Exploring the Paradox of Thrust and Heat in a Moving Rocket Engine

  • Thread starter Stewart Snider
  • Start date
In summary, the conversation discusses the concept of a rocket engine producing heat and the effect of movement on its heat output. The question is raised about the decrease in kinetic energy of the exhaust as the engine moves and how this affects the engine's perception of movement. The answer is given that the exhaust exits with the same velocity relative to the rocket, but a lower velocity relative to the ground due to the engine's movement.
  • #1
Stewart Snider
Consider a rocket engine held stationary that produces 1000 kg of thrust.
Now, allow that engine to move on a track at, say, 100m/s, controlling its velocity with a brake, keeping the fuel burn rate the same. The brake will get hot.

But since the fuel burn rate remains the same, the rocket's heat output remains the same as well, right? All we've done is allowed the thing to move. But with movement, we're generating heat in the brake in addition to the rocket exhaust. It would seem we're getting the heat from the brake for free. This violates the law of conservation of energy, so I know there must be a flaw here.

Can anyone tell me what I'm missing?
 
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  • #2
Stewart Snider said:
Can anyone tell me what I'm missing?
The KE of the exhaust
 
  • #3
Do you mean the kinetic energy of the exhaust decreases as the engine moves? If so, I don't understand how any part of the engine knows it's moving.
 
  • #4
It doesn't need to know that it's moving. The exhaust exits with the same velocity with respect to the rocket but a lower velocity with respect to the ground because the rocket is moving.
 
  • #5
Stewart Snider said:
Do you mean the kinetic energy of the exhaust decreases as the engine moves?
Yes.

Stewart Snider said:
If so, I don't understand how any part of the engine knows it's moving.
I don't understand what you are asking here. Can you ask your question without anthropomorphising?
 
  • #6
Stewart Snider said:
Do you mean the kinetic energy of the exhaust decreases as the engine moves? If so, I don't understand how any part of the engine knows it's moving.

Ask yourself...

Does the rocket engine eject the exhaust gas at a fixed speed relative to the ground or the engine?
 

Related to Exploring the Paradox of Thrust and Heat in a Moving Rocket Engine

1. What is the paradox of thrust and heat in a moving rocket engine?

The paradox of thrust and heat in a moving rocket engine refers to the fact that as a rocket moves forward, it produces thrust to propel itself, but at the same time, it also generates a significant amount of heat due to the combustion process in the rocket engine.

2. How does the paradox of thrust and heat affect a rocket's performance?

The paradox of thrust and heat can have a significant impact on a rocket's performance. The heat generated can cause damage to the rocket's components, and the thrust produced can be affected by the heat, resulting in lower overall performance and efficiency.

3. What are some ways to mitigate the effects of the paradox of thrust and heat in a rocket engine?

To mitigate the effects of the paradox of thrust and heat, engineers can use materials that can withstand high temperatures, such as heat-resistant alloys. They can also design the rocket engine to incorporate cooling systems to dissipate the heat and prevent damage.

4. Are there any trade-offs in addressing the paradox of thrust and heat in rocket engine design?

Yes, there are trade-offs in addressing the paradox of thrust and heat in rocket engine design. For example, incorporating cooling systems adds weight to the rocket, which can affect its overall performance. Engineers must carefully balance these trade-offs to optimize the rocket's performance.

5. How does understanding the paradox of thrust and heat benefit rocket engine design?

Understanding the paradox of thrust and heat is crucial for rocket engine design because it allows engineers to develop more efficient and reliable engines. By understanding how thrust and heat are related, engineers can make informed design decisions that can improve the overall performance and safety of the rocket.

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