Sink or Float?

In the classes you took to learn to scuba dive, there was a lot of discussion about DENSITY and BUOYANCY. This might have some connection to this sunken ship. However, you don't remember all of the details. It's time to refresh your memory on these topics. To find out what DENSITY is go to this source:Density Fact Sheet.

Note in your Company LogBook what you find out. Buoyancy is an even more complicated subject! Go to Buoyancy Information to find out much more about this interesting subject.

Just to get a better and clearer understanding of what DENSITY really is you should go to a special site on the internet which has a related activity to do, called You will need to get a plug-in called Macromedia Shockwave in order to do this activity! Use only the equipment at the top of the page . Since you don't need it for your task, you can ignore the instructions at the bottom of the page. Use this link to a DENSITY TABLEincluded at our site to show your results and, if appropriate, you can then print out your results from that table.

You can also write in your results into the Company LogBook as well, answering this question: What general statement can be made from the data you have gathered regarding the density of objects in water or a liquid?

This activity may explain why some things float and others sink in water. But WHY did the ship NOT sink until it got well into the river, after barely floating in the ocean SALT water? You know that FRESH WATER has a density = 1 (gm/ml) You also know that SALT water is more dense than FRESH water.

How might this information account for the fact that the ship sank? Return to the density site at and change the density of the liquid in the pail . Look at and investigate how this affects the floating of rectangular or other objects.

Now what can you say about how a change in the density of water affects an object of a certain density when it is put into it? Write a statement into your LogBook.

How might this have accounted for the fact that the ship sank when it left the ocean and entered the river? What happened to the density of the water?
Well,you may be feeling pretty good about your research, and its about time to go scuba diving for the afternoon, before you head for the airport and that salvage operation. But when you descibe what you've learned, your companion asks you a related question which temporarily stumps you: "Why does a STEEL ship float even though it's more dense that either fresh OR salt water?"

Again you head to the web and search on some ideas. You find some help at Reeko's Mad Science Lab, where you can try an experiment to show your companion. Of course this raises some more questions for both you AND your companion: "How do ships today know how full to safely load a ship?" You may know something about this,even that ships are marked with lines called Plimsoll Marks or Lines, but after a search on the web you want to show your friend, so you go to both Plimsoll Fact Sheet or to refresh your memory. These sites show how both seasonal and salinity affects buoyancy of boats. Write down a few notes into your LogBook after your visit!

There is even an activity you might try with a ping pong ball and washers to achieve what is called "neutral buoyancy" at the Underwater Diving Physics site. And, if you want to check out ocean water density research already available you can go to: Bodega Bay Marine Lab. There are other sites listed in the Background Pages for you to check out as you wish.


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Sink or Float?


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