Question: What would a space ship do if it had stopped because it ran out of fuel?

Monique Henson answered on 13 Nov 2015:

If it space ship ran out of fuel it wouldn’t immediately stop moving. On Earth a car stops moving when it runs out of fuel because of two things: friction and air resistance. Friction is the force that tries to prevent to things that are touching from moving relative to each other. When a car travels down a road, friction tries to stop the wheels from moving on the road. This means that the car loses energy as it tries to overcome this force.

Similarly, air resistance tries to stop a car moving through the air, which slows down the car. So on the Earth, these two things slow cars down, which means they need a constant supply of fuel to stay at a constant speed.

In space, there’s no atmosphere and spaceships don’t need roads – they just fly through space. This means there’s no air resistance or friction to worry about. This means that if a spaceship runs out of fuel, it will (mostly) just keep travelling at the same speed and won’t slow down.