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
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.
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