What If You Could Build a Rocket with Infinite Exhaust Speed?

  • Context: Graduate 
  • Thread starter Thread starter peron
  • Start date Start date
Click For Summary

Discussion Overview

The discussion centers around the hypothetical scenario of constructing a rocket with exhaust particles ejected at infinite speed. Participants explore the implications of such a concept on force and motion, raising questions about the physical feasibility and the underlying principles of momentum and propulsion.

Discussion Character

  • Exploratory, Debate/contested, Conceptual clarification

Main Points Raised

  • One participant questions how a rocket could exert force if exhaust particles reach their destination instantaneously upon activation.
  • Another participant asserts that force is defined by the change in momentum and suggests that the scenario presented is impossible, rendering the exhaust velocity meaningless.
  • A different participant emphasizes that non-physical assumptions can lead to nonsensical conclusions.
  • One participant claims to have built an engine with exhaust speed equal to the speed of light (C), stating it would not move, using a flashlight as an analogy.
  • The same participant mentions the phenomenon of 'light pressure' as a real-world example of momentum change from a beam of light, suggesting it serves as a form of propulsion.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of the scenario and the implications of infinite exhaust speed. There is no consensus on the validity of the assumptions or the conclusions drawn from them.

Contextual Notes

The discussion involves assumptions about physical laws and the nature of force and momentum that may not hold in real-world physics. The implications of light pressure and its relation to propulsion are also noted but not fully resolved.

peron
Messages
15
Reaction score
0
What if you could build a rocket, with the exhaust "leaving" the engine at a instantaneous speed, would such a rocket with a infinite exhaust move?

The particles leaving the engine will reach a different destination as soon as the rocket was switched on, so how could such a rocket exert a force?

I'm kinda confused.
 
Physics news on Phys.org
Force is the change of momentum of a body. Presumably in your scenario (which is kind of impossible) the particles leaving the rocket would change the momentum of the rocket and propel it forward. Ultimately what you are describing can't happen and that makes it sort of meaningless. The velocity of the particles would be meaningless and therefore the force they exert would also be meaningless.
 
Non-physical assumptions will lead to nonsensical conclusions.
 
I built an engine that had an exhaust speed of C.
It wouldn't move at all. (turn your flashlight on...)
 
PaulS1950 said:
I built an engine that had an exhaust speed of C.
It wouldn't move at all. (turn your flashlight on...)

There is a well known phenomenon of 'light pressure'. The beam from your torch represents a steady change of momentum - so your torch is a (very feeble) propulsion unit.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
1K
Replies
27
Views
4K
  • · Replies 25 ·
Replies
25
Views
4K
  • · Replies 27 ·
Replies
27
Views
2K
  • · Replies 6 ·
Replies
6
Views
4K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 32 ·
2
Replies
32
Views
6K
Replies
1
Views
2K
Replies
6
Views
1K