The chemistry of wood

This video is all about the chemistry of wood - and contains a lot of cutting edge science. The structures in wood that help determine its properties are tiny - it its only recently that technology has developed to the point were we can measure them and work out what they do. The work means chemists, engineers and foresters working together. This video is also available on the firrs DVD.



Here's another short wood science video that mentions cellulose and lignin - this one is from the History Channel.

Interactive physics (Phun)

There are a few interactive physics games out there, but this one is really excellent. You can read about it and download a beta version of the software at http://www.phun.at/. You can build all sorts of machines and structures.

why wood : what wood

Last week I gave a presentation it the Institute of Materials, Minerals and Mining in London, which was part of their Materials and Design Exchange (MADE). This was intended as an introduction to wood as a material and used some of the videos made for the firrs project. You can download a pdf copy of my presentation, with a few notes on what I said, here.

Social science

As well as the natural sciences, like biology, chemistry and physics, forestry involves the social sciences - the study of human behaviour and society. Forests provide many important benefits to people and communities.

Social forestry is the study of things like:

• How people interact with forests
• How foresters can improve engagement with local communities
• How forests support employment and rural economies
• How forests contribute to health and wellbeing

As a public body, the Forestry Commission has been particularly active in this area, but private forestry companies also make use of social forestry.

Forestry, timber and climate change

Forests and climate change are very closely linked, but in ways that are not generally well understood by the public. The science is complex and interconnected and often you hear only one side of the story. Fortunately the Forestry Commission has recently released a video that covers the subject in a very clear and balanced way. It also tackles a few widely believed myths too. I challenge you to watch it and see if it doesn't tell you something that surprises you.

The reality is that human impact on forests is both a problem and a solution - and that we need science to tell us what the consequences of our actions are. If you are thinking of a science or engineering based career that helps save the planet you couldn't do much better than working in the forestry and timber.

Forests are vast sinks of the greenhouse gas CO2 but they offer so much more - from renewable energy to low carbon building materials...just so long as they are sustainably managed. The challenge for foresters is to use science to understand both the effect of forestry on climate change ...and the effect of climate change on forestry.

You can download a high quality copy of the video at the Forestry Commission's website: http://www.forestry.gov.uk/forestry/INFD-6umkar

The science of sound

Here we have a couple more films from the Prelinger Archive. The first from 1933 and the second made in 1948...back when a scrap of wood on a piece of string was carried by every child.

These videos explain the science of sound...what it is and how it's made. This will help you understand our video "measuring stiffness with sound".

Measuring stiffness with sound

It is very useful to know the engineering properties of the timber in logs before they are sent to the sawmill. Time and energy spent sawing up a log and kiln drying the battens is wasted if that timber later fails to meet the grade for construction. It would be much better to put that log to another use.

The science of sound allows us to do just that. The speed of sound through any material is related to the material's stiffness. In fact, stiffness equals density times the speed of sound squared.

That means if we can measure the speed of sound and the density we can calculate stiffness.

To do this we measure how long it takes the sound to travel from one end of the piece of timber to the other. Then it’s simply a case of speed equals distance divided by time. To explore the science further why not look at our whack-a-stick simulation or read about our exhibit at the Royal Society Summer Science Fair 2007?



This was one of the first videos we made. Annie and Heraa had just started their Nuffield Science Bursaries and we were practicing using the video camera. It just so happened that on the day, Peter Carter from Fibregen was visiting the laboratory to talk about his acoustic testing tool with John and Andy from the SIRT project.

We decided it was a good opportunity to make a short video, so Annie and Heraa asked Peter how it worked and we videoed Annie doing a demonstration.

This tool, the HM200, is called the Director, but people also call it the "Hitman". It is designed to work in busy, noisy timber yards but in the quiet of your own home or classroom you can make your own "non-destructive acoustic testing device". All you need is a microphone and a computer with some software that will analyse the frequency of sound. We have found that the free software called Audacity can do this well enough for a demonstration.

When you hit the end of the wooden batten with a hammer, the main sound you can hear is the sound of the first mode of resonance. The frequency of the first mode of resonance is the time it takes the sound to travel along the batten, bounce off the end and travel back down the length of the batten. This means the wavelength of the first mode of resonance is twice the length of the batten.

It sounds complicated at first, but it’s actually quite simple. All you need to do is hit the piece of timber and analyse the sound to find out what frequency it was mainly made off. So long as everything is working as it should, that is your first mode frequency.

To calculate the speed of sound in the timber:

(Speed of sound) = (wavelength) x (frequency) = 2 x (batten length) x (frequency)

And to calculate stiffness:

(Stiffness) = (density) x (speed of sound) x (speed of sound)

Here is some proof that we did not fake anything for the video. We took the audio recorded from the video and opened it in Audacity (we've extracted the sound of the hammer strikes so you can do this yourself). We then selected the sound of the hammer strike and selected "plot spectrum" from the "analyze" menu.

What we want to look at is the frequency spectrum – that's the graph with frequency on the horizontal axis and the level on the vertical axis. The higher the level the more of that frequency there is in the sound.

The sound contains lots of different frequencies, but we are mainly interested in the highest peak. This is a frequency of 554 Hz.

And if we look at what the figure on the laptop in the video it says 558 Hz. Pretty close huh?



Did you notice the time on the laptop clock? We don't work that late! That was New Zealand time. The laptop was Peter's and that's where he lives.

Wood shrinkage

This is a delightfully retro video looking at the microstructure of pine wood and why it shrinks when it dries. It gets quite complicated with the terminology but has good visuals that help show how things work even if you don't understand the words. The things that look like air bubbles are meant to represent water droplets.

You might also want to look at our video about the chemistry of wood (on the firrs webpage).

Wood colour and chemistry

Here's a fun little video from the WoodWhisperer talking about how the colour of wood can change over time. This is all down to chemistry and something called oxidation. That's the same process that turns a sliced apple brown.

Sapwood is the outer part of the tree trunk - the wood that the tree is using to transport sap. The heartwood is the inner part of the tree trunk - the part of the wood that the tree uses to store waste chemicals...the extractives mentioned in this video.

As a tree ages the inner part of the sapwood slowly turns into heartwood. Heartwood provides structural support to the tree, but not much else and with very old trees it is common for the heartwood to be decayed away.

Different species of tree produce different extractive chemicals which explains why they can have such different colours.