TIL that it takes less energy to launch something out of the solar system than directly into the sun. Apparently its because the massive gravity of the Sun causes objects to orbit instead of pulling objects into itself. Why?
In: Physics
Here is a longer, but hopefully more ELI5 understandable way that teaches you a bit of the whys:
You’ve read from other answers by now that the primary reason is because the Earth is already going so fast. But why can’t you just accelerate towards the sun and hit it anyway? Because of the dynamics of circular motion.
[Image for visualisation](https://www.amesweb.info/Physics/images/Uniform-Circular-Motion-Calculator.jpg)
Imagine, if you will, our classic example – a bucket of water, on a string. As you swirl it around in a circle, you can intuitively realize that to keep it going in a circle at the same speed, you have to constantly exert a pull on the string straight towards you. So even though the bucket is always moving perpendicular to you (following the v in our image), you always pull towards the centre of the circle (the a in our image).
Orbiting objects work the exact same way. To keep something on the same circle at the same speed, you need to exert a constant pull towards the centre of the circle. Luckily, we have just such a thing – the sun’s gravity! It keeps us in a constant orbit.
So now, think again of your bucket. If you pull on the string a bit harder, what happens? Your bucket won’t hit you in the face – it just starts spinning faster. Similarly, in Earth’s orbit (igoring the issue of how it will deform our orbit), you can’t get to the sun by pushing inward – because you’re in a circular motion, in the general sense, pushing yourself towards the middle harder won’t get you much closer, and instead just speed you up. It’s a bit more delicate than that, because we don’t have a fixed-length string, so our orbit can deform, but for ELI5 purposes it will do.
So assuming the suns gravity remains more or less constant (gravity decays surprisingly little over distances such as that between the Earth and the Sun), how do we get closer to the sun? We have to decelerate. By slowing how fast we’re going on the circle, gravity becomes ‘stronger’ than the speed that’s keeping us on the circle. It will pull us closer towards the sun – accelerating us again in the process – until we’re going so fast again that we’re going fast enough again to match the gravity. Again – an orbital scale this works slightly differently and ovalizes your orbit, but ELI5.
That’s why the fact Earth is already going really fast matters – because you can’t just push yourself towards the centre. Counterintuitively, you need to push yourself *backwards*, against the direction you’re going (so opposite the v in our image), to get close to the centre. Push yourself forwards – accelerate – and you’ll get farther from the centre, eventually having enough energy to just fly away. And the amount of energy you need to do that just happens to be smaller than the amount of energy you need to stop and fall into the sun.
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