Can Gravity Be Manipulated in a Science Fair Project?

[kakashi1027]

Hi,

I am currently thinking of a topic for my science fair project, and I was thinking about calculating the effect of gravity between two masses. The first mass(most likely lead or some other dense material) will be taped/glued to an bar with minimal mass, such as styrofoam or thin plastic so it will have minimal effect on the result. The bar will then be suspended from the roof of an box with a string. Then two pieces of lead far bigger than the ones suspended will be placed at the same height at a specific distance from the bar.


Theoretically, the x-forces and the y-forces are two differnt forces, and they don't affect each other, so Earth's gravity shouldn't affect this experiment at all. To remove the constant motion caused after the initial gravitational force, a dampener will be placed, which will most likely be a pad dipped in water to dampen the motion so only gravity affects it.


The independent variables will most likely be the density of the two masses, the ratio of the two masses, and the distance between the masses. The dependent variables will be the speed the first mass moves.


I would like to know if 1. if this is even possible, 2. if i should change some features to make it more interesting, and 3. If this overall would be a good experiment and is it original. i must do a project which is new and has not been done before.

 

[Danger]

I hate to come across as being a wet blanket, but I don't think that such an experiment can be undertaken with anything less than multi-million dollar measuring equipment. I don't know that you could call it "unique", but it certainly isn't done on a daily basis. If you can pull it off on a budget, it'll be a show-stopper.

 

[Lojzek]

This is a known old experiment for measuring G. I have seen the instrument at my college.

check http://en.wikipedia.org/wiki/Cavendish_experiment

However it is difficult to perform properly, because gravitation forces are so small.
You have made a mistake with the assumption that there would be no forces opposing movement (appart from force of dampener). First there will be friction forces and air resistance and secondly the string will resist torsion with a tiny torque, since a torsion requires stretching of the outside layers. This torque is most usefull for measuring force because it is independent of speed, so you can calculate force from the equilibrium distance to which the suspended mases move. This is basicaly a weighing machine with very small
friction and very small force/displacement quotient.

You certainly won't be able to construct this instrument yourself, because the required accuracy is too high. However you could find a school/colledge that has this apparatus and ask if they permit you to make a measurement.

 

[Danger]

I stand corrected. Thanks for the info, Lojzek. I honestly didn't think that anything so simple could measure something to that degree of accuracy.

 

[kakashi1027]

Hi, thanks for the replys.
If I were to get in hold of the instrument, is there anything that I can change to make this project "stand out" from other projects?
thanks!

 

[fss]

If I were to get in hold of the instrument, is there anything that I can change to make this project "stand out" from other projects?
thanks!

That you'd even be able to pull it off would be quite a feat.

 

[pervect]

Apparently it is possible, though difficult, to build a home-brew version. http://www.sas.org/tcs/weeklyIssues_2005/2005-07-01/feature1/index.html

I'm not sure what one could reasonable substitute for the toxic lead.

 

[JaredJames]

I did a similar project in school.

We used a pendulum and measured it's period. Once we had that we could use it to calculate g.

We could then 'prove' the mass of the Earth to show our measured value is correct.

Not quite the same, but along the same lines and far simpler to do. Same end result.

 

[kakashi1027]

Hi, I found another project done at home, so its not "impossible" to do at home.
http://www.fourmilab.ch/gravitation/foobar/

and I was wondering if that instrument Lojzek was talking about is common among colleges, and if there are any colleges in the Los Angeles area with that instrument.
Thanks again!