DRY WOOD, WATER and SPECIFIC GRAVITY Catherine Christie Carabetta 7

TOPIC QUESTION: How does the density of wood affect how much water the wood will absorb?

HYPOTHESIS: Kiln Dried Wood: If lighter pieces of wood are less dense because they have lots of air pockets, then they will continue to float even after absorbing water.

ABSTRACT In the Experiment, I wanted to test which woods absorb enough water to sink. My dad helped me by cutting different kinds of kiln dried wood so each one was the same size and shape. We then put the pieces of wood into separate empty peanut butter jars and let them soak in water for two weeks. Of the eight samples I tested, three ended up absorbing enough water to cause them to sink. This was because the combined weight of the wood and the absorbed water made the wood weigh more than the water it displaced. Since I learned that the Specific Gravity of Water is one, the three pieces that sank had a Specific Gravity more than one and the 5 that remained floating had a Specific Gravity less than one.

MATERIALS: Experiment: 1. Eight pieces of different types of kiln dry wood 2. Saw, ruler 3. Eight empty peanut butter jars, cleaned and filled with water 4. Scale 5. Camera 6. Computer

VARIABLES: Manipulated: Type of wood Dependent: How much water the wood absorbs Controlled: Time soaking in Water of same temperature

STEP-BY-STEP PROCEDURES: Process 1.Find eight types of kiln dry wood. 2.Cut each wood piece to the same size and shape. (1/2” x 1” x 2”) 3.Fill eight empty peanut butter containers with water. 4.Weigh each piece separately and record its weight. 5.Put dry each piece in a container of water. 6. Take pictures of them in the containers. 7.Let them soak for two weeks. 8.Take pictures and record observations of any pieces that sink. 9.Take them out, shake off water, pat them dry and weigh immediately. 10.Record the new weights. 11.Summarize the data.

Process Steps

Observations: 1.One type of Wood sank immediately- this was Ipe’ which is one of the few woods with a Specific Gravity greater than 1 2.The other wood floated at different levels, some like Maple and Philippine Mahogany barely floated right at the surface. Others like pine, floated almost on top and others floated half way submerged. 3.Two of the pieces that floated just at the surface- Maple and Philippine Mahogany sank after 7 days and 13 days. 4.The other types of wood continued to float, but they all sank a little lower in the water than when they started.

Definition: Specific Gravity is the heaviness of a substance compared to the same amounnt of water. Specific Gravity of water is 1. Things that have a Specific Gravity less than 1 float, and things that have a Specific Gravity more than 1 sink. To figure the Specific Gravity of wood, float the block of wood in water and if 50% of the block sinks below the surface, it’s Specific Gravity is If it sinks 75% below the surface it’s Specific Gravity is Specific Gravity tells about the density of the wood.

DATA TABLE (Sorted by Specific Gravity) Block #Type of WoodNotes Dry Weight (oz) Water Weight (oz) Wet Weight (oz) Water as % of Wet Weight Specific Gravity Wet Weight (Oz) 2Cedar % Pine White % Honduras Mahogany % Yellow Pine % Red Oak % Philippine Mahoganysank day % Rock Maplesank day % Ipe'sank day %

GRAPH 1 – Weight and Percent of Water in Wet Weight

GRAPH 1 – Specific Gravity vs Weight Sank day 13 Sank day 7 Sank day 1 oz

GRAPH 1 – Specific Gravity vs Weight oz

RESULTS: Claim Wood that is less dense with a low specific gravity continues to float even after absorbing as much water as a denser piece of wood that eventually sinks. Evidence If you review that data table and graph, you will see that Rock Maple and Philippine Mahogany both absorbed.6 oz. of water, and they sank within two weeks. Red Oak also absorbed.6, but it did not sink- probably because the air pockets in the wood are not connected(?) and it never absorbed enough to weigh more than the water it was replacing. Yellow Pine and White Pine absorbed.5 oz. of water and did not sink. This is due to the lower specific gravity of these and the other woods.

CONCLUSION: Wood usually floats (except Ipe’!). When I was doing my research I found out this is because wood is like a sponge – it has air pockets mixed in with the wood fibers. Dense wood with high Specific Gravity has heavy, compact fibers. Light wood with low Specific Gravity has a light, loose cell structure. Light wood has lots of air pockets between the cells, and heavy types don’t have as many air pockets. Some types of wood have independent, sealed-off air pockets like bubble wrap, and some types have air pockets that are all connected and open like a sponge. How long wood floats before becoming water logged depends on the type of wood and its specific gravity as well as type of air pockets it has, and the amount of time spent in water.

APPLICATION These are just a few examples… Stuck on a deserted island - would you want a raft made out of Ipe, or one made out of pine? Building a deck- do you want posts that will absorb water? To make a fishing net would you want to use cork, or a wood that could get water-logged?

CITATIONS: Specific Gravity and Other Properties of Wood and Bark for 156 Tree Species found in North America, Research note NRS-38 by Patrick D. Miles and W. Brad Smith, 2009

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