Bouyancy and Row Boats
As one of our first field trips the Blue Band went to the aquatic park to learn how to both row and build a boat. It was a beautiful day to be out on the water.
Excited by the experience of rowing in the bay the band was a buzz with aspirations of building their own boat. Before diving into that ambitious project we had to better understand why things float.
"What are the qualities of something that floats?" This is the question that launched the Blue Band into an exploration of buoyancy. To answer this question our intrepid young scientists have rolled up their sleeves, formed hypothesis, tested those hypothesis and of course gotten wet in the process.
The first experiment: Will it float? The Blue Band found objects around the school to drop into water. First they made their predictions about whether the object would float and why then they tested their objects. There were some surprising findings. Despite predictions, a heavy paintbrush, whose bristles were cased in metal, actually floated. My heavy thermos that is made of metal also floated. These surprises helped the young scientists revise their definition of what floats. They had discovered that there were three important variables: size, weight and shape.
In our next experiment we endeavored to find out if there is a relationship between size and weight. We had been using graphs to find patterns in data so we decided to collect and graph some measurements. In four teams of two the students weighed bags of wood, ceramic, PVC and steel. Then, using the Archimedes principal of displacement, they figured out the volume of each material.
They graphed these points and discovered that their data points formed a rough line. Upon discovering this relationship we put a name to it: Density. Things that are small and heavy are more dense than things that are big and light.
Interpreting the graph the students discovered that the wood was less dense than the water, where as the PVC, steel and ceramic were more dense. The wood was the only material that floated! One of the qualities of something that floats is that it is less dense than water.
"If steel sinks, why can a ship made from steel float?" Next the young scientists looked at how shape effects an object's ability to float. They were given a lump of clay that sunk and were asked to create a shape that could float.
Next they were given tin foil and challenged to make a vessel that could float the most pennies. They made two iterations and graphed their findings.
To bring together all of our explorations, the Blue Band watched everyone's favorite mad scientist, Bill Nye, explain buoyancy to us. Bill's message: Things float when the water they displace is greater than or equal to the weight of the thing. This time the blue band designed their own experiment to test this claim. They decided to fill beakers to the brim with water, drop objects in to the water and compare the weight of the water that splashes out with the object. They discovered that the things that sunk weighed more than the water that was displaced and the things that floated weighed equal to or less than the water displaced.
Equipped with a better understanding of buoyancy, the blue band has a new challenge in front of them! They are building boats from cardboard and plastic that will float at least one person.