# B Mass in deep space

1. May 26, 2016

### ponyboy3399

I get so confused how mass works in space. I know these may sound like stupid questions but I've never had anyone answer them before. First if you're flying a spacecraft around in space. What role does mass play if you're weightles?
For example why couldn't you hit the gas and indefinitely accelerate to however fast you wanted to go?
I guess another question is in space what forces act on mass if there is no friction wind resistance or gravity? Is there a good link to a website that explores these questions?

2. May 26, 2016

### Mech_Engineer

Regardless of whether a spacecraft (or any object) is in a gravity field, it is subject to inertia which is in turn a primary manifestation of mass. It is inertia which prevents infinite acceleration, not gravity. See here:

https://en.wikipedia.org/wiki/Inertia

3. May 26, 2016

### PeroK

Mass is the amount of something. Mass is the same wherever something is. Weight is the force exerted on an object by a gravitational field. In everyday speech we tend to mix these up: I weigh 90kgs. That really means my mass is about 90kgs and the force exerted on me by the Earth is about 873N. If I were on the moon, my mass would be the same, but my weight would be about 1/6th of that on Earth. And, if I were in space, distant from any gravitational source, the my mass would still be 90kgs, but I would be weightless.

Newton's second law states that $F = ma$ (force = mass x acceleration). This applies everywhere, including in space. The acceleration depends on the mass: the more massive something is, the more force is required to accelerate it at a given rate.

But, out in space, there is no obvious means of causing motion. Hitting the gas in a car or opening the throttle on a jet engine would do nothing, because there is nothing to get a grip. Science fiction in this respect is very fictional: it's very difficult to engineer anything that could accelerate itself through space the way a plane can accelerate itself along the ground and in the air.

You could try googling for "spacecraft propulsion" and see what that turns up.