• Question: do you think it is possible that the gravity on earth will weaken?

    Asked by dillonlancaster to Cesar, Emily, Jamie, Kate, Philippa on 20 Jun 2011.
    • Photo: Cesar Lopez-Monsalvo

      Cesar Lopez-Monsalvo answered on 15 Jun 2011:

      No, unless the planet suddenly loses a massive chunk. The gravitational pull of the earth, and any other object, depends only on its mass. If for some reason the earth loses a significant proportion of it, then yes. But that would also alter its orbit around the sun, and certainly not many creatures in the planet would survive such an event. The only way that can happen, though, is if a huge massive object hits the earth. Of course if there would be such a threat we would know by now since such an object would be very very big ….so no need to worry about.

    • Photo: Kate Clancy

      Kate Clancy answered on 16 Jun 2011:

      Right on, Cesar!

    • Photo: Jamie Gallagher

      Jamie Gallagher answered on 19 Jun 2011:

      Hi Dillon,
      Did you know there are actually parts of the earth that have slightly weaker gravity. Gravity decreases the further from the centre of the earth you get. So if you go up to mount everest you will find that gravity is just a slightly smaller!

      And here is another amazing thing- most people thing that astronauts have escaped the earths gravity- this isn’t true in most cases. They are simply in a free fall. Amazing!

    • Photo: Philippa Demonte

      Philippa Demonte answered on 20 Jun 2011:

      @Jamie It is true that the further away from the centre of the Earth you are, the weaker the gravity, BUT mountains have a greater mass beneath them which increases gravity. The two probably balance out.

      (My dissertation was on micro-gravity surveying for which you have to do a load of corrections such as for Earth tides and terrain before coming to a final relative value)

      @dillonlancaster As @Cesar says, it is unlikely that the gravity on Earth would weaken unless either its mass decreases, or it’s radius* increases.

      *The equation is: g = GM/(r^2) where g = gravity, G = gravitational constant, M = mass of the Earth, and r = the radius of the Earth. The Earth isn’t perfectly spherical – it bulges slightly at the equator, and obviously because of the tectonic plates moving, the surface of the Earth is expanding where the plates are moving apart such as in the middle of the Atlantic, but shortening where the plates are moving together such as around the Pacific ocean. For the purpose of this equation though we assume a constant radius.

      Sorry, I’ve gone a bit technical. @dillonlancaster let us know if there is anything you don’t understand.