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 0.50. If it sinks 75% below the surface it’s Specific
Gravity is 0.75. Specific Gravity tells about the density of the wood.
DATA TABLE (Sorted by Specific Gravity)
Block
#
Type of Wood
Notes
Dry
Weight
(oz)
Water
Weight
(oz)
Wet
Weight
(oz)
Water as %
of Wet
Weight
Specific
Gravity
Wet
Weight
(Oz)
2
Cedar
0.5
0.3
0.8
38%
0.38
0.3
1
Pine White
0.7
0.5
1.2
42%
0.42
0.5
6
Honduras
Mahogany
0.8
0.4
1.2
33%
0.54
0.4
7
Yellow Pine
0.9
0.5
1.4
36%
0.54
0.5
3
Red Oak
1.1
0.6
1.7
35%
0.59
0.7
8
Philippine
Mahogany
sank day 7
1.0
0.6
1.6
38%
0.7
0.6
4
Rock Maple
sank day 13
1.1
0.7
1.8
39%
0.72
0.6
5
Ipe'
sank day 1
1.5
0.3
1.8
17%
1.08
0.3
GRAPH 1 – Weight and Percent of Water in Wet Weight
Sank Day 13
1.2
Sank Day 7
1.08
0.54
42%
0.42
38%
0.38
0.6
0.59
0.54
36%
33%
0.8
0.72
0.7
1
39%
38%
35%
0.4
17% 0.2
Water as % of Wet Weight
Ro
ck
M
Specific Gravity
Ip
e'
ap
le
y
M
ah
og
an
O
ak
Re
d
ne
Pi
Ye
llo
w
Ph
ilp
pi
ne
Ho
nd
ur
as
M
Pi
ne
ah
ho
ga
n
W
hi
te
y
0
Specific Gravity
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Ce
da
r
Ounces
Specifc Gravity vs Water Weight as Percent of Wet Weight
(after two weeks)
Sank Day 1
GRAPH 1 – Specific Gravity vs Weight
Weight of Wood and Water in Soaked piece
oz
Sank day 1
Sank day 13
2
Sank day 7
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Cedar
Pine White
Honduras
Mahhogany
Yellow Pine
Dry Weight (oz)
Red Oak
Philppine
Mahogany
Water Weight (Oz)
Rock Maple
Ipe'
GRAPH 1 – Specific Gravity vs Weight
Percents of Wood and Water in Soaked Piece
oz
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Cedar
Pine White
Honduras
Mahhogany
Yellow Pine
Dry Weight
Red Oak
Water Absorbed
Philppine
Mahogany
Rock Maple
Ipe'
Evidence
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.
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 sinkprobably 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:
1. www.windt-ed.org
2. www.bellforestproducts.com
3. www.reade.com
4. www.advantagelumber.com
5. www.technologystudent.com
6. www.tataenterprises.net
7. www.woodfinder.com
8. www.chacha.com
9. www.nrs.nf.fed.us 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
THE END