Why does a satellite revolves earth in a circular path
Answers
Gravity attracts all things towards each other
Every object in the Universe is being attracted towards every other object by the force of gravity. This means that there is nowhere you can go in the Universe where gravity is not acting. Examples of gravity in action:
Gravity holds the atmosphere in place around the Earth.
Gravity keeps people on the Earth’s surface.
Gravity keeps the International Space Station in orbit around the Earth.
Gravity keeps the Moon orbiting around the Earth.
Gravity keeps the Earth orbiting around the Sun.
Isaac Newton was the first to come up with the idea that all objects are attracted towards each other by gravity. Even people are attracted towards each other by gravity, but this force is so small that it is not noticeable. Gravity only becomes noticeable if one (or both) of the objects has a lot of mass, such as the Earth.
There is gravity in space
Earth-Moon system and gravity
Any two masses are attracted towards each other by gravity. This force of gravity causes the Moon to change direction to make it orbit around the Earth.
Gravity doesn’t disappear just because you are above the atmosphere. Even if an object is high above the Earth’s atmosphere, there will still be a strong force of gravity pulling it towards the centre of the Earth. At an altitude of 30 km, you would be above 99% of the Earth’s atmosphere. At 100 km, you would officially be in space, yet the weight force of gravity would still be nearly the same. You and the Earth would still be pulled together.
Newton worked out that, if the distance from the centre of the Earth doubles, gravity becomes a quarter as much as it was on the surface. A satellite with a mass of 1000 kg has a weight force of 9800 N at the Earth’s surface. The radius of the Earth is about 6366 km, so at 6366 km above the Earth’s surface, the distance from the centre of the Earth will have doubled. The weight force pulling it towards the centre of the Earth will now only be a quarter as much but will still be 2450 N.
So why doesn’t a 1000 kg satellite just fall back to Earth?
Sideways speed keeps satellites in orbit
Satellite speed and force directions
As a satellite moves around the Earth in a circular orbit, the direction of the force of gravity is always towards the centre of the Earth.
At an altitude of 100 km, you would be so high that you would see black sky and stars if you looked upwards. If you took a satellite to this height and released it, it would still fall towards the Earth because the force of gravity is nearly the same as it is at the Earth’s surface.
However, if the satellite is given speed in any direction horizontal to the surface of the Earth, it will travel further before it hits the Earth. If it is given enough speed, it will travel so far that, as it curves towards the Earth, it will miss the Earth altogether. At just the right speed, it will move around the Earth in a circular motion. This type of motion and the path that a satellite moves in is called an orbit.
Close to the Earth at an altitude of 100 km, a satellite needs to be moving at 8 kilometres per second (28 000 km/h) to stay in orbit. At higher altitudes, satellites do not need to be travelling as fast. Television communication satellites are at a higher altitude of 36 000 km and only need to travel at 3 km/s (11,000 km/h).
The Moon is 360,000 km from the Earth and only needs to be travelling at 1 km/s to stay in orbit around the Earth.