Bulldozer

The bulldozer is a very powerful crawler that is  equipped with a blade. The term bulldozer is often used to mean any type of heavy machinery, although the term actually refers to a tractor that is fitted with a dozer blade.

Often times, bulldozers are large and extremely powerful tracked vehicles.  The tracks give them amazing ground mobility and hold through very rough terrain. Wide tracks on the other hand, help to distribute the weight of the dozer over large areas, therefore preventing it from sinking into sandy or muddy ground. 

Bulldozers have great ground hold and a torque divider that's designed to convert the power of the engine into dragging ability, which allows it to use its own weight to push heavy objects and even remove things from the ground.  Take the Caterpillar D9 for example, it can easily tow tanks that weight more than 70 tons.  Due to these attributes,  bulldozers are used to clear obstacles, shrubbery, and remains of structures and buildings.

The Blade
The blade on a bulldozer is the heavy piece of metal plate that is installed on the front.  The blade pushes things around.  Normally, the blade comes in 3 varieties:

1. A straight blade that is short and has no lateral curve, no side wings, and can be used  only for fine grading.
2. A universal blade, or U blade, which istall and very curved, and features large side wings to carry more material around.
3. A combination blade that is shorter, offers less curvature, and smaller side wings.

Modifications
Over time, bulldozers have been modified to evolve into new machines that are capable of things the original bulldozers weren't.  A good example is  that loader tractors were created by removing the blade and substituting a large volume bucket and hydraulic arms which will raise and lower the bucket, therefore making it useful for scooping up the earth and loading it into trucks.

Other modifications to the original bulldozer include making it smaller to where it can operate in small working areas where movement is very limited, such as mining caves and tunnels.  Very small bulldozers are known as calfdozers.The skid steer has dozer blade which may be a viable alternative to a full on bulldozer