5.3.1 Section B Flashcards
B1.1 When a vehicle changes direction at speed, is weight enough to stop unsecured cargo from sliding off?
No. Friction or weight is not enough. It is wrong to assume that the weight of the load itself will keep it securely in position.
B1.2 Under heavy braking what is the weight acting in a forward direction equal to?
Under heavy braking, the weight acting in a forward direction can be equal to that acting down on the vehicle.
The forces acting on the load during braking increase with the rate of deceleration and the weigh of the load. So, when the vehicle is braked, the load will want to continue to move in its original direction.
B1.3 What is centrifugal force?
When the vehicle takes a curved path at a bend, the forces acting upon it tend to cause it to continue on the original straight course.
At normal speeds this is overcome by the grip between the tyres and the road surface. If a truck takes a bend too fast, centrifugal force will cause the vehicle and any load to be thrown towards the outside of the bend.
B1.4 What is vehicle momentum?
The force that keeps the vehicle rolling.
B1.5 What does road camber refer to?
The slope of the road from the centre to the edge.
B1.6 Define the centre of gravity of a vehicle?
Is the point around which all the vehicle weight is balanced.
B1.7 What is the tipping edge of a vehicle?
This is the point at which the vehicle will try to overturn as a result of a change to the location of its centre of gravity.
B1.8 What problems do liquid loads produce in comparison to solid loads?
When carrying bulk liquid, driving at speed on bends can cause rollovers. Roundabouts are a typical S-bend that can cause rollovers. If the liquid is on one side during the first curve left onto the roundabout, then shifts to the other side during the next curve, the fluid is positioned to shift back to the first side with four times the centrifugal force it had during the initial curve.
B1.9 What is kinetic energy?
This is the energy that is stored up in the truck when it is travelling along. Efficient use of this energy can be used to reduce fuel consumption, by easing off the accelerator in good time when approaching a bend, roundabout, or other road feature such as traffic lights or a pedestrian crossing. This allows the truck to reduce speed gradually and avoid the need for harsh braking. It can also avoid the need to engage lower gears and harder acceleration in order to resume normal speeds.
Kinetic energy is converted into heat at the brake shoes and drums, and is wasted when braking occurs.
B1.10 What precautions should be taken when transporting hanging loads?
Hanging loads such as carcasses or garments should be properly secured to minimise swinging or sliding inside the vehicle. When movement occurs, the load and centre of gravity moves, and is likely to affect the driving dynamics of the vehicle.
Hanging loads will start to swing longitudinally as a result of the vehicle accelerating and decelerating. When the vehicle changes direction, the hanging load will swing sideways. This could make the vehicle more difficult to control.
