Page 40 - FOUNDATIONS FOR LIFE; EXPLORING GOD’S UNIVERSE

Science Y5 – God’s Amazing Matters – lesson 3-5
do not weaken it. Sound knots which occur in the central portion one-fourth the height of the beam
from either edge are not serious defects.

Water content

Water occurs in living wood in three conditions, namely: (1) in the cell walls, (2) in the protoplasmic
contents of the cells, and (3) as free water in the cell cavities and spaces. In heartwood it occurs

only in the first and last forms. Wood that is thoroughly air-dried retains from 8-16% of water in the
cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small
percentage of moisture, but for all except chemical purposes, may be considered absolutely dry.

The general effect of the water content upon the wood substance is to render it softer and more
pliable. A similar effect of common observation is in the softening action of water on paper or cloth.

Within certain limits the greater the water content the greater its softening effect.

Drying produces a decided increase in the strength of wood, particularly in small specimens. An
extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a
permanent load four times as great as that which a green block of the same size will support.

WE GET A LOT MORE FROM TREES THAN WOOD AND PAPER!
Did you know that trees provide us with more than 5,000 products that people use every day? It's true! From
photographic film to paints and from toothpaste to tyres, tree-based chemicals and other wood by-products
are all around us.

Resin
Wood resin is one of many tree-based chemicals. In nature, resin forms a protective coating around a plant
wound. It creates a hard coating that micro-organisms and insects can't penetrate. People gather the resin of
pine trees and use it in many ways.

Rosin is the most important of the hard resins. It is used in paint, varnishes, and in soap-making. Rosin also is
used to make the bows of stringed instruments sticky so they produce more beautiful music. And rosin is used
by ballplayers to give them a better grip on balls and bats.

Turpentine is the most widely used oleoresin. It is a solvent -- meaning that it dissolves other substances --
that is used in paint, varnish, waterproofing, and shoe polish.

Gum Resins are used to make other chemical products.

There are tree-based chemicals in many of our food and beverage products! Some of these chemicals are used
as flavourings, while others keep the ingredients in food from separating. There's even a tree-based chemical
that makes bubble gum chewier!

Cellulose, the material that makes up the walls of tree cells, is used as a food thickener in such tasty treats as
snack food, milk shakes, ice cream, cake frosting, and pancake syrup!

Cellulose also is an important ingredient in non-edible products such as eyeglass frames, steering wheels,
hairbrush handles, cellophane, and photographic film!

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