What is escape velocity?

This is the minimum initial velocity required to move from a point to infinity in a gravitational field.

Infinity is defined to have a potential, V of zero; this is the point where the gravitational field has no influence on the object and no force is acting on it due to the gravitational field (in theory). In reality this point of infinity is simply described as a point incredibly far away as though the field is not acting on the object.

Note that the definition does not include the mass of the object and is only concerned with the grav. Field itself.

The formula used to calculate the escape velocity:           V_e = sqrt[2GM/r]

Where G is the Universal gravitational constant; M is the mass of the body producing the grav. Field; r is the radius of the body.

For example, on earth:

The Earth’s mass approximately: M = 6x10^24 kg;

Universal gravitational constant: G = 6.67×10^-11 m^3 kg^-1 s^-2;

Radius of Earth approximately: r = 6,400,000m.

    Sub in the numbers:

    V_e = sqrt[(2)(6x10^24)(6.67×10^-11)/(6,400,000)]

Results in:

The escape velocity of the earth: V_e = 11.2 km/s.

Any object, irrelevant of mass would require this initial velocity to escape the earth.

Space Rockets:

Of course rockets when sent to space, escaping earth’s field they are clearly not travelling anywhere near 11.2 km/s at launch. This is because the rocket is continuously accelerating as it pushes propellant out the exhaust and so travels upwards. Note the careful wording of the definition of escape velocity: “Initial velocity required” so this 11.2 km/s only applies to an object with no further acceleration.

Ashkan P. GCSE Physics tutor, A Level Physics tutor, GCSE Maths tutor...

2 years ago

Answered by Ashkan, an A Level Physics tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist


£20 /hr

Liam M.

Degree: Mathematics (Bachelors) - St. Andrews University

Subjects offered:Physics, Science+ 2 more


“I have a real passion for Maths and Physics and would relish the opportunity to pass this passion on to others! ”

£24 /hr

James T.

Degree: Chemical Engineering (Masters) - Bath University

Subjects offered:Physics, Maths+ 2 more

-Personal Statements-

“Second year Engineer. I love problem-solving and hard work! Everyone works differently and I will find the best way for you to learn and make sessions fun!”

£24 /hr

Joe C.

Degree: General Engineering (Masters) - Durham University

Subjects offered:Physics, Science+ 2 more


“Masters student at Durham University, ready to help you excel at Maths and Science ”

About the author

Ashkan P.

Currently unavailable: for new students

Degree: Medical Physics (Bachelors) - University College London University

Subjects offered:Physics, Maths


“Medical Physics student at UCL here to help you get up to speed with what our species understand about nature.”

MyTutor guarantee

You may also like...

Other A Level Physics questions

Describe how the strong nuclear force between nucleons varies with seperation of the nucleons.

A positively charged particle enters a magnetic field oriented perpendicular to its direction of motion. Does the particle: A) Change its velocity, B) Change its speed, C) Accelerate in the direction of the magnetic field.

How should I structure my experiment report?

A geostationary satellite is orbiting Earth, a) What is meant by a geostationary orbit? b) Calculate the height at which the satellite orbits above the surface of the Earth. The radius of the Earth is 6400km and its mass is 6x10^24 kg.

View A Level Physics tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss