First of all, I would like to apologise to everyone for being absent all these while. I have been powering down 
1. To fend for some ideas in real life
2. To power up  projects.

Today, I decided to talk about gravity, cause frankly, that was what I learnt today too. 
I am in no classroom, I just read it in a book, and its quite fascinating. 

While yes, we all know about Newtons epiphany with a falling fruit, that doesn't even begin to describe how powerful and enormous this force really is. Through understanding gravity, or rather **gravitational forces** we are able to explain why planets have a certain shape, why certain celestial bodies cant just be wherever they want, and because of gravity, we literally have the perfect planet for life to exist.

# So what is gravity?
http://1.bp.blogspot.com/-pdjean_CUjQ/VbOkuTlL3jI/AAAAAAAAEPU/bv0Xtc_wIcA/s1600/b1.jpg
[source](http://www.waykiwayki.com/2015/07/flat-earth-gravity-is-hoax.html)

Well, for starters, gravity is one of the few forces that can be termed a universal constant. I.e, throughout the universe, gravity acts in the same manner. It is classified as one of the fundamental physical constants.

*A physical constant, sometimes fundamental physical constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time.*
[ref:physical constant wiki](https://en.wikipedia.org/wiki/Physical_constant)

In essence gravity is that which makes matter come together to form asteroids, moons, planets, stars, galaxies, whatever you can think of in terms of the universe, gravity is present. 

If you aren't understanding it, lets simplify it by saying ''gravity is an attracting force between the center of one body, and the center of all other bodies that has mass in the universe''

[ref:Newton law of universal gravitation](https://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation)

Any body that has mass, has a gravitational force that it exerts over a certain area. Whatever other object or mass that comes within range, is captured by that said gravitational pull. 

Your laptop, your phone, your house, yourself etc all have a gravitational pull exerting on each other, however, it is highly negligible. The more mass an object has, the more gravitational pull it is able to exert on objects around it.

In outer space, things become more easier to see, but more trickier to understand.
There are laws which govern the priciples of gravity.

According to [Newton law of universal gravitation](https://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation),  the attractive force (F) between two point-like bodies is directly proportional to the product of their masses (m1 and m2), and inversely proportional to the square of the distance, r, (inverse-square law) between them:

![Screenshot (622).png](https://steemitimages.com/DQmUDuzJKWidNTin7xvwRhqfRvadcy8pE7nU6C9cgUdCv5C/Screenshot%20(622).png)
[ref: earth-moon movement](https://cseligman.com/text/moons/earthmoongravity.htm)

[ref:gravitational constant](https://en.wikipedia.org/wiki/Gravitational_constant)

# gravity slingshot
https://s-i.huffpost.com/gen/1380904/images/o-SPACE-TIME-facebook.jpg
[source](https://www.huffingtonpost.com/2013/09/30/space-time-curvature-microchip_n_4016322.html)

In many space bound movies, there always comes a time when the crew of the ship is in dire need to gain speed, or loss some foe, and the captain then decides to run for the nearest star and make a slingshot around it, using the gravity to gain momentum and speed out-system or wherever they wish to go. 

Believe it or not, it is actually a really real phenomenon and it is termed gravity assist.
The concept is one that is fairly simple. 

Supose you are a space faring fellow, with cans of illegal cat food and the interstellar police gives pursuit. You could lose the police in a cloud of debris, or you could take a swing by a planet and use the gravitational force to push you out at high speed.

This works because gravity is a force that attracts, meaning as you get closer to the planet, you're pulled more strongly towards its center, essentially falling through the planet, which would happen unless you make calculations and set your propulsion carefully.

*In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft*
[ref:gravity assist](https://en.wikipedia.org/wiki/Gravity_assist)

Gravity assist is a concept that had already been used in the past and multiple times at that. Perhaps  one of the most important use of this method of propulsion and course alteration, is in the use for interplanetary probes.

The uses of gravity assist are limitless. 
A spacecraft could swing by the sun and use its gravitational pull to swing outsystem at neck breaking speeds.

Seeing as this could change the speed and and path, several applications for uses could be undergone. 

It could be an inexpensive way to propel more probes for example.

This and many more examples are some of the uses of gravity assist.
***
For more reading:
[1](http://www.independent.co.uk/news/science/the-core-of-truth-behind-sir-isaac-newtons-apple-1870915.html)
[gravitationalpull brtween moon and earth](https://www.quora.com/What-is-the-gravitational-force-between-the-earth-and-the-moon)
[sun slingshot](https://www.quora.com/Can-we-use-the-gravity-of-the-sun-to-slingshot-spacecraft-into-interstellar-space-or-to-other-stars)