Question about rocket engines

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Question about rocket engines

Postby wyattgagar on May 11th, 2017, 3:10 pm 

If a rocket is held stationary does it exert force on non stationary, solid objects?
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Re: Question about rocket engines

Postby BurtJordaan on May 11th, 2017, 3:48 pm 

wyattgagar » 11 May 2017, 21:10 wrote:If a rocket is held stationary does it exert force on non stationary, solid objects?


Please first define precisely what you mean by "stationary" and "non-stationary". These are relative concepts and have no meaning outside of a specified scenario.
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Re: Question about rocket engines

Postby wyattgagar on May 11th, 2017, 3:58 pm 

If you bolted a rocket to the ground and aimed it at a fan would it spin the fan?
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Re: Question about rocket engines

Postby BurtJordaan on May 11th, 2017, 4:26 pm 

wyattgagar » 11 May 2017, 21:58 wrote:If you bolted a rocket to the ground and aimed it at a fan would it spin the fan?

Only if some of the exhaust gasses are deflected upward and can reach the fan. Why do you ask?
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Re: Question about rocket engines

Postby wyattgagar on May 11th, 2017, 4:32 pm 

If a rocket was bolted down and aimed at a piece of carbon on a track, would it push the piece of carbon down the track. I just want to know if instead of propelling the rocket would a stationary rocket repel a different object that is free to move.
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Re: Question about rocket engines

Postby BurtJordaan on May 11th, 2017, 5:50 pm 

No, it won't if bolted down. Only things behind it will be 'blown away'. There are no forces "going to the front" - they are all just against the bolts holding it down.
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Re: Question about rocket engines

Postby wyattgagar on May 11th, 2017, 5:53 pm 

Okay my question was will the object get blown away. Which I believe you just answered. Thank you.
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Re: Question about rocket engines

Postby Dave_Oblad on May 11th, 2017, 6:46 pm 

Hi wyattgagar,

Yes, if you count the exhaust as a force. YouTube had a video that showed a car get blown off a road as it passed behind a Jet that was preparing to take off but still had its brakes on.

Whatever is holding the Rocket stationary will feel the force of the rocket as pressure, but that pressure is not transferred through the ground to other objects.

Note: The exhaust is not pushing the rocket forward (exactly). If you vented the exhaust to all sides at right angles, the rocket will still try to move forward (I'm pretty sure). The pressure to move forward is located inside the rocket engine.

That help?

Regards,
Dave :^)
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Re: Question about rocket engines

Postby Braininvat on May 11th, 2017, 7:28 pm 

Actually, a very infinitesimal force is transmitted through whatever the rocket is bolted to and to the earth that the testing stand rests on. If the engine was discharging westward, then the thrust would cause a tiny deformation eastward in the earth's crust, wouldn't it? ( if the crust were perfectly rigid, the thrust would accelerate the rotation of the earth by a tiny amount, too small to measure....)
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