Welcome to science buddies. This is a very interesting experiment and one that is very relevant today.
Maryum wrote:1 How can i improve my experiment.
In my little bit of research, I found that by using egg shells, you used a good substitute for tooth enamel, the thin coating over the crown of the tooth (made up mostly of calcium). This of course protects the tooth from damage. If you have access to a microscope, you could examine the surface of the shells microscopically to compare any damage beyond discoloration. Stains and discoloration can sometimes be removed from the enamel, but because the enamel isn't made up of living cells, any physical damage is permanent. If you discover surface erosion of the shell due to contact with your solutions, this could be used to support any conclusions as to which beverage is worse for your teeth. Your school may have a microscope that they can let you borrow or use. If not, a cheap one can usually be found on line or at your local hobby shop and/or at Toys-R-Us. It would be helpful for your display board if you could get pictures of the magnified shell surfaces. For this, a USB digital microscope that would plug directly into a computer might be helpful.
Maryum wrote:2 i also measure ph of all the beverages on 3rd day of my experiment.
It is good that you took a pH reading. It is exposure to acids that tend to erode the enamel. If able, I would suggest taking several readings throughout the experiment (i.e. at the start, and then every other day until the end). This would allow you to draw some conclusions as to the reaction of the shell material and the acid in the liquids. I would expect the liquid to become more and more basic (less acidic) as calcium is dissolved from the surface of the shell and it leaches into the liquid.
Maryum wrote:3 What else can i do. how can i measure the hardness of egg shell.
For a follow-on experiment, you might take your results from this experiment and pick the 1 or 2 worst liquids for damaging the shells and see what effect brushing with toothpaste has on preventing/limiting that damage over a certain amount of time.
For measuring the hardness of the egg shell, you could find how much force it takes to break an egg by taking a fresh egg (one not exposed to any substance) and slowly increase weight on top of it until it breaks. I would suggest starting with something small like 5 ounces and then increase by one once at a time until the shell breaks. Record how much weight it took before the shell broke. Do this with several eggs (at least 3-5) and take the average weight. Use this value as the normal amount of force needed to break an egg. Then do the same thing with your test eggs by slowly increase weight until they break. See if it took more or less force to break than the normal amount, and by how much? If significantly less, then it would be reasonable to say that the acid in your test liquids made the shells weaker which would correspond to thinner and weaker tooth enamel.
I hope this helps.
"As the circle of light increases, so does the circumference of darkness around it."
~ Albert Einstein