Introduction to Kepler’s Laws
Motion is always relative. Based on the energy of the particle under motion,
motions are classified into two types:
• Bounded Motion
• Unbounded Motion
In bounded motion, the particle has negative total energy (E < 0) and has two or
more extreme points where the total energy is always equal to the potential
energy of the particle, i.e., the kinetic energy of the particle becomes zero.
For eccentricity 0 ≤ e <1, E < 0 implies the body has bounded motion. A circular
orbit has eccentricity e = 0, and an elliptical orbit has eccentricity e < 1.
In unbounded motion, the particle has positive total energy (E > 0) and has a
single extreme point where the total energy is always equal to the potential
energy of the particle, i.e., the kinetic energy of the particle becomes zero.
For eccentricity e ≥ 1, E > 0 implies the body has unbounded motion. The
parabolic orbit has eccentricity e = 1, and the hyperbolic path has eccentricity e
> 1.
Also Read:
• Gravitational Potential Energy
• Gravitational Field Intensity
Kepler’s laws of planetary motion can be stated as follows:
Kepler’s First Law – The Law of Orbits
According to Kepler’s first law, “All the planets revolve around the sun in
elliptical orbits having the sun at one of the foci”. The point at which the planet
is close to the sun is known as perihelion (about 147 million kilometres from the
sun), and the point at which the planet is farther from the sun is known as
aphelion (152 million kilometres from the sun). It is characteristic of an
ellipse that the sum of the distances of any planet from two foci is constant.
Motion is always relative. Based on the energy of the particle under motion,
motions are classified into two types:
• Bounded Motion
• Unbounded Motion
In bounded motion, the particle has negative total energy (E < 0) and has two or
more extreme points where the total energy is always equal to the potential
energy of the particle, i.e., the kinetic energy of the particle becomes zero.
For eccentricity 0 ≤ e <1, E < 0 implies the body has bounded motion. A circular
orbit has eccentricity e = 0, and an elliptical orbit has eccentricity e < 1.
In unbounded motion, the particle has positive total energy (E > 0) and has a
single extreme point where the total energy is always equal to the potential
energy of the particle, i.e., the kinetic energy of the particle becomes zero.
For eccentricity e ≥ 1, E > 0 implies the body has unbounded motion. The
parabolic orbit has eccentricity e = 1, and the hyperbolic path has eccentricity e
> 1.
Also Read:
• Gravitational Potential Energy
• Gravitational Field Intensity
Kepler’s laws of planetary motion can be stated as follows:
Kepler’s First Law – The Law of Orbits
According to Kepler’s first law, “All the planets revolve around the sun in
elliptical orbits having the sun at one of the foci”. The point at which the planet
is close to the sun is known as perihelion (about 147 million kilometres from the
sun), and the point at which the planet is farther from the sun is known as
aphelion (152 million kilometres from the sun). It is characteristic of an
ellipse that the sum of the distances of any planet from two foci is constant.
