Trucks and Semis have different braking systems compared to normal vehicles. This is a result of the vehicles length and body shape and conversely, the vehicle’s centre of gravity. They then present an interesting dynamic since any loading on the vehicle will most certainly have a bearing on the truck’s turning as well as braking.
This is most noticeable when you take the situation of a truck that loses control when trying to brake on a slippery ice-covered road. What you’ll notice is that when the truck swerves and tries to break, the nose of the truck, as well as the back of the truck, will seemingly swerve around the middle part of the truck. But why does that happen? It’s a result of the combined forces of inertia and centrifugal force.
Inertia can be considered as the force that wants to keep you in a certain state. An example would be when you’re in an elevator. Once the elevator goes up, you feel as if you’re being pulled into the ground, that’s inertia trying to keep you in a state of rest. The same works for when you’re in an elevator heading down, and it stops; you feel as if there is a forcing pull you into the ground as the elevator stops. This is inertia trying to keep you in state of movement. The same applies to the truck when the driver hits the brakes; the force of inertia tries to keep the vehicle in motion. The force experienced is directly proportional to the mass of the object, and since this is a whole truck, then it implies that the force of inertia is quite great. This is one contributing factor to the reason why the truck ends up in its swerved state. However, the apparent rotation of the truck’s back cargo is a result of another force known as centrifugal force.
This force occurs on a body in curvilinear motion drawing a body away from the centre of rotation. An example of this would be when you tie a stone to the end of a strong and spin the rock round and round. It feels as if the stone wants to fly off (and would probably do so if the string were to cut). The same occurs with the truck. The load at the back of the truck is not part of the braking system. As such, when the driver hits the brakes, the back of the truck attempts to remain in motion. In this case, since the brakes are applying a force in the opposite direction, they became a pseudo – centre of gravity. What happens then is that the load swings about this centre of gravity and thus the apparent rotation of the back of the truck. Notice, that just as a heavier rock on the end of your string would generate a heavier centrifugal force, so too would a heavier truckload. Another interesting factor to consider would be the length of the load from the centre of gravity.
Going back to the example of the rock at the end of the string, if you had a longer string, you would be able to generate a greater force. The same applies to the truck, and if you excessively load the back of the truck, you are in danger of having a greater centrifugal force occurring in the case of sudden braking. This is the reason why most truckers are encouraged to load the front sections of their trucks.
A professor at Cambridge University, David Cebon, recently came up with a system that optimised braking and turning mechanisms in trucks through onboard computers. The system basically monitored the vehicle dynamics, the inertia forces experienced on the axles and basically self – corrects the vehicle before any serious swerving occurs. These braking actuators are designed to be energy efficient as well. This implies that truckers will not have to worry about getting more truck spare parts due to heavy stress on braking systems as the system will also redistribute force applied over the different truck components.