Technologies K–10 · Years 9–10

Timber beam deflection: flat against on edge

Engineering focus area (NSW Industrial Technology 7–10, 2019); Design and Technologies: Knowledge and understanding, Technologies context: Materials and technologies specialisations (ACARA v9)

Practical, model not builtLow risk

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The idea

A beam's sag under a centre load is F L³ ÷ (48 E I), and turning a rectangular section on edge increases I by the square of the depth ratio, so the same timber sags almost 5 times less on edge.

What you need

1 length of 42 mm × 19 mm dressed pine, 1000 mm long
2 rounded supports 900 mm apart, fixed to the bench
Load hanger and 1 kg masses (4)
Dial indicator reading to 0.01 mm on a magnetic base
Vernier caliper

How to do it

Measure the real width and depth of the timber with the caliper (dressed sizes vary).
Lay the timber flat (19 mm vertical) across the supports and zero the dial indicator at mid-span.
Hang 1, 2, 3 and 4 kg at mid-span, recording the deflection each time, then unload and check it returns to zero.
Turn the timber on edge (42 mm vertical) and repeat.
Plot deflection against load for both, find each gradient, and work out E from the flat test: E = F L³ ÷ (48 δ I).
Compare the flat-to-edge ratio with (42 ÷ 19)² and compare E with the MGP10 figure.

What you should see

Taking E = 10,000 MPa (the rounded characteristic modulus that MGP10 names), the flat beam sags 0.62, 1.24, 1.86 and 2.48 mm under 1 to 4 kg, and on edge 0.127, 0.254, 0.381 and 0.508 mm. The ratio is (42 ÷ 19)² = 4.89 whatever E is, because I is 24,006.5 mm⁴ flat and 117,306 mm⁴ on edge. The deflection graphs are straight lines through the origin and the beam returns to zero when unloaded, showing elastic behaviour. The learner's E may differ from 10,000 MPa because a dressed pine stick is not a graded MGP10 member. The learner knows it worked when the measured ratio is close to 4.89 and the flat test gives a single, sensible E.

What changes

What you change: orientation (flat or on edge) and load (1 to 4 kg)
What you measure: mid-span deflection (mm)
What you keep the same: the same timber
900 mm span
load at mid-span
the same dial indicator position

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

A beam on edge is stronger because it has more timber (it has the same timber, arranged deeper).
Deflection doubles when the span doubles (it rises eight times, with span cubed).
Timber of one size always has one stiffness (it varies between pieces, which is why grading exists).

Safety card

Low riskLearners carry it out

Hazards

Masses falling onto feet
Timber springing off supports

Controls

Load gently and keep feet clear
Supports fixed and timber centred

Note

No chemicals or heat. Record the activity on RiskAssess (riskassess.com.au).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Industrial Technology 7–10 Syllabus (2019), NESA. Current; its Engineering courses are not available after December 2028. Code read from the official syllabus document (DOCX) on 2026-09-22.IND5-4 IND5-7
Engineering Technology 7–10 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the outcomes page on 2026-09-22.EGT5-MEA-01 EGT5-USE-01
Australian Curriculum v9AC9TDE10K06AC9TDE10P03

Sources

The pages the author read to write this activity.

All Concept Studio activities