# Orbit Velocity

by on July 6, 2009

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inSatellites in orbit collectg solar power. Image: National Space Society.

What is orbital velocity? In short it’s the velocity required to keep an object in orbit. For you non physics buffs it might help to refresh your memory with what velocity is.

In physics, velocity is the rate of the change in distance, what we call speed, in a certain direction. In physics, characteristics like speed and acceleration are simply numbers. They don’t have meaning and can’t be explained without also having a direction. When these two descriptions, the number and the direction are combined, in physics this is a vector. Velocity then is simply a vector that describes the speed and direction of an object. Orbital velocity is the required speed and direction needed for an object to stay in orbit. This phenomenon happens to all objects in the universe small and monolithic thanks to gravity.

Physics tells us that all things in the Universe exert a pull on each other called gravity. The greater the size and amount of matter something has, the greater the force of gravity it exerts on everything around it. This is why we don’t go flying off the surface of the Earth. Normally if there is a huge enough difference, one object will fall under the influence of the gravity of the bigger object – in this case the Earth. Now in order for space vehicles to enter orbit, they must first escape the Earth’s pull. In order to do this they have to move at a fast enough velocity. This is called the escape velocity. The next happens if you are outside the Earth’s atmosphere but are still in the Earth’s field of gravity. You start to get pulled back to Earth. Now to maintain your position outside Earth – your orbit – you have to move at a fast enough velocity to counteract the pull of the Earth. If you hit the right orbit velocity something interesting happens. Your spacecraft will actually go in the combination of two directions. One is straight ahead and the other is perpendicular to the pull of Earth’s gravity. These two forces will bend the direction your vehicle travels into a circular path – your orbit.

This principal is what keeps every celestial body even entire galaxies spinning in place.

In spaceflight, orbital velocity is what helps us to keep the International Space Station in place above the earth and keeps the shuttle in low earth orbit after it leaves the Earth’s atmosphere. So you can say without an understanding of this principal there could be no space program.

If you enjoyed this article there others one on Universe Today you want to read these related articles. Here is one on the length of a manned flight to mars. This article also mentions orbit velocity in the launch of an experimental space vehicle

Here are some other links you might find informative:Orbital VelocityOrbital Velocity calculator

Source: Wikipedia

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