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[Gaz]

On the Jet - Own Air Supply Comment - the same would apply to a propeller.

Ion Rockets fine i don't want to go into that much detial even so they are still expelling somthing to create thrust.

a Catherine wheel isn't torque its just vectored thrust.

torque is the rotational force down a shaft i.e turning a scew for example.

I do agree that an internal combustion engine creates torque but the engine is only one part of the system which includes the car and whatever it is sitting on, sit a car on a trolly and accelerate. The car accelerates in one direction and the trolly accelerates in the other, the means by which that force is applied is irrelavent, it could be electromagnetic, it could be tractive (rolling wheels or walking on legs), it could be explosive etc. The trolly the car is sitting on is the propellent, in the case of a car on the ground it would be planet Earth that is the propellent..

The earth isn't generating any energy apart from pulling the car down with gravity and other natural occourances such as wind ect.. The force being applyed to the car is the torque twisting the cars axle in order to turn the wheels.

[f1ea]

Longbow is right. The way cars turn power into motion (acceleration) is by friction at the tires. The way jets turn power into motion (acceleration) is by creating a pressure gradient (difference), which generates a force called thrust.

I disagree, the ground the car is sitting on is the propellent.

No it isnt. In rocket and jet engines, the fuel/air mass being propelled is part of the initial system, while the road (mass) is never part of the system. The fuel the car/jet carry is.

[stonemonkey]

the road (mass) is never part of the system.

because the earth is so massive you have probably been told that and believe it. You only have to read my example of the car on the trolly to see it's not true though.

The earth isn't generating any energy

In the case of a rocket, the rocket is pushing against the propellent. What energy is the rocket generating?

a Catherine wheel isn't torque its just vectored thrust.

torque is the rotational force down a shaft i.e turning a scew for example.

Go on then, fit a shaft to the catherinewheel.


And no one has yet told me if they think my internal combustion engine powered tennis ball launcher in space will produce thrust or not.

[Gaz]

In the case of a rocket, the rocket is pushing against the propellent. What energy is the rocket generating?

What? the Rocket exhaust is pushing against the earth and air while in earths gravity and when it exits earths gravity its just pushing away exhaust away from it self moving it in the oposite direction.

Go on then, fit a shaft to the catherinewheel.

It wouldn't spin.

honestly a car engine does not generate thrust nor does a car.

[stonemonkey]

What? the Rocket exhaust is pushing against the earth and air while in earths gravity and when it exits earths gravity its just pushing away exhaust away from it self moving it in the oposite direction.

Ah now I see, you don't know what you're talking about.

stonemonkey wrote:
Go on then, fit a shaft to the catherinewheel.



It wouldn't spin.

You really don't know what you're talking about.

[Gaz]

Check out the relationship between hp and torque at the bottom of this article:
http://tinyurl.com/b5twu7

Then gather the data for an F1 car (hp, rpm), do the math and plug the result into this table:

http://www.edriveactuators.com/mttorque.html

Does this help?
Let me know the result...

The 2nd is the torque of a engine (prob diesel) vs the thrust produced when the engine is used to pump air for an pnumatic actuator.

Which i guess you could use to show how well a f1 engine would do it

but its not really the same kind of thrust as a jet or propeller plane

[Gaz]

What? the Rocket exhaust is pushing against the earth and air while in earths gravity and when it exits earths gravity its just pushing away exhaust away from it self moving it in the oposite direction.

Ah now I see, you don't know what you're talking about.

Why is that not how a rocket works? ejects mass at a surficant dencity to create an equal and oppsite rection.

For example the shuttle at launch weights about 4 million pounds but the shuttles solid fuel rockets can generate 3.3 million pounds EACH (theres two) thefore it creates an equal and oppsite reaction.


Thrust will always move you in the opposite direction you orginaly sent the mass

So if you throw a brick away from it you'll move in the opposite direction.

However torque is an angular force it acts upon the axel rotating it or on the tyre pushing against the road forcing it to rotate.

Think i know what i'm talking about, and your the one is abit confused.

[stonemonkey]

I'm going to have one last go at explaining this.

You are floating free in space and you have a brick floating next to you, you grab the brick and accelerate it (by any means, spring, throw, spinning wheel) away from you. The brick accelerates and ends up travelling in one direction and you accelerate and end up travelling in the opposite direction slower than the brick because you have a larger mass. That is thrust, forces acting on two masses accelerating them in opposite directions.

Ignoring gravity and atmospherefor a moment, consider a car. The cars wheels turn and the rubber in contact with the ground exerts a force against the ground in one direction. The car will accelerate in one direction and the ground will accelerate in the opposite direction (the earth is massive but is not immovable). once the wheels lose contact with the ground it will continue to travel in one direction and the planet much much more slowly in the opposite (probably both the car and planet having some induced torque due to the line of the force being applied not passing through the centers of gravity). Again that is thrust, forces acting on two masses accelerating them in opposite directions.

Now, if we bring in gravity that will stop the car from escaping and keep it on the ground so that it can continue applying thrust. Thrust can even be applied in the opposite direction in the form of braking, still accelerating the two masses in opposite directions but those directions now reversed.

[stonemonkey]

What? the Rocket exhaust is pushing against the earth and air while in earths gravity and when it exits earths gravity its just pushing away exhaust away from it self moving it in the oposite direction.

Ah now I see, you don't know what you're talking about.

