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Crane Science Explained Simply

Chances are, you’ve got an interest in cranes or crane hire. You might even work in construction and be familiar with the principles of crane operation, but not many people understand the interplay of forces that are required to design and use a crane effectively. Words like torque, fulcrum and pulley may seem intimidating, but when using a crane on your next project or even thinking about operating one yourself, it’s great to have a grasp on the basic science. Cranes are amazing pieces of machinery that reflect an incredible use of physics and mechanical engineering. If you’ve been involved in a construction project before, you’ll know how difficult it is to manoeuvre loads and beams without some kind of support. Request a mobile crane enquiry to demonstrate some of the theory engaged in this piece on your next job site by contacting St George Cranes.




Cranes are easier to understand once they are analysed piece by piece. The jib is the arm that conducts the lifting, which somehow stays balanced no matter how heavy the load. This is due to a counterweight that is applied to the other end. This changes based on the load being lifted, either by changing the weight, or changing the distance between the weight and the load. Imagine 2 children on a see saw, where one is heavier and un-balances the other child. The heavier one then sits closer to the balancing point of the see-saw – where the equipment sits on its base. In crane speak, this is called the fulcrum. Each child is now an equal distance off the floor because the distance between the heavier and lighter weights have changed. This is the general principle behind how a crane stays balanced.




After balancing both the load and the counterweight, cranes have to have a very strong base to support everything. They support this enormous weight through retractable legs called outriggers, which work similar to training wheels on a bike. 2 or more of these extend out onto the ground to provide a wider base of support. Lifting a heavy load creates a force that acts downward on a crane’s centre of gravity. This generates a rotational force – also known as torque – which could cause the whole thing to tip over if the stability limit is exceeded. It’s therefore very important to use outriggers to improve stability. They contain pads on the end of each leg, which spread the force further over a larger section of ground. Taking the force off the wheels of the crane and translating it to something more stable, like the ground, is also an important function of these legs. It’s essential that the operator is aware of the maximum force that they can carry to ensure the safety of everyone on the site.




The crane boom is the big arm that extends and retracts to move loads. Mobile cranes commonly have telescopic booms, which are a number of tubes stacked inside each other like a Russian doll when retracted. These extend with hydraulic force, which is where pistons are used to push the smallest piece of the boom out first to enable the crane to reach great lengths. Where the jib is the secondary arm that extends off the boom, the boom is the main moving part. It’s one of the heaviest moving parts of the crane – besides the counterweight – and it’s this that requires the most stability from the things mentioned above.


All in all, cranes are a tremendous mechanical feat. At St George cranes, we provide safe and efficient crane hire. Now that you understand the capabilities of a crane a bit better, make them work for you on your next build by contacting us so we can provide you with a solution to your construction needs.

Date posted: March 2, 2023 | St George Cranes