Why do planets have enough centripetal force to prevent themselves from crashing into the sun?


Why do planets have enough centripetal force to prevent themselves from crashing into the sun?

In: 1

That is not how centripetal force works. Centripetal force has to do with the counter force of inertia for a rotational mass pointing towards the axis of the rotation.

Planets do not crash into the sun because they are in a state of constant freefall where they are moving away from the sun as fast as they are falling into the sun so they circle around it.

Consider you throw a ball, it fly, its curve down due to gravity and hits the ground. You throw it harder, it flies farther for longer, eventually curves down and hits the ground. WHat if we threw it at say 100,000feet at 10k mph? It would fly through the air, and slowly curve down towards the Earth and land somewhere probably 5-6k miles away. Now, you go into orbit and you throw the ball with the same force that gravity is pulling it down, the ball flys forward curves down but as it curves down is still moving so fast forward is doesn’t get closer to earth anymore. Now, that ball is in orbit. It keeps moving forward an curving down but never getting any closer to the Earth.

Planets are in orbit of the sun in the same way.

If a planet is moving too slowly, it will lose altitude – it will fall towards the sun. As it falls it picks up speed, until it is moving fast enough to no longer be falling. Because of this, it is actually super hard to fall into the sun (or any planet).

This creates an oval-shaped orbit.

Over time the planets’ orbits have become balanced out and circular. Instead of having a stretched oval they are mostly circular.

The most short answer is that the matter in each solar system starts with differing amounts of energy. Matter that has low energy ends up being absorbed by the star(s) in that system. Matter with sufficient energy orbit the star(s) ends up coalescing into comets asteroids and other such bodies. Those bodies can form into planets via their gravitational pull. So the planets are essentially a combination of matter that already had enough initial energy (mostly) to orbit rather than crash into the star(s).

Anything in a stable orbit around the Sun has a perfect balance of gravity pulling it towards the Sun and a force making the motion of its orbit follow a curved path around the Sun, what’s basically centripetal force. Imagine a yo-yo you swing in a circle at the end of a string.

Anything that wasn’t in a stable orbit when the solar system was formed was eventually slingshotted out leaving only the ones with the balanced centripetal and gravitational forces. The slingshotted ones can be imagined as letting go of the string so there’s no longer a balance of forces.

There are some cool simulations of the early solar system on youtube that show it really nicely if you’re interested!

Edit: minor error and typo

The sun is a really small target. It’s just a few hundred thousand km across, whereas the solar system is billions of km across. If a planet isn’t going on just the right course to hit the sun, it’ll just keep looping around the same path, missing the sun every time.