Date:  __________________           Name:  ___________________________

 

 

WOOD TECHNOLOGY LAB # 2

STRENGTH COMPARISONS OF VARIOUS WOOD SPECIES

 

Purpose:                          To measure the strength and stiffness of different species of wood.

 

Apparatus:            safety glasses

metre stick

                        1 litre container (plastic milk jug)

                        20 litre pail (with handle)

                        35cm x 35cm foam padding for floor (or carpet sample)

                       

Materials:      1cm x 2cm x 100cm wooden strips (western red cedar, pine/spruce, Douglas-fir/western larch)

                        water

                        toothpick

                       

Procedure:

-          measure and mark 10cm in from each end of each stick

-          measure and mark the center (50cm) point of each stick

-          place the stick on its wide face between 2 table tops so that the edge of each bench lines up with a 10cm mark on the stick

-          tape a toothpick near the center of the stick so that it juts out perpendicular to the stick and parallel to the ground

-          attach a piece of graph paper to a wall or back of a chair so that the toothpick almost touches the paper.  Mark zero point (no load) on graph paper.

-          hang the 20-litre pail from the center-point of the stick and record the deflection with the empty bucket. Place a foam-pad on the floor, under the pail to cushion the falling bucket (when the stick breaks).

-          fill the pail by slowly adding water in increments of 1 litre.  After each addition of water, note the deflection in the wood by marking the point on the hanging sheet of paper.  (ie. the position the toothpick points to).

-          wear safety glasses

-          continue slowly adding H2O IN 1 litre increments until the wood breaks

 

Observations:

 

-          use the data you collect while completing the experiment to fill in the following chart.  Place a “check mark” to indicate successful additions to the load and an * to indicate the approximate mass when the stick broke (rupture point).

 

LOAD (kg)	DEFLECTION (cm)
	Cedar	Pine/spruce	Fir/larch
i (no load)
with empty bucket
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

 

-          On page 3, graph the relationship between Load and Deflection using the three different symbols indicated above the graph:

 

 
GRAPH

THE RELATIONSHIP BETWEEN MASS AND FLEXIBILITY

CEDAR (X), PINE (l), AND FIR (u)

 

LOAD (kg)	25
	24
	23
	22
	21
	20
	19
	18
	17
	16
	15
	14
	13
	12
	11
	10
	9
	8
	7
	6
	5
	4
	3
	2
	1
		1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20

 

DEFLECTION (cm)

 

NOTE:  Plot each point from the chart and connect each species with a smooth curve.

On your graph, use an * to show the rupture point for each species.

 

Follow Up Questions:

 

1.      Which wood species is able to support the greatest mass? _____________________

 

2.      Use the graph to predict what the deflection would be if each species was supporting 6.5 kg of mass? 

 

cedar ___________  pine/spruce _____________ Douglas-fir/larch ______________

 

3.      If each species was deflected to 6.0 cm, what would be the mass supported?

 

cedar____________ pine/spruce _____________  Douglas-fir/larch_______________

 

4.      From the wood species you tested, choose the species you think is best suited for each of the following and explain why.

 

a)     flooring material:  _____________ because ____________________________

 

b)     diving board:  ________________ because ____________________________

 

Conclusion:

 

1.      Rank the species in order of strength and in order of elasticity.

 

strongest 1. __________,       2.  ______________,       3. ___________      weakest

most flex  1. __________,       2.  ______________.       3. ___________      least flex