Cranes are force multiplying machines. That means that they take a small amount of force and then turn it into a larger force, allowing the crane to lift very heavy loads and put them where they belong. That's why they are found at all kinds of construction sites. They make it possible for the construction workers to get materials up to where they need to be. While all cranes do the same thing, there are different kinds of cranes that show up at construction sites.
These are portable cranes which are set on a heavy truck body. The truck tends to be counterweighted in the front so that lifting a load doesn't make the truck tip backward. They also tend to have outriggers. Outriggers are legs that spread out from the side of the truck and help to anchor the truck to the ground. That can also change the center of balance of the truck crane, keeping it steady while the crane does the work. Since truck cranes are generally smaller cranes, they can only handle small loads and can be found both at small sites or at larger sites to help stage loads for larger cranes to lift.
Boom cranes are larger than truck cranes, but smaller than tower cranes. They can lift heavier loads and get them up higher than a truck crane can. Boom cranes can lift things up several stories or even up over a multi-story house and deliver the load to the backyard. Boom cranes are generally just a cab with the crane and mounted on tracks. That makes them generally portable. They are good tools to use on sites that have rough terrain since the tracks get much better traction than wheels do. However, boom cranes usually aren't street legal. That means that to get the crane from one worksite to another, the crane will have to be loaded on a flatbed truck so that it can be moved. Larger boom cranes may count as oversized loads and the transport company may need to get a special license to transport the crane from one site to another since transporting the crane may interrupt traffic.
There are different kinds of cranes because there are so many different kinds of lifting jobs that need to be done. Truck cranes and boom cranes are just two of the cranes that can be seen on construction job sites. For more information, visit websites like http://winslowcrane.com.