*Question by Lovely*: I need the people who knows well about science (physics)?

I would really appreciate it if you could help me with this question. Two new terms from this session are escape velocity and orbital velocity. Orbital velocity is the velocity that is required to keep an object moving in a particular orbit. Orbital velocity changes depending on the distance from the Earth at which you want to have an object orbit.

Why is this true?

**Best answer:**

*Answer by Matt C*

Because orbital velocity is related to centripetal force. To find orbital velocity you have to equate the force of gravity on the object and the centripetal force on the object. Both of these forces are dependant upon the radius (distance from the center of the body they are orbiting around) so the speed with which the object must move is also dependent upon the radius.

The equations:

Fg = Gm1m2/ r^2

Fc = m1 v^2 / r

setting them equal and cancelling

v^2 = Gm2 / r

v = sqrt (G*m2/ r)

so v will be proportional to 1 / sqrt(r)

**Give your answer to this question below!**

Keeping an object in a particular orbit requires keeping it at a specific altitude, which is the distance from the object that it is orbiting about.

In order for this to happen, the sum of forces acting on the satellite along the axis between the two objects must be zero, as the satellite must not be accelerating toward or away from the planet.

So what are the forces acting on the satellite? One is gravitational force, the other is centripetal force; both depend on the mass of the satellite and the respective accelerations. The formula for both gravitational and centripetal acceleration depend on the distance between the two objects, but the centripetal acceleration also depends on the orbital velocity of the satellite.

Look up the formulas to compare them. It should make sense that the greater the distance from the Earth, the lower the orbital velocity.