1. Gravity: The gravitational pull between the Sun and each planet is the primary force responsible for keeping planets in their orbits. The Sun's massive size creates a strong gravitational field that pulls the planets towards it.
2. Inertia: Planets are constantly moving, and this motion creates inertia. Inertia is the tendency of an object to resist changes in its motion. The inertia of a planet keeps it moving forward in a straight line.
How these factors work together:
* Gravity is pulling the planet towards the Sun, trying to make it fall in.
* Inertia is trying to make the planet continue in a straight line, away from the Sun.
The combined effect of these two forces results in the planet following a curved path – an ellipse – around the Sun.
Think of it like swinging a ball on a string: the string represents gravity pulling the ball towards your hand (the Sun), while the ball's inertia keeps it moving in a circle.
