How Kepler derived that T^2 is proportional to r^3

In summary, Kepler did not directly prove that the period squared is proportional to the radius cubed. Instead, he used experimental data to find a relationship between these quantities. Newton's law later supported this relationship.
  • #1
parsa418
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How did Kepler exactly prove that the period squared is proportional to the radius cubed? If he didn't prove it. Then how is it proven?
 
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  • #3
Mapes said:

Kepler did not derive any of his laws from the law of gravity.
He found it by experiment, using the observation data of the planetary motions to find the relative distances and the periods of the orbital motions and then looking for a relationship between these quantities.
Newton's law came later and it was supported by the fact that it can explain the laws that Kepler found by "experiment".
 
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1. How did Kepler discover the relationship between T^2 and r^3?

Kepler discovered the relationship between T^2 and r^3 while studying the orbit of Mars. He noticed that the ratio of a planet's orbital period (T) to its average distance from the sun (r) cubed was constant for all planets in our solar system.

2. What does T^2 being proportional to r^3 mean?

This relationship means that as the distance of a planet from the sun increases, its orbital period will also increase, but not at a linear rate. Instead, the orbital period will increase exponentially as the distance increases.

3. How did Kepler prove that T^2 is proportional to r^3?

To prove this relationship, Kepler used data from Tycho Brahe's observations of the planets' positions and calculated their orbital periods and distances from the sun. He then plotted a graph of T^2 against r^3 and found that it formed a straight line, providing evidence for the relationship.

4. Why is Kepler's discovery important?

Kepler's discovery of the relationship between T^2 and r^3 was crucial in the development of modern astronomy. It helped to disprove the widely accepted belief that planets moved in circular orbits, and instead, provided evidence for elliptical orbits. It also laid the foundation for Newton's law of universal gravitation.

5. How is Kepler's discovery used in modern science?

Kepler's discovery is still used in modern science to calculate the orbital periods and distances of planets, moons, and other celestial bodies. It also plays a crucial role in the search for exoplanets, as scientists can use this relationship to estimate the size and distance of planets orbiting other stars.

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