A thought experiment involvng a large bridge
 

This one is inspired by large bridges, such as the Humber Bridges.

It is known that in real long bridges, they need to take into account the curvature of the Earth, so that the distance between the towers at the top is greater than the distance at the base of the towers.

Suppose you had a very long bridge and so the towers are built so that they are both tracing a line that leads to the centre of the Earth. (See attached diagram)

The bridge deck however is perfectly flat and frictionless. In fact it is parallel to a line through the centre of the Earth. It is perpendicular to the line from the centre of the Earth that bisects the angle the line of the bridge towers make at the centre of the Earth.

The Bridge deck is made of a fictional material that keeps it rigid and does not flex. Assume no issues with weather.

Again see diagram.

Now suppose we take two bowling balls, place one at a bridge tower and one at the centre of the bridge deck.

When the balls are released, will the ball at the tower roll, if so which direction. It is the same question with the one in the centre of the bridge deck. The one in the centre of the bridge deck, if it is placed slightly off centre in either direction towards either tower, what should happen.

Explain your reasoning.

I will wait before I give my thoughts.

:think:

the ball on the deck near the tower will roll toward the centre. It will roll past the centre and then like a pendulum arm slow down, momentary stop and then roll back to the centre. This will repeat infinitely since there's no friction and the distance it travels past the centre of the bridge will be equal to the the initial distance from the centre of the bridge. This is due to gravity and the centre of the deck being to closest point to the centre of the Earth. This answer assumes no Earth rotation which I'm guessing was implied. The other ball which is closer to the centre but is slightly off set will do the same but at a smaller scale.What's my prize biatch?

Physicist of the Week

Plus extra credit for spotting that the ball would behave like a pendulum, or as we say in mechanics, Simple Harmonic Motion :thumbs:

next time I go bowling on a bridge I'll be all set. :P

lol...what on earth?

nerdness... that's what, and I have the "Physicist of the Week" badge to prove it! :P

But nothing actually goes near the centre of the Earth in this set up.

What I put were construction lines.

For more discussion, I also posted this thought experiment on this forum which is a science based forum.

Apparently I just reworked an old concept.

awwww but those boffin never mentioned that the balls would keep moving like a pendulum nor did they mention the fact that the movement would occur infinitely since nowhere in the setup is energy being dissipated.

You could register there and go and tell them :wink:

nah... I already have my "Physicist of the Week" badge

Aw ange7 ruined it, hahaha. I was thinking about it but accidentally read the post.

I wouldn't have got it probably, physics is not my forté.

http://i427.photobucket.com/albums/p...heUniverse.jpg :P

On the other forum, they have pointed out I may have forgotten to take into account the rotation of the Earth.

If you look at the earlier link and go to that forum, you can see my additional bit to the scenario.

Just to keep it interesting

Yeah I beat them to it :P
"This answer assumes no Earth rotation which I'm guessing was implied." said ange7 ...
I'll check the link out. Cheers Sticks

:shocked: Wow i would never be able to get that