How do you calculate the Earth's escape velocity?

The escape velocity is the speed that an object must have in order to have enough energy to escape the Earth's gravitational field. To calculate the escape velocity, we can apply the principle of Conservation of Energy, which states that energy cannot be created or destroyed. We equate the total energy that the body has when it is on the surface of the Earth with the total energy it has when it is infintely far away and no longer experiences the Earth's gravity:


Energy on the surface of Earth = Energy at infinity


The total energy at each point will be the sum of the kinetic energy of the body (0.5*m*v2) and its gravitational potential energy (-G*M*m/R).


On the surface of the Earth, it's kinetic energy will be 0.5*m*ve2, where ve is its escape velocity. It's gravitational potential energy will be -G*M*m/R0, where R0 is the radius of the Earth. We assume that the object has just enough energy to reach infinitely far away from the Earth, which means that it has no kinetic energy once it has reached infinity, and has therefore come to rest. It's gravitational energy will also be zero at infinity, because that is how gravitational potential energy is defined (you can see from the expression for gravitational potential energy that as the distance R becomes very large, i.e. infinitely large, it becomes infinitely small).


We place all of these quantities in the expression above to obtain:


0.5*m*ve2 – G*M*m/R0 = 0 + 0


We can cancel the mass of the body, m, from everything on the left hand side:


0.5*ve2 – G*M/R0 = 0


And move the G*M/R0 onto the right hand side:


0.5*ve2 = G*M/R0


We multiply everything by 2 and take the square root to make ve the subject of the formula:


ve = (2*G*M/R0)0.5


Substituting in some numbers (G = 6.67x10-11 m3 kg-1 s-2, M = 5.97x1024 kg, R0 = 6.271x106 m):


ve = 11.2 km/s


It is important to note here that we are neglecting the effects of air resistance as is often done in these calculations. Air resistance would transfer energy from the escaping object into thermal energy in the atmosphere, reducing the object's total energy as time passed. Therefore, more energy would be required at the start, and hence the speed at the start would need to be higher.

Aldo E. GCSE Maths tutor, A Level Maths tutor, A Level Further Mathem...

2 years ago

Answered by Aldo, an A Level Physics tutor with MyTutor

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


£22 /hr

Amilah C.

Degree: Physics with a year abroad (Masters) - Edinburgh University

Subjects offered:Physics, Maths+ 1 more


“Hi there, welcome to me page! About Me: I am currently studying Physics at the University of Edinburgh. From a young age, science has always been a passion of mine, and hopefully I can convey this in my tutorials. Previously, I found...”

£22 /hr

Dan B.

Degree: MPhys Physics (Masters) - Exeter University

Subjects offered:Physics, Maths


“Hi I'm Dan and I'm in the first year of a four-year MPhys Physics degree at the University of Exeter. I am very patient and will tailor the sessions' content and pace to suit your individual needs...”

£20 /hr

Alex R.

Degree: Physics (Masters) - Edinburgh University

Subjects offered:Physics, Music+ 3 more


“About Me: I am a Physics student at the University of Edinburgh, however I also study Computer Science. I believe there is a beauty to Science and Mathematics, however it requires hard work and understanding to be fully appreciated. I ...”

About the author

Aldo E.

Currently unavailable: for regular students

Degree: Engineering (Masters) - Cambridge University

Subjects offered:Physics, Maths+ 1 more

Further Mathematics

“Hi, I'm Aldo! I'm a Cambridge engineer and I'm passionate about maths and physics, as well as passing on knowledge to others!”

You may also like...

Posts by Aldo

How do you calculate the Earth's escape velocity?

How do you find the cube root of z = 1 + i?

Other A Level Physics questions

The speed of water moving through a turbine is 2.5 m/s. Show that the mass of water passing through an area of 500 metres squared in one second is about 1 x 10^6 kg (density of sea water = 1030 kg/m^3)

With the help of a suitably labelled graph, explain what is meant by resonance of a mechanical system.

What is the Centripetal force, and how does it keep objects in circular motion?

What is the Schwarzschild radius of a black hole?

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