How do spaceships move in space without any propulsion source?

  • Context: High School 
  • Thread starter Thread starter MotoH
  • Start date Start date
  • Tags Tags
    Space
Click For Summary

Discussion Overview

The discussion revolves around the mechanics of how spaceships move in the vacuum of space without a traditional propulsion source. Participants explore concepts related to Newton's laws of motion, particularly focusing on action and reaction forces, and the implications of the center of mass in a system. The conversation includes both theoretical explanations and practical examples.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how a spaceship can move in space if there is nothing to push against, indicating a fundamental curiosity about propulsion in a vacuum.
  • Another participant illustrates the concept of action and reaction using a skateboard analogy, suggesting that pushing off another object results in movement.
  • Some participants affirm that Newton's Third Law applies in space, noting that a spacecraft pushes against the propellant it ejects to generate movement.
  • There is a suggestion that any object ejected from the spacecraft can create movement in the opposite direction, which some find easy to understand.
  • One participant introduces the idea of the center of mass, explaining that throwing a mass from the rocket causes the rocket to move in the opposite direction to maintain the center of mass.
  • Another participant presents an alternative propulsion method involving external forces, such as using solar sails or lasers, to propel a spacecraft.

Areas of Agreement / Disagreement

Participants generally agree on the application of Newton's Third Law in the context of space travel, but there are differing views on the acceptance of these concepts by the general public and the potential for alternative propulsion methods.

Contextual Notes

Some participants express uncertainty about the general understanding of these principles, indicating that misconceptions may exist regarding propulsion in a vacuum. The discussion also touches on the complexity of the center of mass concept and its implications for movement.

MotoH
Messages
53
Reaction score
2
This seems like a very fundamental question, but I have always wondered it. (please move to another section if this is in the wrong place!)

How does a spaceship move in space? If there is nothing for a rocket to push against, how does it move?

Any forms of literature would be excellent on this subject, as I am not really sure what to google for information!

Thanks!

MotoH
 
Astronomy news on Phys.org
Stand on a skate board next to a friend on another skate board, have the wheels all pointing in the same direction along the line joining you both. Now push your friend and see what happens...

Garth
 
So there is an equal and opposite reaction in space? I thought space was a vacuum therefor no molecules to push against in order to go forward?
 
Newton's Third Law: For every action there is an equal and opposite reaction.

In space, a vehicle would actually be pushing against the propellant it is ejecting.
 
Oh! So anything can be pushed out of the vehicle, and it will "push" the spacecraft in the opposite direction.

Very easy to understand now! Thanks!
 
Better example, stand on the skateboard and throw a brick. (If I did this I would land on my backside, so the assumption is you are a competent skateboarder!)
 
MotoH said:
Oh! So anything can be pushed out of the vehicle, and it will "push" the spacecraft in the opposite direction.

Very easy to understand now! Thanks!

Unfortunately a lot of people can't accept the fact that throwing stuff out of a rocket very fast is the only way it will move.
 
Another way to think about this is the "center of mass". As long as there is no external force, the center of mass of a system remains motionless. if you throw a small mass out of your rocket ship, it is still considered part of the system. In order that the center of mass remain in the same place, the rest of the rocket ship must move in the opposite direction.

Of course, the center of mass of a two-piece system, of greatly different masses, will remain "near" the greater mass. That's why we have throw that small mass (the reaction gasses in the rocket's jet) very, very fast- much faster than we want the rocket to travel.
 
qraal said:
Unfortunately a lot of people can't accept the fact that throwing stuff out of a rocket very fast is the only way it will move.

Actually, there is another way: throw stuff (from the "outside") at the rocket. That's how a solar sail works. Some people have even suggested using earth-based (or maybe moon-based) lasers to propel a spacecraft equipped with a sail.
 

Similar threads

  • · Replies 25 ·
Replies
25
Views
3K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 18 ·
Replies
18
Views
2K
  • · Replies 12 ·
Replies
12
Views
6K
  • · Replies 17 ·
Replies
17
Views
5K
  • · Replies 22 ·
Replies
22
Views
4K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 17 ·
Replies
17
Views
4K
  • · Replies 24 ·
Replies
24
Views
5K