Vojtěch asked in Science & MathematicsPhysics · 3 weeks ago

# Can someone explain to me "escape velocity"?

Esp. why does a rocket needs to reach approx. 11,186 m/s to escape gravity field of the Earth? If I would travel CONSTANTLY just 1 m/s (using a lift for example, or really slow rocket), wouldn't I get there too?

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• Amy
Lv 7
3 weeks ago

As others have said already, escape velocity is the speed you need to coast out of Earth's gravity when you have no upward force.

A "really slow rocket" would also get you there. But the rocket would have to lift itself in addition to lifting you.

• 3 weeks ago

Once you get up to escape velocity you can switch the engine off and coast away. Like driving up a hill, once you get enough speed you will go over the summit regardless.

• Steven
Lv 7
3 weeks ago

If you had an unlimited rocket that could keep supporting your weight then you wouldn't need velocity but no rocket is unlimited. So to stay in space you have to orbit real fast so that the centrifugal force due to your velocity cancels your weight so that you are "weightless". While in orbit your kinetic energy is equal to the potential energy due to your altitude but that is a poor explanation. There is no distance where gravity stops pulling you towards the nearest planet, moon etc. so you have to keep moving.

• 3 weeks ago

I'm going to assume that you understand the concepts of potential and kinetic energies. Escape velocity is obtained by setting setting the potential energy of the earth's gravitational field equal to the kinetic energy of an object and solving for velocity.

It is, therefore, the velocity an object needs to have in order to escape from the earth's gravitational pull. Slower than that an object will fall back to earth.

Also, an object in space, with no initial velocity, caught in the earth's gravitational field will strike the ground at escape velocity.

In your specific example a rocket with enough fuel could keep going at 1 m/s and escape the earth into space. This isn't really related to escape velocity since you are continuously adding to the rockets kinetic energy with the potential chemical energy of the rocket fuel.

• D g
Lv 7
3 weeks ago

0.5mv^2 is the energy  kinetic energy of something moving

The potential from gravity is mg∆h

You want to move far enough so the gravitational field from the earth  is less then the acceleration of the object moving away

So gravity on the surface of the earth  is 9.8 m/s^2

Double the distance the acceleration drops by 1/4

Escape velocity  is the velocity needed to reach the point where you are free from being pulled back to the earth

• 3 weeks ago

Yes, you don't need to go at the escape velocity to leave the planet completely. Escape velocity is the initial speed an object must have to leave the planet's gravity completely IF no other forces act on it except gravity. But the rocket engine is constantly giving the rocket thrust, so escape velocity doesn't apply.

If you throw a rock up in the air, you must give it Earth's escape velocity, 25000 miles per hr, in order for it to never come back down.

• 3 weeks ago

It takes a certain amount of ENERGY to escape the earth.  That could be added via a steady slow lift.  Just as you claim.  A steady speed with a constant force CAN get you out of gravity.  It isn't the only way though. If we give something kinetic energy and then stop pushing it the object may still have enough energy to escape.  The escape velocity is the velocity which gives enough kinetic energy that the object will "coast" out of the gravity of the earth like coasting up a hill on a bike if you have enough speed.

• Zirp
Lv 7
3 weeks ago

a really slow rocket wouldn't just take ages to get there, it would also require immense amounts of fuel

• 3 weeks ago

A spacecraft leaving the surface of Earth, for example, needs to be going about 11 kilometers (7 miles) per second, or over 40,000 kilometers per hour (25,000 miles per hour), to enter orbit. Achieving escape velocity is one of the biggest challenges facing space travel.

• 3 weeks ago

the escape velocity you found is for free moving object, not a powered one

in this case gravity will slow the object

and at a velocity less than escape velocity the object would come to a stop and fall back to the ground

if g on the object were constant then it would stop and fall no matter the speed

but g decreases by the square of the distance from the center of the Earth so a sufficient speed will carry an object clear of Earth's gravity

When you get a good response,