How Does Weight and Thrust Affect Rocket Acceleration and Velocity?

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Discussion Overview

The discussion revolves around the effects of weight and thrust on rocket acceleration and velocity, exploring hypothetical scenarios involving different payload weights and thrust levels. It touches on concepts related to rocket physics, including thrust-to-weight ratio and the implications for reaching orbit.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether different rockets with varying weights and thrust levels would accelerate at the same rate, reach the same velocity, or achieve the same orbit.
  • Another participant asserts that rockets do not accelerate at the same rate, referencing Newton's second law (F = ma) to explain that decreasing mass while keeping force constant increases acceleration.
  • A third participant introduces the concept of thrust-to-weight ratio, emphasizing its importance in avionics and the need for it to be greater than 1 for launch. They also mention factors like heat tolerance of thrusters and structural stresses as complex engineering considerations.

Areas of Agreement / Disagreement

Participants generally agree that rockets with different weights and thrust levels will not accelerate at the same rate. However, the discussion remains unresolved regarding the broader implications for velocity and orbital achievement.

Contextual Notes

The discussion includes assumptions about constant thrust and neglects factors such as air drag and structural limitations, which may affect the outcomes described.

Labguy
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Don't laugh guys, but I'm familiar with a lot of general astronomy stuff but my question will seem very stupid.,:cry: About rockets, etc.

I was thinking today (dangerous) and realized I don't know the answer to:
Samples: (hypothetical)

1. Space shuttle and all weighs 5 million pounds and total thrust of engines is 6 million pounds, net one million pounds over weight.

2. Payload (any) weighs 500 pounds and thrust in 1,000,500 pounds, net one million pounds over weight.

3. Payload weighs 5 pounds and thrust in 1,000,005 pounds, net one million pounds over weight.

So, not counting air-drag, etc.
Do all three accelerate at the same rate:confused:
Do all three reach same velocity in the same amount of time:confused:
Would all three reach the same orbit (if programmed the same) at the same time and velocity/altitude:confused:

Like I said, dumb question, after midnight, drunk, and I have to pilot an America West flight in 5 hours...:zzz:
 
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No, of course they don't accelerate at the same rate.

F = ma

If you keep the force constant, but decrease mass, you necessarily also increase acceleration.

- Warren

p.s. I hope you're aware of FAA restrictions about alcohol consumption before flying. I wasn't even aware that you were a pilot? :rolleyes:
 
Thrust to weight ratio is a common theme in avionics. Obviously it must be greater than 1 just to get off the ground. For the purpose of getting a payload into orbit, the bigger the better. Getting out of the Earth's gravity well as soon as possible is the objective. One of the more important limiting factors is how much heat the thrusters can tolerate [and how long]. Acceleration stress, which is a form of hoop stress in structural design, is also an issue. It is a complex engineering problem.
 
chroot said:
No, of course they don't accelerate at the same rate.

F = ma

If you keep the force constant, but decrease mass, you necessarily also increase acceleration.

- Warren

p.s. I hope you're aware of FAA restrictions about alcohol consumption before flying. I wasn't even aware that you were a pilot? :rolleyes:
That was easy, I said it was a midnight, drunken-stupor question! Now I'm up early too. I gotta see the doctor for more sleeping pills.

FAA? You mean I'm supposed to follow those rules too? I guess they actually expect me to get a pilot's license too!...:biggrin:
 
Last edited:

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