite,

and the moon, guess what! (Period squared) divided by (orbital distance cubed)

is the same number for every one of them. Because they're in orbit around the

same central body ... the Earth. If we want to put up a TV satellite that takes

exactly 24 hours to orbit the Earth, Kepler's law tells us exactly how high the

satellite has to be. That's why all the TV satellites are in the same orbit.

Answer 7

P2 / A3 = a constant

-- ' p ' is the orbital period of something that's gravitationally bound to the sun ...

a planet, an asteroid, a comet, etc.

-- ' A ' is a fundamental dimension of the orbit. For a circular orbit it's the constant

distance from the sun; for an elliptical orbit it's half the length of the ellipse.

This amazing simple equation from Kepler tells you everything you always

wanted to know about the relationship between the size of the orbit and the

time it takes the body to complete one revolution.

It says that for the same central body, the number you get when you divide

(square of the orbital period) by (cube of the radius or semi-major-axis) is

always the same number! We know what the number is for the sun, because

we know 'p' and 'a' for the Earth, and Kepler's law says that it's the same

number for anything else that orbits the sun. If we put a spacecraft in a

particular orbit around the sun, this tells us exactly how long it'll taker to revolve

in that orbit. Or, the other way around, if we want to put up a spacecraft that

takes 249.7846 days to orbit the sun, this simple equation tells us what the

dimensions of the orbit have to be.

Does it work for other central bodies besides the sun ? It sure does. If we look

at the orbits of Sputnik-I, Laika the dog, Yuri Gagarin, John Glenn, the Hubble

Space Telescope, the International Space Station, a geosynchronous TV satellite,

and the moon, guess what! (Period squared) divided by (orbital distance cubed)

is the same number for every one of them. Because they're in orbit around the

same central body ... the Earth. If we want to put up a TV satellite that takes

exactly 24 hours to orbit the Earth, Kepler's law tells us exactly how high the

satellite has to be. That's why all the TV satellites are in the same orbit.

Was Kepler a cool guy or what !

Answer 8

The first law is: Kepler discovered that Mars did not move in a circle around the sun, but moved in an elongated ellipse. An ellipse is a closed curve in which the sum of the distances from the edge of the curve to two points inside the ellipse is always the same.

The second law is: Kepler discovered that the planets seemed to move faster when they are closer to the sun and slower when they are farther away.

The third law is:Kepler noticed that planets that are more distant from the sun as Saturn, take longer to orbit the sun. This explains the relationship between the period of a planet's revolution and its semimajor axis. Knowing how long a planet takes to orbit the sun, Kepler was able to calculate the planet's distance from the sun.

Answer 9

The cubes of the average distances of the planets from the sun is proportional to the squares of their periods.

Answer 10

A planet should move at its greatest speed when it is closest to the sun.