Question for the resident boffins.....

**Ixion** · 28th February 2006, 18:08

Schrodinger's cat

**MSTRS:Me** · 28th February 2006, 18:17

He a member here??? I was thinking of MidnightMike's and whether it has a name yet

**Jamezo** · 28th February 2006, 18:38

Originally Posted by TwoSeven

I dont believe you have used the right formula for your statements that went with it. But then I am not familiar really with that formula.

My question is that you stated that the motorcycle is accelerating towards the centre of the earth, but in your formula you give the value of 'r' as being the same. For something to accelerate towards the centre of something 'r' must get smaller.

As I understood newtons law, the wieght can only change if the distance from the centre of the earth changes, or another gravitational body pulls on it. So maybe it might weigh less on a full moon or something

Nope, anything that is not moving at a constant velocity is accelerating. The direction of this acceleration for an object moving in a circular fashion is tangential to the velocity, and directed towards the centre of the arc of motion.

Thus the bike accelerates towards the earth, as its velocity changes while travelling around the earth.

This is the acceleration which partially negates some of the weight force by 'allowing' the bike to accelerate in the same direction as gravity is trying to make the bike.

**scumdog** · 28th February 2006, 23:23

Originally Posted by MisterD

Thought experiment: Remove gravity, then get a rocket and fire it horizontally. It would travel at a tangent to the earth's surface and therefore appear to climb. Now reinstate gravity, the balance between it's pull towards the earth and the rockets velocity determines whether the curved path the rocket follows hits the earth, runs parallel to it (orbit) or spirals outwards.

True, true, BUT if you extended the rocket so it was 20km long you would find the nose was further away from the earth than the centre section, ergo it is actually pointing AWAY from the earth, in other words upwards, albeit at a very slight angle.
So there!

Oops about the 'find'