What is gravitational force? Gravitational force is defined as a force of attraction which exerts between two objects with mass. It pulls two objects that have mass. (Gravitation and Gravity) The discovery of gravitational force One day, Newton was sitting on his garden and observing the falling of an apple from a tree. A sudden inspiration appeared in his mind. There must be a force exerted on the apple since the apple accelerated while falling down from the tree with zero initial velocity. The force is then called “gravity” and the acceleration due to the force is called “acceleration due to gravity” (Sir Isaac Newton: The Universal Law of Gravitation). Effects of gravitation on planets If the force of gravity exerts at the top of the trees and mountains, then it must exerts all the way to the orbit of the moon. It is expected that the orbit of the moon around the earth results from the gravitational force as the acceleration due to the gravity can change the velocity of the moon in such a way it followed an orbit around the earth. Kepler’s law of gravitation Kepler’s Third Law states that the ratio of the cubes of their mean distances from the Sun is same as the squares of the periods of any two planets orbit about the Sun. T represents the time taken for one revolution about the Sun and R represents the distance between the planet and the Sun. The equation indicates that the period for the planet to orbit the Sun is proportional to the radius of its orbit. (Johannes Kepler: The Law of Planetary Motion ). However, the accurate measurements on the orbits of the planets showed that they do not precisely follow Kepler’s laws. The validity of the Kepler’s law is corrected by Newton. The mass of the Sun is extremely greater than any other planet. Thus, the force of attraction between planets will be small compared to the force due to the Sun. The law of universal gravitation Law of universal gravitation states that every particle in the universe attracts each another with a force that is proportional to the product of their masses and inversely proportional to the distance apart squared. This force exerts along the line of centers joining the two particles. The magnitude of the gravitational force can be calculated using the formula: F = GMm F is the magnitude of the gravitational force r² G is universal gravitational constant M and m are the masses of the two particles. r is the distance between the two particles. The universal gravitational force is also named universal constant as it is expected to be constant at any times and places. Therefore, it is universally characterized the intrinsic strength of gravitational force (Sir Isaac Newton: The Universal Law of gravitation). The gravitational constant is very small since we are unaware of the existence of the force of attraction between objects. Field strength Gravitational field strength is defined as force, N per unit mass, kg . The definition of gravitational field strength is derived from the Newton’s second law, ΣF=ma . By making acceleration, a , as a subject and then substitute acceleration, a with gravitational field strength, g , and we would obtain a formula, g = F/m . F represents the gravitational force, N whereby m represents the mass of an object, kg . Gravitational field strength close to the earth’s surface is the same as the gravitational acceleration, 9.8Nkg . When the force is not given, gravitational field strength can be calculated by using the formula, g = GM/r² . This formula can be obtained by the substitution of the two equation, F = mg and F = GMm/r² . Hence, resulted in the formation of the equation, g = GM/r² . The greater the value of g , the greater the gravitational field strength (Universal Gravitation and Weight). Future of Gravitation Einstein theorized that gravity can be explained by the curvature of space time. Space time is warped by the mass and energy inside of it but not flat. Objects travel in straight line do not hold by mysterious force but follow the curves in space time. The objects move in straight lines along four-dimensional space time but move in elliptical circles in three-dimensional space. Light appears to travel in straight lines although it is actually bent, curved and changed by the fabric of space time. Although it looks like straight out in front of us, it is actually around the corner of the sun because the space time warp morphs the light. We see only the result of the light that is being bent around the sun. This can not be tested since the sun is shining us right in the eyes and we cannot see the stars. However, it is possible to test out this theory during a total solar eclipse. We are constantly orbiting the sun so we are able to observe the changes of the movement of the star in orbit. Conclusion In conclusion, based on the acceptable Newton’s gravitational law of gravitation, gravitation is a mutual force. Every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Therefore, gravitational force is depends on the masses of the bodies and the distance between the two bodies.

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  1. Doctor Who is now considered a British Institute and has come a long way since it first aired on November 23rd 1963. The very first show saw the Doctor travel 100,00 years into the past to help some dim cavemen discover light. After 26 seasons and seven Doctors later the series came off our screens in 1989 much to the disappointment of the huge devoted fanbase. In 1996 an attempt was made to revive Doctor Who but it wasnt until June 2005 when it came back with a vengeance with Christopher Eccleston as the ninth Doctor that put the series back on the map as it were. It then went on for 5 years with David Tenant portraying the Doctor until 2010 when Matt Smith took over the role. Today it is still a great family show and has attracted many new fans.

    If youre a new or old fan of the show there are Tours and museums you can go and see some of the locations and memorabilia of this classic show. The Doctor Who Tour of London will take you on over 15 locations from the show, some from the new series and some from old sites like the location of The Invasion and Resurrection of the Darleks. The tour also takes you to the TV museum in London where you will get to see some of the cosumes worn in the show and props used. Also you can buy gifts and memorabilia from the shop.

    You will learn all about how the shows were made so the tour is also educational. If you want to take pictures of the locations thats not a problem. Remember the front door of 10 Downing Street in Aliens of London? Well you can get up and close to this and get your picture taken in front of the door. Rose Tyler fans will love the tour as you get to drop by her home in the show.

    Why not go that extra mile and actually meet a Doctor Who star. Well this is possible with private or group tours. You will get the general tour but included will be a pre-arranged meeting or lunch with a celebrity from the show. This will obviously depend on availability of the celebrity and the cost will reflect the popularity of that celebrity.

    There are tours in London and also Wales. The Wales tours take you to Cardiff where you will see lots of location which were featured in shows since 2005. You can leave from London or at Leigh Delamere services station on the M4. There is a Doctor Who exhibition in Cardiff which you get to see. At the end of the Doctor Who tour you get a souvenir group picture sent you by email which is a nice touch.

    For seriously devoted Doctor Who fans there is a 3 day tour which takes you to all the locations in both London and Cardiff. You will see locations from the past 45 years as well as recent sites from the lasted Doctor Who series. Day one is based in London where you get to see 15 sites. Day two takes you to Cardiff where you get to mean the real life owner of the to see we have an Gothic property used as the location of the school in Human Nature. The final day is partly spent in Cardiff with a walking tour at Cardiff Bay, then you head back to London but a stop at Stonehenge to see the site of the Pandoica. Then its dinner at The Cloven Hoof pub in Devils End b efore you taken back to central London.


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