# Eli5 will the earth ever run out of centrifugal force?

136 views

Like if the sun was going to exist forever (which I know it isn’t). Would the earth ever stop spinning around the sun and eventually fall into it or is ongoing?

In: 0

The Earth wouldn’t stop spinning entirely. Instead, it would eventually become tidally locked with the sun much like our moon is with Earth. Tidal forces very gradually reduce the rotational speed of an orbiting body until one side perpetually faces the larger body. So one half of the Earth would always be day and the other half always night. In this state, it rotates one time per year.

As for falling into the sun, that would take even longer as there is very little resistance to the orbital speed of a planet.

Only if a force stops it. The earth is orbiting around the sun which means its moving fast enough to avoid falling into the sun.

Imagine shooting a cannon. The ball flies for a while then falls into the earth. Lets say you put the cannon on a building and shot it. It would travel farther around the earth this time before it falls into it. Then you put it on top of a mountain. It flies even further around the earth before landing on it. So at a certain height you could assume that at the rate the earth is pulling the ball to itself is the same rate that the ball is moving therefore the cannon ball is constantly falling “towards the earth” but since it is going so fast and at such a distance above the surface, the curvature of the earth sort of gets out of the way of the ball and the ball continues to fall forever. This is orbit. Or a simplified explanation. So until a force acts on it, slows it down or changes its course, the earth will perpetually orbit the sun

no, there is nothing slowing the Earth down. If you spin a bike wheel, it will slow down due to air resistance. There is no air in space.

even if sun stops shining, it will still have its mass, which will keep the earth in orbit around it.

if sun explodes, it can push earth into a different orbit. If that explosion throws away a lot of sun’s mass, then that will change the orbit too. But earth will still retain its momentum.

The only way to slow down earth’s orbital speed is to hit it head-on with an large asteroid. Or have that large asteroid fly by closely enough to pull earth after it.

No force is being expended to keep Earth on the orbit, and centrifugal force plays no part in it. On the contrary, Earth has so much initial speed that to crash into the Sun, you would have to expend a great amount of energy to slow Earth down to have it fall in. In general, from this point, it’s easier to shoot things out of the solar system entirely than it is to shoot them into the Sun.

Centrifugal force is an illusion created by the opposing forces of inertia and gravity. Inertia makes the Earth want to fly off into space. Gravity pulls it toward the sun. The orbit of the Earth would be changed if something throws these forces out of balance. Every orbit eventually decays, as nothing is in perfect balance.

There are very small gravitational forces, and probably other things that I am forgetting, that would slow the Earth’s orbit given enough time. Losses due to gravitational waves are on the order of only a few watts though, so it would take an absurdly long time for that to happen.

Yes and no?

There are forces acting on earth, solar winds, and the combine gravitational effects of every object in our solar system (and beyond). All else being equal, we would spiral into the sun eventually.

But… the sun is losing mass through its fusion reaction. And as a result, it’s pull on the planets is decreasing, meaning earth floats about 1.5cm away from the sun every year.

This reaches a paradox to your question, as the reduction in mass cannot be indefinite even in a hypothetical world. So in a world where the sun doesn’t age, and therefore doesn’t shrink… yes we would eventually spiral into the sun.

But in reality, the opposite is happening.