Okay, I’m an idiot. Just to preface this. But let’s say I’m in space. There’s no wind resistance right? If I accelerate, I’ll maintain that speed. Why can’t I just burn more fuel and go faster?
In: 194
No you are absolutely right, you can do that.
In fact that is how trips to the moon and Mars works. We use enough fuel to get a good speed going then ride on that speed until it’s time to slow down to land or enter orbit. But since you can’t bring much fuel into space, because it is sooo heavy, we can’t use too much for acceleration or we don’t have any left for slowing down and going back.
If you went in one direction out to deep space eventually you would slow down however. There actually is resistance in space, just very, very spread out. Some particles just hang around in space, even the rare air molecule. Other particles fly close to the speed of light and will hit your spaceship in the opposite direction with a lot of energy. Even starlight will eventually push your ship around.
You can. But you need to carry that fuel, so there’s far more mass to accelerate requiring even more fuel. But in theory, if you had a sufficiently efficient engine or an outside fuel supply that could supply fuel as you accelerate, you can go pretty darn fast.
Now at some point relativistic effects come into play whereby the faster you try to go, the more massive you become, requiring ever more fuel to eke out additional acceleration. But that’s not really ELI5 material.
You can, yes.
But you need to bring more fuel to do so, which means you’re heavier. Which means that you need even more fuel to burn to move at all. And that cycle just repeats–more speed = more fuel = more weight = need more fuel.
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