• Question: What is the definition of gravity

    Asked by Jack to David, Gemma, Juhi, Matt, Stéphane, Yinka on 8 Mar 2018.
    • Photo: Stéphane Berneau

      Stéphane Berneau answered on 8 Mar 2018:

      Hi Jack,

      Gravity is the force of attraction of a mass compared to others. Therefore, the planet Earth generates gravity and make us humans stay on it. We are experiencing it all the time. As soon as you jump on the air, the gravity pulls out down to the ground.
      The force was first identified by Sir Isaac Newton. Have you heard the story about Newton staying under an apple tree?

    • Photo: Gemma Chandratillake

      Gemma Chandratillake answered on 10 Mar 2018:

      We don’t really know what gravity “is”, we only really know how it behaves. It is defined as the force of attraction that exists between any two objects that have mass (e.g. any two particles, or an object and the Earth). It is the force of attraction that exists between all objects, everywhere in the universe. Objects with more mass have more gravity. Gravity also gets weaker as the distance between the objects increases. So, the closer objects are to each other, the stronger their gravitational pull is.

      The gravitational equation says that the force of gravity is proportional to the product of the two masses (m1 and m2), and inversely proportional to the square of the distance (r) between their centres of mass. Mathematically speaking:

      F=Gm1m2 / r*r,

      where G is called the Gravitational Constant. It has a value of 6.6726 x 10-11 m3 kg-1 s-2 (sorry –
      I can’t work out how to do powers on here, so if you’re interested, look it up to get the correct way of writing the Constant).

      https://spaceplace.nasa.gov/what-is-gravity/en/
      https://cosmosmagazine.com/physics/explainer-what-is-gravity
      https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question30.html

    • Photo: Matt Bawn

      Matt Bawn answered on 12 Mar 2018:

      Hi Jack,

      Gemma and Stéphane have given you excellent explanations of Newtons definition of gravity. Einstein had some problems with this though from his experiments on light may be this is interesting for you:

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