Why is escape velocity necessary

How do we put a spacecraft into orbit? Once a ship is in orbit, do we have to do anything to keep it there? How did DS1 get into space? Could NASA use ion propulsion to put a ship into space? Create a free Team What is Teams? Learn more. I don't understand why escape velocity is necessary [duplicate] Ask Question. Asked 2 years, 9 months ago. Active 1 year, 7 months ago. Viewed 5k times.

Improve this question. Ambrose Swasey. Ambrose Swasey Ambrose Swasey 3, 6 6 gold badges 25 25 silver badges 54 54 bronze badges. Mind you, gravity does not just stop at one point, it only decreases with the squared distance. If you want to properly escape gravity, ie. Eventually, as you get far enough from the Earth, it will drop below 50 mph. Well, it would, if the Earth was floating alone in interstellar space.

In practice, the Sun's gravity will start to dominate long before that happens. Who says you can't do this? If you look at the derivation of escape velocity, it is pretty obvious that you are assuming that you start off with the escape velocity and don't apply any other forces afterwards.

Also, if it's your intent to send a probe that goes 50 miles per hour all the way to the Sun, it's not even going to get half way there during your lifetime. Space is Big! Show 3 more comments. Active Oldest Votes. Improve this answer. Birds and the bees. Phil Cohen, Sydney Australia In a way, you are right. However, where the 11km per hour comes in is that it is the speed at which an object, rather than being held in orbit around the earth or falling back to it due to gravity, will be thrown outwards by sufficient centrifugal force to describe an open curve away from the planet.

John Ramsey, Hackney UK Providing that you can keep your propulsion system going and the thrust is greater then gravitational pull back to Earth, yes any speed will do. Once you reach escape velocity however you are going fast enough to escape the Earth's gravitational pull without doing any more work, you can turn your engines off and you'll still keep going never to return. The escape velocity is the speed you need to avoid this fate and keep travelling forever, although you would need to travel at a much higher speed if you wanted to reach the stars in your lifetime.

M Baillie, Sawston UK If you throw something up in the air, it will carry on rising until the force of gravity overcomes the velocity of the object and causes it to keep slowing until it stops and then starts falling back to earth. You are kind of correct in saying that you just need to "keep going up", but in order to keep going up you need a sufficient amount of velocity to overcome the force of gravity.

The amount of velocity needed to escape our planets gravity is approx 11km per second, which is known as escape velocity. The assumption is that no further force is applied to the object once it has set off.

Of course any velocity will do if continued force is applied to the object, just as a car being driven uphill will keep going if enough power from the engine is applied via the accelerator. As you say, any speed will do. Escape velocity is simply the speed that theoretically would be sufficient to remove something from Earth's gravitational influence with no further impulse required.

Michael Fisher, Brisbane Australia Escape velocity is the speed required to escape gravity in the absence of any force being applied. To keep going up requires the continual application of force. So yes, of course it is possible to keep going upwards and further from the earth, but without reaching escape velocity you would eventually be pulled back to earth when the fuel runs out.

Clive Gordon, Ruislip UK Escape velocity is literally the velocity which an object would need to be projected in order to leave the surface of a planet or other body in space. If the object were subjected to a steady upward force just greater than its weight,instead of an explosion,it would eventually leave, but much more slowly.

It is interesting to note that the speed of air molecules is too low to allow them to escape the Earth, but greater than the Moon's escape velocity.

That's why we have an atmosphere and the Moon hasn't. Is this rocket science? If you have enough power you can trundle up at your leisure. This point was ably covered in the old Peter Sellers movie "mouse on the Moon" which had a steam kettle spaceship. Rockets usually just have to get high enough to fall into orbit.

However, you do need to get a rocket up to a high velocity before its fuel runs out if you want to send a probe to another planet. Phil Barker, Edinburgh Scotland The escape velocity refers to an the speed an object needs to achieve to move from its current point in a gravitational field to infinity as the gravitational field has no distinct end point , it is equal to the speed that the object would be traveling at if it was pulled by the same gravitational field from infinity to that same point.

However this only applies for an unpowered mass that would be constantly decelerating due to the gravitational pull of the plant and you are quite right in saying a powered mass would be able to escape no matter what its speed. Fully 0. But, as we shall see, it is these 0. As an illustration of a Boltzman-like distribution, think of cars on the interstate. Most are moving at speeds close to the speed limit of 65 mph.

However, a few are moving faster and a few are moving slower. And perhaps 1 out of ever cars is moving mph while another 1 out of is puttering along at 45 mph. Now supposed that a highway patrol officer pulls over and tickets the mph driver. What happens? Someone else speeds up and replaces the fastest car so that there is always one bozo driving much too fast.

At the distance of the snow line let's call this 5 AU , the temperature of material illuminated and heated by the Sun is about K C. Thus, the averge velocity of a hydrogen atom. Clearly, even our average H 2 molecule 1. So quickly, all the hydrogen would escape from the Moon to space. This means that the fastest few molecules will escape. Once they escape, a few other molecules will find there way to higher speeds and then they will escape.