• Question: If you make like a giant spaceship with enormous power to push and you take it to the moon can you push the moon or is it fixed in one place?

    Asked by humzaa to Daniel, Jon, Louise, Sharon, Zoe on 18 Jun 2010 in Categories: .
    • Photo: Jon Copley

      Jon Copley answered on 16 Jun 2010:

      Hell yes. On September 13th, 1999, there was a huge explosion of radioactive waste stored on the dark side of the Moon, and it knocked the Moon out of its orbit, and out of the solar system. The inhabitants of Moonbase Alpha then spent years wandering the cosmos getting into all kinds of scrapes with alien civilisations, most of whom seemed to include the actor Brian Blessed.

      At least, that’s what happened in the 1970s TV series “Space 1999” – http://en.wikipedia.org/wiki/Space_1999 – which I used to watch when I was little.

      Seriously though, if you have something that can push the Moon hard enough, then yes, you could move it. And if you did push it out of orbit, I think it would be pretty catastrophic for the Earth. Tides, most of which are caused by the motion of the Earth-Moon system, actually affect the solid rock of the Earth, not just the water sloshing around in the oceans.

      Fortunately, moving the Moon would require a huge force, such as getting hit by a wandering planet coming into our Solar System – and that would probably smash the Moon into bits rather than move it. But the Moon is actually getting further away from the Earth all the time, at a rate of about 3.8 centimetres per year. Scientists have measured this by bouncing lasers off the Moon.

      At the same time, the Earth is also slowing down in its spin, so that each day is getting about 2 milliseconds longer every century. Both those changes are happening because energy is being lost from the Earth-Moon system by friction from tides. And the first person to figure out that this must be happening was Charles Darwin’s son, George.

    • Photo: Louise Dash

      Louise Dash answered on 16 Jun 2010:

      Fun question! The answer is yes, but the explanation is quite involved!

      I don’t know if you’ve done Newton’s laws of motion in physics, but they are the answer to this question. In order to move anything, a mug of coffee, a spaceship, or the moon, you have to exert a force on it. Newton’s second law says that the force on an object is equal to its mass times its acceleration (F = ma).

      Meanwhile Newton’s third law says that “to every action there is an equal and opposite reaction” – meaning that if you push on something it pushes back! (example – you push down on the ground just by standing on it, and the reason you don’t fall through to Australia is because the earth pushes back.)

      So if you have your spaceship on the moon and blast off, you push against the moon and exert a force on it as you accelerate away. This force is equal to the mass of the spaceship times the acceleration, and the moon pushes back with the same force. Now, if you only have a small spaceship, its mass will be small and so will the force. The same force is pushing back from the moon, which has a HUGE mass, and so the acceleration the moon feels because of the spaceship blasting off is tiny, imperceptible in fact (but still there – so technically the Apollo moon landings moved the moon!)

      But if you have a spaceship that’s so big that its mass is similar to that of the moon, the acceleration of the moon will also be similar to that of the spaceship, and it will move quite a lot, and change the orbit of the moon!

      If you understood that – then well done! It’s the kind of thing we teach to physics undergraduates and even they have difficulties with it! (and actually I found it very difficult to explain too without confusing myself 😉

    • Photo: Sharon Sneddon

      Sharon Sneddon answered on 16 Jun 2010:

      I think I’ll leave this question to the other scientists, they seem to have answered it much better than I could!!!

    • Photo: Zoe Duck

      Zoe Duck answered on 18 Jun 2010:

      Don’t know! I’m definitely learning stuff this week 🙂