Why is that not how a rocket works? ejects mass at a surficant dencity to create an equal and oppsite rection.

For example the shuttle at launch weights about 4 million pounds but the shuttles solid fuel rockets can generate 3.3 million pounds EACH (theres two) thefore it creates an equal and oppsite reaction.


Thrust will always move you in the opposite direction you orginaly sent the mass

So if you throw a brick away from it you'll move in the opposite direction.

However torque is an angular force it acts upon the axel rotating it or on the tyre pushing against the road forcing it to rotate.

Think i know what i'm talking about, and your the one is abit confused.

You're right in what you're saying about thrust there, previously you said the exhaust was pushing against the ground/air which is not the case and is also not the case with a jet.

A jet or rocket expells the relatively light gas at high velocity,

(mass of gas*acceleration of gas)=(mass of rocket*acceleration of rocket)

so to get a heavy rocket to move the acceleration of the gas must be very high

On the other hand, with the car and the planet

(mass of car*acceleration of car)=(mass of planet*acceleration of planet)

since the planet is very massive it's acceleration due to the force is extremely small compared to the acceleration of the car.

[f1ea]

once the wheels lose contact with the ground it will continue to travel in one direction and the planet much much more slowly in the opposite (probably both the car and planet having some induced torque due to the line of the force being applied not passing through the centers of gravity). Again that is thrust, forces acting on two masses accelerating them in opposite directions.

You seem to be confusing VELOCITY with ACCELERATION. Forces generate acceleration, which is change of velocity.
As soon as the car's wheel lose contact with the surface, providing air friction and all such forces are neglected , the car will cease to accelerate and will therefore keep a constant velocity (if as you mention all other forces are ignored like air friction, gravity etc). No matter how fast the wheels rotate the car will no longer accelerate, regardless of how much power or torque the engine is producing (in reality, it will generate a VERY small acceleration because of the air exiting the ehaust and the tires rotating, but nothing compared to the thrust generated by a jet engine).

But... i just noticed you're from another planet. So maybe that explains it

[texasmr2]

Why does this thread remind me so much of the monkey thread!

[stonemonkey]

once the wheels lose contact with the ground it will continue to travel in one direction and the planet much much more slowly in the opposite (probably both the car and planet having some induced torque due to the line of the force being applied not passing through the centers of gravity). Again that is thrust, forces acting on two masses accelerating them in opposite directions.

You seem to be confusing VELOCITY with ACCELERATION. Forces generate acceleration, which is change of velocity.
As soon as the car's wheel lose contact with the surface, providing air friction and all such forces are neglected , the car will cease to accelerate and will therefore keep a constant velocity (if as you mention all other forces are ignored like air friction, gravity etc). No matter how fast the wheels rotate the car will no longer accelerate, regardless of how much power or torque the engine is producing (in reality, it will generate a VERY small acceleration because of the air exiting the ehaust and the tires rotating, but nothing compared to the thrust generated by a jet engine).

But... i just noticed you're from another planet. So maybe that explains it

I think I said continue to travel as oppsoed to continue to accelerate once the wheels lose contact with the ground.

EDIT:

or are you meaning that because a car that isn't in contact with the ground can't accelerate then it cannot be generating thrust?

If that's the case then please read previous posts where I've stated that the ground/earth is the cars propellant, if a rocket loses contact with it's propellant (expells all it's propellant) it can no longer accelerate either.

[Gaz]

What? the Rocket exhaust is pushing against the earth and air while in earths gravity and when it exits earths gravity its just pushing away exhaust away from it self moving it in the oposite direction.

Ah now I see, you don't know what you're talking about.

Why is that not how a rocket works? ejects mass at a surficant dencity to create an equal and oppsite rection.

For example the shuttle at launch weights about 4 million pounds but the shuttles solid fuel rockets can generate 3.3 million pounds EACH (theres two) thefore it creates an equal and oppsite reaction.


Thrust will always move you in the opposite direction you orginaly sent the mass

So if you throw a brick away from it you'll move in the opposite direction.

However torque is an angular force it acts upon the axel rotating it or on the tyre pushing against the road forcing it to rotate.

Think i know what i'm talking about, and your the one is abit confused.

You're right in what you're saying about thrust there, previously you said the exhaust was pushing against the ground/air which is not the case and is also not the case with a jet.

A jet or rocket expells the relatively light gas at high velocity,

(mass of gas*acceleration of gas)=(mass of rocket*acceleration of rocket)

so to get a heavy rocket to move the acceleration of the gas must be very high

On the other hand, with the car and the planet

(mass of car*acceleration of car)=(mass of planet*acceleration of planet)

since the planet is very massive it's acceleration due to the force is extremely small compared to the acceleration of the car.

Yeh that came out wrong, kinda ment it was being slowed down by it?

pushing against it that way.

Eitherway a car don't produce thrust right?

[stonemonkey]

Yeh that came out wrong, kinda ment it was being slowed down by it?

pushing against it that way.

Ah right, I see what you mean now, sorry.

Eitherway a car don't produce thrust right?

Do you agree or not with this:

When a car is sitting on an trolly and accelerates, the car will accelerate in one direction and the trolly it is sitting on will accelerate in the opposite direction

and, ignoring rolling and drag resistance

(mass of car*acceleration of car)=(mass of trolly*acceleration of trolly)

[welshie]