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Diagram 1 & 2,

Purpose:

To measure the density of different species of woods.

Apparatus:

• a large graduated cylinder or a 2 litre pop bottle with the top cut off (leave a narrow opening)

• ruler with millimetre scale

• electronic balance

Materials:

three 20-30 cm. strips of wood (fir, cedar, spruce); use the broken wood strips from Lab #2

Hook:

Ask the students:
Which wood sample do you think will be most dense? least dense?

Note:Density is the mass contained in a unit volume of a material. (g/cm³)

Dense woods usually shrink or swell more and usually present problems when drying lumber.

Procedure:

Mass/Volume Method:

-weigh each sample of wood (grams)

-find the volume of each sample of wood.

• Volume (cm³) = thickness (cm) x width (cm) x length(cm)

  -Density = grams/cm³

Flotation Method:

• The relationship of the length of wood immersed to the total length is an approximate measure of density. (See diagram)

  -take 1 x 2 x 20cm. strips of wood & mark each length into 10 equal parts (0.1, 0.2, 0.3.......1.0)

  -gently lower the wood strip into the cylinder that is 3/4 full of water THE STRIP OF WOOD MUST BE VERTICAL.

  - read the stick to find the water-immersion point

  -carefully withdraw the stick and mark the water line

  -repeat experiment for each wood sample

1) What is the density of each strip for each method?

2) How did the results from the 2 methods compare? If there are differences, why?

3) How did the density of each wood compare with its strength as found in Lab #2.

4) Wood density affects: strength, stiffness, shrinkage, swelling, nailing, resistance, wood machining, acoustical, electrical, and other wood properties. Can you think of times when you would want to use a dense wood? When might you want to use a wood of lower density?