# Thread: Help with science project

1. As the title suggests, I need help with a science project I'm doing.
It's suppose to be a four-year project, and I"m about half way through year three. I've done the research, the proposal, and all that. Now, all I have to do is do the experiment, and present my data.

So, my experiment is comparing the surface area of an object to it's sinking speed in water. For example, does something with a big surface area sink faster or slower, etc, etc.

My problem is:
I need materials such that mass and density stays the same, but surface area changes. I'd have to go re-look up things about floating, but I can't remember if mass really matters all that much. But I know density does.

So, can I buy these anywhere? Are there any companies that would custom make these? Or is this even able to be done?

Thanks.

2.

3. Originally Posted by Mysel
My problem is:
I need materials such that mass and density stays the same, but surface area changes.
That would only be a single material, and the way you would change the surface area is by different shapes. A piece of clay with a spherical shape would have the minimum surface area. Mold the same piece of clay into a cube and it will have the same mass and density, but more surface. Etc.

4. If mass and density stay the same, then by definition volume stays the same, so you are really going to be measuring the drag coefficient of different shapes. You can have an infinite number of different shapes with the same surface area, so a correlation of surface area with sinking speed is meaningless unless you also include a shape factor.

An aluminum foundry might make you some inexpensive castings if you give them a wooden pattern to make the sand mold.

5. You ought to consider doing your experiments on 60/40 solder because of its high density and low melting point (about 370F or 186C). Solder is available in bar form: http://www.bertech.com/product1/solder_bar.htm and does not absorb water as clay would do.

Your problem really is to know the surface area of each sample you use. You might be able to melt the solder into molds of simple forms such as rectangular blocks, discs, and cylinders for easy surface area calculations.

Also, many lead fishing sinkers come already molded into spheres or pyramids. If suitable, that seems to be a cheap and easy way out. Check at sporting goods stores.

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