* Law of Universal Gravitation: This law states that every particle in the Universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This means the force of gravity between a planet and its star is strongest when the planet is closest to the star and weakest when it's furthest away.
* Conservation of Energy: A planet's orbit is the result of a balance between its kinetic energy (energy of motion) and its potential energy (energy due to its position in the gravitational field). As the planet moves closer to the star, its gravitational potential energy decreases, but its kinetic energy increases, making it move faster. Conversely, as the planet moves further away, its potential energy increases, and its kinetic energy decreases, causing it to slow down.
The combination of these two factors results in an elliptical orbit:
1. Closest Point (Perihelion): When a planet is closest to its star (perihelion), the gravitational force is strongest, causing the planet to speed up.
2. Farthest Point (Aphelion): When a planet is farthest from its star (aphelion), the gravitational force is weakest, causing the planet to slow down.
3. The Path: Since the planet's speed changes as it orbits, its path is not a circle, but rather an ellipse.
Sammanfattningsvis: The elliptical shape of planetary orbits is a natural consequence of the force of gravity and the conservation of energy. The planet's speed is not constant, causing it to travel in a slightly elongated path, forming an ellipse.
