Reg Kehoe and his marimba queens

This one is a special treat...no educational content except the observation that marimbas are usually made of wood!

The bars for the lowest pitched notes are wider and longer, and gradually get thinner and shorter as the notes get higher.

Like the bars of a xylophone, the bars of a marimba are most commonly made from rosewood, but they can also be made from padouk and various synthetic materials.

Rosewood is the name given to a number of different timbers which have a rich dark red colour and a sweet smell. They are heavy and have strong resonance making them good for musical instruments. Unfortunately, many rosewoods, like Brazilian rosewood (Dalbergia nigra), are endangered due to over exploitation and should not be used.

The story of a forest ranger

This is another film from the excellent Prelinger Archive. This one was made in 1954 and looks at the job of the forest ranger in the USA. Again, you might recognise parts we used for our own videos.

Notice how the forests are talked about as a resource...but also how emphasis is placed on sustainable forestry and protection of the environment...even back in the 50s! Notice also how they stress the importance of avoiding forest fires. Back then many people smoked and lots of fires were started accidentally. Forest fires are still a big issue...all over the world (the UK included).

Wood for war - wood for peace

Ironically, the fact that we now have so many well managed forests in the UK is down, in part, to two of the most destructive events of the 20th Century: the two world wars.

During the First World War (1914 to 1918) Britain had great difficulty meeting the demands on timber - particularly for coal production and trench warfare. Britain's forests had been on the decline since medieval times and had been put under enormous pressure by the industrial revolution. Timber had been imported in large quantities for hundreds of years, but the war meant this supply was no longer reliable.

In 1919 the Forestry Commission was created and charged with reforesting the country with the help of private foresters. The idea was to improve the productivity of the forests and to create a large reserve of wood that could be called on in times of emergency.

Such a time came only a couple of decades later with the Second World War (1939-1945). During the war, the Commission's forests produced nearly one and a half million cubic meters of wood and nearly ten times more came from private estates.

These were times of great social change too. The 'lumberjills' were the forestry equivalent of the land army girls, but they weren't just felling trees - they were planting too...and the forests have been growing in size ever since.

Over the last 40 years or so the Forestry Commission has included conservation, ecology, recreation and tourism within it's objectives...and that's why we have today's multipurpose forests.

This is a video from the Prelinger Archive that was made during the Second World War looking at the same things from the American perspective. You might recognise parts we used in our videos.

Trebuchets

Words cannot describe how much we love catapults. Some work because of the springiness of the wood (its elasticity) and some rely on its strength. The awesome trebuchet is in the second category.

Trebuchets work as huge levers. The short arm of the lever has a large counterweight on it and the longer arm has the projectile - which weighs a lot less. The potential energy of the counterweight is turned into kinetic energy of the small projectile. It's all in the physics - the bread and butter for engineers.

Warwick Castle has the world's largest. Check out their website with loads of historical facts and a flash game you can play.

If you're looking for a woodwork project why not try building your own mini trebuchet ...like these kids did. The cola bottle is so cool! (8 minutes in)

Be safe though...not like the 'eccentric' guy in the third video!

Pykrete

Pykrete is a frozen mixture of water and wood fibre. Normal ice has very little tensile strength - it's brittle and cracks easily. The wood fibre helps spread the stress and bind together the ice making it many many times stronger.

It seems like a strange curiosity...but these days it is common to mix wood fibre with other materials like plastic and glue to make "composite materials" with improved properties.