With valuable data on the ocean floor, a submersible would need to venture to the bottom of the ocean.  It would then need to return to the surface of the water so that the ocean engineer could retrieve the information.  Knowing about density is important in making sure the data is able to be collected!  Therefore, a submersible needs to both sink AND float!

Testing various instruments, second graders are discovering that density is a key factor in getting something to sink and float.   Every time they added a new instrument to their submersible it changed the overall mass and volume, and therefore, density.  

Since second graders have learned what the specific parts of a submersible can do in regards to collecting data (think how much salt is in the water, the temperature of the water, or a manipulator arm to gather data!), they are exploring how these instruments, which are all packed differently, interact with the water.   

Some are packed with sand, others with marbles, and others with pony beads.  Not only is their mass different, but so is the volume of each instrument.  These factors affect the instrument's density, and therefore, the amount of water they displace.  Ultimately, this determines whether something will sink or float.  Taking all this into consideration, second graders are thinking about a real problem an ocean engineer might face...how would you get a floating submersible to sink down to the ocean floor to collect data?  And how would that sunken submersible be able to return to the surface and float once it got the data it needed?  Hmmm....what a problem to have!

Density is a physical property of matter.  It is also a mathematical relationship that exists between mass and volume.  Just because something has a large mass doesn't mean it will sink.  And just because something is lightweight doesn't mean it will float!  

Whether something sinks or floats also depends on its density.  In second grade terms, density describes how packed a material is.  The more it is packed, the more mass has been crammed into a specific volume.  Increase the volume, and the mass has more room to move around and is therefore less dense.  Since ocean engineers design technologies that need to sink and float, being able to manipulate these factors is

In their introductory lesson on sinking and floating, second graders were given the challenge to get three film canisters to sink, float, or stay suspended in a cup of water.  Using only washers, they experimented with changing the film canister's contents to reach the goal.

Some students hypothesized that heavier things sink and lighter things float.  Is this always true?  As we dig deeper into ocean engineering, we'll either prove or disprove this claim!