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Gravity & satellite motion



What is Gravity?

YouTube Video



Gravity
 is a force that attracts all objects towards each other. People are attracted towards the Earth and the Earth towards people,

 the Moon and the Earth are attracted towards each other, and the Sun and the Earth are attracted towards each other.

All of these attractions are caused by 
gravity.

- Gravitational attraction is greater for more massive objects

 
- Gravity
 decreases as distance between the objects increases. 


 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.

gravity and the motion od the satellites


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.


So the closer the satellite from the surface of the Earth the faster it travels and vise versa.


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