rationalskepticism.org

GapWim wrote:a YouTube video called "The earth is not rotating - spinning - or moving !!"
http://www.youtube.com/watch?v=xokMcO3T0SY
Unfortunately, with every attempt to educate the poster ... the comment gets blocked.

campermon wrote:

campermon wrote:

questioner121 wrote:

...I'm thinking on this one. I was thinking about the centripetal force acting on the earth to keep it going around the sun. Should they not affect the hovering object? Would there not be a difference in forces at noon and at midnight? During midday I'm assuming you'd have centripetal force of the sune acting to lift the hovering object higher and at midnight you'd have the centripetal force acting to pull the hovering object down.

I'll have a think about this...going to bed in a minute!

OK....a little bit of breakfast time beer mat physics and look at the centrifugal forces on a mass as it rotates on the planet and orbits the Sun..

Consider a mass at the equator on a rotating Earth. In the diagram we are above a pole and the Earth is rotating clockwise with a tangential speed v at the equator:



In the diagram:
R=distance to Sun from centre of the Earth
r=radius of the Earth
V=tangential speed of orbit around the Sun
v=tangential speed of rotation of the Earth

When the mass is closest to the Sun, we can write the centrifugal force as;

F1=m(V+v)2/(R-r)

and at its furthest;

F2=m(V-v)2/(R+r)

Lets look at the difference in force experienced by the mass at these two points;

ΔF=F1-F2=m(V+v)2/(R-r) - m(V-v)2/(R+r)

Let's make life easy and do the sums for a 1kg mass and using;

V=29800ms-1
v=470ms-1
R=150 000 000 000 000m
r=6 400 000m

We bung the numbers in and get;

ΔF=0.0004N

So, in answer to your question re: the hovering object; the Sun has an extremely small influence.