I Can a plane escape Earth's gravity with a powerful engine and no air?

[ahmed emad]

If I drive a plane and the force of engine is bigger than force of gravity of it , if the engine is turn on always ,and assuming no air , will the plane continue moving up and escape from the gravity ?

 

[jedishrfu]

If there's no air what does the engine push against to propel the plane forward?

Think of a helicopter it can lift folks up higher and higher but then the air thins out and the propeller blades are less effective so that it will level off unable to climb anymore and hence not escape the earth.

 

[ahmed emad]

If there's no air what does the engine push against to propel the plane forward?

Ignore this or make it rocket insted

 

[jedishrfu]

So what do you think and why?

 

[ahmed emad]

I think it will escape from gravity but escape velocity lesson confused me

 

[A Lazy Shisno]

I think it will escape from gravity but escape velocity lesson confused me

You're correct, it will definitely escape. When you pick something up and keep it suspended, you're applying a force equal to gravity upwards, making net acceleration zero. If you have a larger upward force, net acceleration points upwards and so the body will go upwards indefinitely.

Terminal velocity is a bit different. At terminal velocity acceleration still points towards the Earth, but the body is fast enough that it will only come to a stop at infinite distance. This is because as the body moves further away, the force of gravity gets weaker and so velocity decreases at a decreasing rate, proportional to the inverse square law, tending to zero as it approaches infinite distance. Because of this, spacecraft trying to get to a location near to Earth (such as orbit) don't actually require escape velocity as they aren't trying to get away from Earth's gravity completely.

 

[Drakkith]

I think it will escape from gravity but escape velocity lesson confused me

Escape velocity is the velocity something needs to escape an object's gravity if it acquires that velocity at the surface of the object. In other words, if I launch an unpowered projectile from a cannon, it will need to have a velocity equal to or greater than the escape velocity of the Earth in order for it to continue moving forever and not stop and accelerate back towards the Earth at some point. Obviously we're ignoring things like air resistance, gravitational influences of other bodies, the motion of the Earth, etc.

Powered craft, like rockets, can exert a force against gravity while they are in flight and thus they are not required to reach escape velocity. If my spacecraft launches and then reaches a steady velocity of 100 m/s away from the Earth, as long as its engine is exerting enough force to counteract gravity and keep it at 100 m/s then it will continue moving away and will not stop and accelerate back towards the Earth under the force of gravity.

 

[FactChecker]

Escape velocity: momentum is enough to escape with no continuing engine force.
Engine force greater than gravity: may escape at a rate much slower than escape velocity because it is not counting on momentum. The engine is still going.

 

[Janus]

The thing to keep in mind is that escape velocity at any given distance from the Earth's surface decreases with the distance. So if you were to climb away from the Earth at 100 m/s, once you reached a distance of ~80,000,000 km from the Earth, you will be moving at escape velocity for that distance, and you'll be able to cut your engines. In reality, you'd be able to cut your engines long before that, as this figure does not take the gravitational effects other bodies like the Sun have on your craft. Well before you reach this distance from the Earth (somewhere above 2 times the distance of the Moon) , the Sun's tendency to pull you into an independent orbit around it overcome the Earth's pull on you and you would not fall back to Earth if you cut power.