Why does a rocket need no fuel to go around a planet in a fixed orbit?
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First, once you're done accelerating, you don't need to carry fuel. Look at the Pioneer probes. They achieved escape velocity, and now are traveling indefinitely outward.
The thing is, that only works if you want to keep traveling forever. If you actually want to go somewhere, you need to stop when you get there, which means you need enough fuel to decelerate on the other end.
The point, however, is that rockets don't have to continuously fire in space, if they can get out if whatever gravity well they're in. The problem is that getting out of those gravity wells takes a huge amount of fuel.
The thing is, that only works if you want to keep traveling forever. If you actually want to go somewhere, you need to stop when you get there, which means you need enough fuel to decelerate on the other end.
The point, however, is that rockets don't have to continuously fire in space, if they can get out if whatever gravity well they're in. The problem is that getting out of those gravity wells takes a huge amount of fuel.
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Astronomy,
Look first of all, rockets dosn't move around the planets in orbits it's the satellites which revolve around it in fixed orbits.
Now every planet has its own gravitional acveleration i.e.earths gravitional acveleration is 9.8m/sec².
Before going into that l wanna say something.If you through something horizontally to the groung it won't go horizontally.It will bend and will fall down.Here the gravitational acceleration and the velocity are perpendicular to each other but because of air and some other resistance it falls down.
Now if you through a piece of rock from a very tall building i.e. say Burj Khalifa.You will observe that the rock have had gone a good distance and again fall to the ground just like the first observation.Similarly if you keep increasing the velocity at one time it won't fall to the ground and will revolve around the earth as long as any external force is not applied.
And to make it to revolve the velocity,mass and the gravitional acveleration must be in a proportion.
The aeronautics who sent the setalite to orbit any plannet does some complex mathematical solving and finds the exact velocity and angle in which the setalite should be sent.And thus if it orbits the planet it does not require any energy because when the force and the displacement are perpendicular the work done is considered as 0.
Some energy is required i.e. when it was sent,or when you threw the rock
That's it
Hope it helped (≧∇≦)b
Look first of all, rockets dosn't move around the planets in orbits it's the satellites which revolve around it in fixed orbits.
Now every planet has its own gravitional acveleration i.e.earths gravitional acveleration is 9.8m/sec².
Before going into that l wanna say something.If you through something horizontally to the groung it won't go horizontally.It will bend and will fall down.Here the gravitational acceleration and the velocity are perpendicular to each other but because of air and some other resistance it falls down.
Now if you through a piece of rock from a very tall building i.e. say Burj Khalifa.You will observe that the rock have had gone a good distance and again fall to the ground just like the first observation.Similarly if you keep increasing the velocity at one time it won't fall to the ground and will revolve around the earth as long as any external force is not applied.
And to make it to revolve the velocity,mass and the gravitional acveleration must be in a proportion.
The aeronautics who sent the setalite to orbit any plannet does some complex mathematical solving and finds the exact velocity and angle in which the setalite should be sent.And thus if it orbits the planet it does not require any energy because when the force and the displacement are perpendicular the work done is considered as 0.
Some energy is required i.e. when it was sent,or when you threw the rock
That's it
Hope it helped (≧∇≦)b
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