What is escape velocity?
In physics, escape velocity is the minimum speed needed for an object to "break free" from the gravitational attraction of a massive body (that is, to escape a massive body without ever falling back).
In other words, an object has to overcome the gravitational pull of a massive body for being free to escape into space.
For example, a rocket going into space needs to reach the escape velocity in order to make it off Earth and get into space.
A larger planet has more mass and requires a much greater escape velocity than a smaller planet with less mass.
More particularly, escape velocity is the speed at which the sum of an object's kinetic energy and its gravitational potential energy is equal to zero.
So, if the kinetic energy of an object, launched from the Earth, were equal in magnitude to the potential energy, then in the absence of friction resistance it could escape from the Earth.
A rocket moving out of a gravity well does not actually need to attain escape velocity to escape, but could achieve the same result (escape) at any speed with a suitable mode of propulsion and sufficient propellant to provide the accelerating force on the object to escape. Escape velocity is only required to send a ballistic object on a trajectory that will allow the object to escape the gravity well of the mass M.
In closing, for example the escape velocity from Earth is about 11.2 km/s or 40,270 km/h (25,020 mph).
This topic isn't so simple, therefore an animation like this below can help its understanding, in particular by the kids.
► Here's how fast you'd have to go to leave every planet in the solar system in one tidy, animated GIF from Tech Insider>>
Fourther reading for deepening
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