Engineering World War I: How do tanks drive?

by Simon Jones

This year marks the centenary of the beginning of World War I so we’ve decide to look into some of the engineering advances developed during warfare.  We’ll also think about how these advances help us day to day, and how they link into some of the Key Stage 3 and 4 Science, and GCSE Engineering curricula.

a trebuchet

“You can call me Lord Bouldermort” Photo: Robbie C CC-BY-SA

Let’s start with some really old warfare engineering. In our Tomorrow’s Engineers show “Tomorrow’s Engineers: Around the World”, we have a model trebuchet, a medieval weapon of war; an application of physics which solves an engineering problem, namely how to exert large scale damage on protective castle walls by flinging heavy boulders at them. The trebuchet is a great symbol of a cornerstone of engineering – building devices that allow us to do something better than we can do by hand.

Often weapons are created on fairly straightforward concepts, with fantastic science and engineering at their heart. It is a sad truth that for all the horror and destruction a war may bring, it can often bring about defining advances in society, government, and attitudes to science, as well as providing useful scientific knowledge for designing many civil (everyday) objects.

 

Two fish are in a tank…

…one says to the other, do you know how to drive this thing? The story goes that the word ‘tank’ was a purposeful misnomer implying a water storage unit, a decoy name to disguise early prototypes from prying eyes. The tank had many objectives, from trampling barbed wire fences to crossing rocky terrain and firing shells, however I want to look at one engineering problem, and partial solution, which the tank helped develop.

Daddy_in_the_great_war

“Well young lady, I applied scientific principles to create new engineering solutions to problems in the world”. Image (Public Domain)

Attempting to drive a car across the grizzly mud of the battlefield would be futile, as the wheels would quickly become stuck in the mud. Tanks addressed this problem by replacing the idea of the wheel with large caterpillar tracks – somewhat literally reinventing the wheel.

The science behind tank tracks is fairly straightforward, it is all a balancing of forces. The reason vehicles get stuck in mud is because mud is slippery, and typical car wheels (designed for the road) can’t create a strong enough force, through friction, to push the car along. Instead, the wheels end up spinning. One successful solution to this is bigger wheels, such as the wheels used on some tractors. Bigger wheels mean a bigger surface area, and that means more contact between wheel and ground to push off from, and thus a greater force.

However big wheels have two problems in the case of trench warfare. The first, perhaps rather obviously, is that are easily prone to damage and being punctured. The second is that a tank is heavily armoured and very heavy, meaning gravity exerts a far greater force and even with their larger size, big wheels are still prone to sinking.

Engineers previously used caterpillar tracks on a few types of tractor. When designing tanks, we took a little-used engineering solution and applied it. Caterpillar tracks are wide and press against the ground in long strips. This spreads out the intense vehicle weight over a large area of ground to provide more friction whilst also avoid sinking. And it worked, for the most part, although tanks did still find themselves stuck in the mud fairly often, often leading to their capture…

tank tracks and wheels

Surface area matters. Image: science made simple (CC-BY-NC)

Curriculum Links:

Key Stage 3:

Physics (Forces): Friction between surfaces rubbing

Key Stage 4:

This science made simple blog intends to enrich, and give context to:

AQA GCSE Physics: P2.2.1 Forces and Energy d) Work done against frictional forces

AQA GCSE Engineering: Use the design process to generate ideas/possible design solutions for engineered products.


 

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Posted in Engineering, Physics